#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
-STATISTIC(NumRemoved , "Number of aux indvars removed");
-STATISTIC(NumInserted, "Number of canonical indvars added");
-STATISTIC(NumReplaced, "Number of exit values replaced");
-STATISTIC(NumLFTR , "Number of loop exit tests replaced");
+STATISTIC(NumRemoved , "Number of aux indvars removed");
+STATISTIC(NumWidened , "Number of indvars widened");
+STATISTIC(NumInserted , "Number of canonical indvars added");
+STATISTIC(NumReplaced , "Number of exit values replaced");
+STATISTIC(NumLFTR , "Number of loop exit tests replaced");
+STATISTIC(NumElimIdentity, "Number of IV identities eliminated");
+STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
+STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
+STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
+STATISTIC(NumElimIV , "Number of congruent IVs eliminated");
+
+static cl::opt<bool> DisableIVRewrite(
+ "disable-iv-rewrite", cl::Hidden,
+ cl::desc("Disable canonical induction variable rewriting"));
+
+// Temporary flag for use with -disable-iv-rewrite to force a canonical IV for
+// LFTR purposes.
+static cl::opt<bool> ForceLFTR(
+ "force-lftr", cl::Hidden,
+ cl::desc("Enable forced linear function test replacement"));
namespace {
class IndVarSimplify : public LoopPass {
LoopInfo *LI;
ScalarEvolution *SE;
DominatorTree *DT;
+ TargetData *TD;
+
+ SmallVector<WeakVH, 16> DeadInsts;
bool Changed;
public:
static char ID; // Pass identification, replacement for typeid
- IndVarSimplify() : LoopPass(&ID) {}
+ IndVarSimplify() : LoopPass(ID), IU(0), LI(0), SE(0), DT(0), TD(0),
+ Changed(false) {
+ initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
+ }
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
AU.addRequired<ScalarEvolution>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
- AU.addRequired<IVUsers>();
+ if (!DisableIVRewrite)
+ AU.addRequired<IVUsers>();
AU.addPreserved<ScalarEvolution>();
AU.addPreservedID(LoopSimplifyID);
AU.addPreservedID(LCSSAID);
- AU.addPreserved<IVUsers>();
+ if (!DisableIVRewrite)
+ AU.addPreserved<IVUsers>();
AU.setPreservesCFG();
}
private:
+ virtual void releaseMemory() {
+ DeadInsts.clear();
+ }
+
+ bool isValidRewrite(Value *FromVal, Value *ToVal);
- void EliminateIVComparisons();
+ void HandleFloatingPointIV(Loop *L, PHINode *PH);
void RewriteNonIntegerIVs(Loop *L);
- ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
- Value *IndVar,
- BasicBlock *ExitingBlock,
- BranchInst *BI,
- SCEVExpander &Rewriter);
void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
+ void SimplifyIVUsers(SCEVExpander &Rewriter);
+ void SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter);
+
+ bool EliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
+ void EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
+ void EliminateIVRemainder(BinaryOperator *Rem,
+ Value *IVOperand,
+ bool IsSigned);
+
+ void SimplifyCongruentIVs(Loop *L);
+
void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
- void SinkUnusedInvariants(Loop *L);
+ Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
+ PHINode *IndVar, SCEVExpander &Rewriter);
- void HandleFloatingPointIV(Loop *L, PHINode *PH);
+ void SinkUnusedInvariants(Loop *L);
};
}
char IndVarSimplify::ID = 0;
-static RegisterPass<IndVarSimplify>
-X("indvars", "Canonicalize Induction Variables");
+INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
+ "Induction Variable Simplification", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
+INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(IVUsers)
+INITIALIZE_PASS_END(IndVarSimplify, "indvars",
+ "Induction Variable Simplification", false, false)
Pass *llvm::createIndVarSimplifyPass() {
return new IndVarSimplify();
}
-/// LinearFunctionTestReplace - This method rewrites the exit condition of the
-/// loop to be a canonical != comparison against the incremented loop induction
-/// variable. This pass is able to rewrite the exit tests of any loop where the
-/// SCEV analysis can determine a loop-invariant trip count of the loop, which
-/// is actually a much broader range than just linear tests.
-ICmpInst *IndVarSimplify::LinearFunctionTestReplace(Loop *L,
- const SCEV *BackedgeTakenCount,
- Value *IndVar,
- BasicBlock *ExitingBlock,
- BranchInst *BI,
- SCEVExpander &Rewriter) {
- // If the exiting block is not the same as the backedge block, we must compare
- // against the preincremented value, otherwise we prefer to compare against
- // the post-incremented value.
- Value *CmpIndVar;
- const SCEV *RHS = BackedgeTakenCount;
- if (ExitingBlock == L->getLoopLatch()) {
- // Add one to the "backedge-taken" count to get the trip count.
- // If this addition may overflow, we have to be more pessimistic and
- // cast the induction variable before doing the add.
- const SCEV *Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
- const SCEV *N =
- SE->getAddExpr(BackedgeTakenCount,
- SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
- if ((isa<SCEVConstant>(N) && !N->isZero()) ||
- SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
- // No overflow. Cast the sum.
- RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
- } else {
- // Potential overflow. Cast before doing the add.
- RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
- IndVar->getType());
- RHS = SE->getAddExpr(RHS,
- SE->getIntegerSCEV(1, IndVar->getType()));
- }
-
- // The BackedgeTaken expression contains the number of times that the
- // backedge branches to the loop header. This is one less than the
- // number of times the loop executes, so use the incremented indvar.
- CmpIndVar = L->getCanonicalInductionVariableIncrement();
- } else {
- // We have to use the preincremented value...
- RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
- IndVar->getType());
- CmpIndVar = IndVar;
+/// isValidRewrite - Return true if the SCEV expansion generated by the
+/// rewriter can replace the original value. SCEV guarantees that it
+/// produces the same value, but the way it is produced may be illegal IR.
+/// Ideally, this function will only be called for verification.
+bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) {
+ // If an SCEV expression subsumed multiple pointers, its expansion could
+ // reassociate the GEP changing the base pointer. This is illegal because the
+ // final address produced by a GEP chain must be inbounds relative to its
+ // underlying object. Otherwise basic alias analysis, among other things,
+ // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid
+ // producing an expression involving multiple pointers. Until then, we must
+ // bail out here.
+ //
+ // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject
+ // because it understands lcssa phis while SCEV does not.
+ Value *FromPtr = FromVal;
+ Value *ToPtr = ToVal;
+ if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) {
+ FromPtr = GEP->getPointerOperand();
}
+ if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) {
+ ToPtr = GEP->getPointerOperand();
+ }
+ if (FromPtr != FromVal || ToPtr != ToVal) {
+ // Quickly check the common case
+ if (FromPtr == ToPtr)
+ return true;
+
+ // SCEV may have rewritten an expression that produces the GEP's pointer
+ // operand. That's ok as long as the pointer operand has the same base
+ // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the
+ // base of a recurrence. This handles the case in which SCEV expansion
+ // converts a pointer type recurrence into a nonrecurrent pointer base
+ // indexed by an integer recurrence.
+ const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
+ const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
+ if (FromBase == ToBase)
+ return true;
+
+ DEBUG(dbgs() << "INDVARS: GEP rewrite bail out "
+ << *FromBase << " != " << *ToBase << "\n");
- // Expand the code for the iteration count.
- assert(RHS->isLoopInvariant(L) &&
- "Computed iteration count is not loop invariant!");
- Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI);
-
- // Insert a new icmp_ne or icmp_eq instruction before the branch.
- ICmpInst::Predicate Opcode;
- if (L->contains(BI->getSuccessor(0)))
- Opcode = ICmpInst::ICMP_NE;
- else
- Opcode = ICmpInst::ICMP_EQ;
+ return false;
+ }
+ return true;
+}
- DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
- << " LHS:" << *CmpIndVar << '\n'
- << " op:\t"
- << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
- << " RHS:\t" << *RHS << "\n");
+/// Determine the insertion point for this user. By default, insert immediately
+/// before the user. SCEVExpander or LICM will hoist loop invariants out of the
+/// loop. For PHI nodes, there may be multiple uses, so compute the nearest
+/// common dominator for the incoming blocks.
+static Instruction *getInsertPointForUses(Instruction *User, Value *Def,
+ DominatorTree *DT) {
+ PHINode *PHI = dyn_cast<PHINode>(User);
+ if (!PHI)
+ return User;
+
+ Instruction *InsertPt = 0;
+ for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
+ if (PHI->getIncomingValue(i) != Def)
+ continue;
- ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
+ BasicBlock *InsertBB = PHI->getIncomingBlock(i);
+ if (!InsertPt) {
+ InsertPt = InsertBB->getTerminator();
+ continue;
+ }
+ InsertBB = DT->findNearestCommonDominator(InsertPt->getParent(), InsertBB);
+ InsertPt = InsertBB->getTerminator();
+ }
+ assert(InsertPt && "Missing phi operand");
+ assert((!isa<Instruction>(Def) ||
+ DT->dominates(cast<Instruction>(Def), InsertPt)) &&
+ "def does not dominate all uses");
+ return InsertPt;
+}
- Value *OrigCond = BI->getCondition();
- // It's tempting to use replaceAllUsesWith here to fully replace the old
- // comparison, but that's not immediately safe, since users of the old
- // comparison may not be dominated by the new comparison. Instead, just
- // update the branch to use the new comparison; in the common case this
- // will make old comparison dead.
- BI->setCondition(Cond);
- RecursivelyDeleteTriviallyDeadInstructions(OrigCond);
+//===----------------------------------------------------------------------===//
+// RewriteNonIntegerIVs and helpers. Prefer integer IVs.
+//===----------------------------------------------------------------------===//
- ++NumLFTR;
- Changed = true;
- return Cond;
+/// ConvertToSInt - Convert APF to an integer, if possible.
+static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
+ bool isExact = false;
+ if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
+ return false;
+ // See if we can convert this to an int64_t
+ uint64_t UIntVal;
+ if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
+ &isExact) != APFloat::opOK || !isExact)
+ return false;
+ IntVal = UIntVal;
+ return true;
}
-/// RewriteLoopExitValues - Check to see if this loop has a computable
-/// loop-invariant execution count. If so, this means that we can compute the
-/// final value of any expressions that are recurrent in the loop, and
-/// substitute the exit values from the loop into any instructions outside of
-/// the loop that use the final values of the current expressions.
+/// HandleFloatingPointIV - If the loop has floating induction variable
+/// then insert corresponding integer induction variable if possible.
+/// For example,
+/// for(double i = 0; i < 10000; ++i)
+/// bar(i)
+/// is converted into
+/// for(int i = 0; i < 10000; ++i)
+/// bar((double)i);
///
-/// This is mostly redundant with the regular IndVarSimplify activities that
-/// happen later, except that it's more powerful in some cases, because it's
-/// able to brute-force evaluate arbitrary instructions as long as they have
-/// constant operands at the beginning of the loop.
-void IndVarSimplify::RewriteLoopExitValues(Loop *L,
- SCEVExpander &Rewriter) {
- // Verify the input to the pass in already in LCSSA form.
- assert(L->isLCSSAForm(*DT));
+void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
+ unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
+ unsigned BackEdge = IncomingEdge^1;
- SmallVector<BasicBlock*, 8> ExitBlocks;
- L->getUniqueExitBlocks(ExitBlocks);
+ // Check incoming value.
+ ConstantFP *InitValueVal =
+ dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
- // Find all values that are computed inside the loop, but used outside of it.
- // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
- // the exit blocks of the loop to find them.
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
- BasicBlock *ExitBB = ExitBlocks[i];
+ int64_t InitValue;
+ if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
+ return;
- // If there are no PHI nodes in this exit block, then no values defined
- // inside the loop are used on this path, skip it.
- PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
- if (!PN) continue;
+ // Check IV increment. Reject this PN if increment operation is not
+ // an add or increment value can not be represented by an integer.
+ BinaryOperator *Incr =
+ dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
+ if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
- unsigned NumPreds = PN->getNumIncomingValues();
+ // If this is not an add of the PHI with a constantfp, or if the constant fp
+ // is not an integer, bail out.
+ ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
+ int64_t IncValue;
+ if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
+ !ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
+ return;
- // Iterate over all of the PHI nodes.
- BasicBlock::iterator BBI = ExitBB->begin();
- while ((PN = dyn_cast<PHINode>(BBI++))) {
- if (PN->use_empty())
- continue; // dead use, don't replace it
+ // Check Incr uses. One user is PN and the other user is an exit condition
+ // used by the conditional terminator.
+ Value::use_iterator IncrUse = Incr->use_begin();
+ Instruction *U1 = cast<Instruction>(*IncrUse++);
+ if (IncrUse == Incr->use_end()) return;
+ Instruction *U2 = cast<Instruction>(*IncrUse++);
+ if (IncrUse != Incr->use_end()) return;
- // SCEV only supports integer expressions for now.
- if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
- continue;
+ // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
+ // only used by a branch, we can't transform it.
+ FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
+ if (!Compare)
+ Compare = dyn_cast<FCmpInst>(U2);
+ if (Compare == 0 || !Compare->hasOneUse() ||
+ !isa<BranchInst>(Compare->use_back()))
+ return;
- // It's necessary to tell ScalarEvolution about this explicitly so that
- // it can walk the def-use list and forget all SCEVs, as it may not be
- // watching the PHI itself. Once the new exit value is in place, there
- // may not be a def-use connection between the loop and every instruction
- // which got a SCEVAddRecExpr for that loop.
- SE->forgetValue(PN);
+ BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
- // Iterate over all of the values in all the PHI nodes.
- for (unsigned i = 0; i != NumPreds; ++i) {
- // If the value being merged in is not integer or is not defined
- // in the loop, skip it.
- Value *InVal = PN->getIncomingValue(i);
- if (!isa<Instruction>(InVal))
- continue;
+ // We need to verify that the branch actually controls the iteration count
+ // of the loop. If not, the new IV can overflow and no one will notice.
+ // The branch block must be in the loop and one of the successors must be out
+ // of the loop.
+ assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
+ if (!L->contains(TheBr->getParent()) ||
+ (L->contains(TheBr->getSuccessor(0)) &&
+ L->contains(TheBr->getSuccessor(1))))
+ return;
- // If this pred is for a subloop, not L itself, skip it.
- if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
- continue; // The Block is in a subloop, skip it.
- // Check that InVal is defined in the loop.
- Instruction *Inst = cast<Instruction>(InVal);
- if (!L->contains(Inst))
- continue;
+ // If it isn't a comparison with an integer-as-fp (the exit value), we can't
+ // transform it.
+ ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
+ int64_t ExitValue;
+ if (ExitValueVal == 0 ||
+ !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
+ return;
- // Okay, this instruction has a user outside of the current loop
- // and varies predictably *inside* the loop. Evaluate the value it
- // contains when the loop exits, if possible.
- const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
- if (!ExitValue->isLoopInvariant(L))
- continue;
+ // Find new predicate for integer comparison.
+ CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
+ switch (Compare->getPredicate()) {
+ default: return; // Unknown comparison.
+ case CmpInst::FCMP_OEQ:
+ case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
+ case CmpInst::FCMP_ONE:
+ case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
+ case CmpInst::FCMP_OGT:
+ case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
+ case CmpInst::FCMP_OGE:
+ case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
+ case CmpInst::FCMP_OLT:
+ case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
+ case CmpInst::FCMP_OLE:
+ case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
+ }
- Changed = true;
- ++NumReplaced;
+ // We convert the floating point induction variable to a signed i32 value if
+ // we can. This is only safe if the comparison will not overflow in a way
+ // that won't be trapped by the integer equivalent operations. Check for this
+ // now.
+ // TODO: We could use i64 if it is native and the range requires it.
- Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
+ // The start/stride/exit values must all fit in signed i32.
+ if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
+ return;
- DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
- << " LoopVal = " << *Inst << "\n");
+ // If not actually striding (add x, 0.0), avoid touching the code.
+ if (IncValue == 0)
+ return;
- PN->setIncomingValue(i, ExitVal);
+ // Positive and negative strides have different safety conditions.
+ if (IncValue > 0) {
+ // If we have a positive stride, we require the init to be less than the
+ // exit value and an equality or less than comparison.
+ if (InitValue >= ExitValue ||
+ NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
+ return;
- // If this instruction is dead now, delete it.
- RecursivelyDeleteTriviallyDeadInstructions(Inst);
+ uint32_t Range = uint32_t(ExitValue-InitValue);
+ if (NewPred == CmpInst::ICMP_SLE) {
+ // Normalize SLE -> SLT, check for infinite loop.
+ if (++Range == 0) return; // Range overflows.
+ }
- if (NumPreds == 1) {
- // Completely replace a single-pred PHI. This is safe, because the
- // NewVal won't be variant in the loop, so we don't need an LCSSA phi
- // node anymore.
- PN->replaceAllUsesWith(ExitVal);
- RecursivelyDeleteTriviallyDeadInstructions(PN);
- }
- }
- if (NumPreds != 1) {
- // Clone the PHI and delete the original one. This lets IVUsers and
- // any other maps purge the original user from their records.
- PHINode *NewPN = cast<PHINode>(PN->clone());
- NewPN->takeName(PN);
- NewPN->insertBefore(PN);
- PN->replaceAllUsesWith(NewPN);
- PN->eraseFromParent();
- }
+ unsigned Leftover = Range % uint32_t(IncValue);
+
+ // If this is an equality comparison, we require that the strided value
+ // exactly land on the exit value, otherwise the IV condition will wrap
+ // around and do things the fp IV wouldn't.
+ if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
+ Leftover != 0)
+ return;
+
+ // If the stride would wrap around the i32 before exiting, we can't
+ // transform the IV.
+ if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
+ return;
+
+ } else {
+ // If we have a negative stride, we require the init to be greater than the
+ // exit value and an equality or greater than comparison.
+ if (InitValue >= ExitValue ||
+ NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
+ return;
+
+ uint32_t Range = uint32_t(InitValue-ExitValue);
+ if (NewPred == CmpInst::ICMP_SGE) {
+ // Normalize SGE -> SGT, check for infinite loop.
+ if (++Range == 0) return; // Range overflows.
}
+
+ unsigned Leftover = Range % uint32_t(-IncValue);
+
+ // If this is an equality comparison, we require that the strided value
+ // exactly land on the exit value, otherwise the IV condition will wrap
+ // around and do things the fp IV wouldn't.
+ if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
+ Leftover != 0)
+ return;
+
+ // If the stride would wrap around the i32 before exiting, we can't
+ // transform the IV.
+ if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
+ return;
}
- // The insertion point instruction may have been deleted; clear it out
- // so that the rewriter doesn't trip over it later.
- Rewriter.clearInsertPoint();
+ IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
+
+ // Insert new integer induction variable.
+ PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
+ NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
+ PN->getIncomingBlock(IncomingEdge));
+
+ Value *NewAdd =
+ BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
+ Incr->getName()+".int", Incr);
+ NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
+
+ ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
+ ConstantInt::get(Int32Ty, ExitValue),
+ Compare->getName());
+
+ // In the following deletions, PN may become dead and may be deleted.
+ // Use a WeakVH to observe whether this happens.
+ WeakVH WeakPH = PN;
+
+ // Delete the old floating point exit comparison. The branch starts using the
+ // new comparison.
+ NewCompare->takeName(Compare);
+ Compare->replaceAllUsesWith(NewCompare);
+ RecursivelyDeleteTriviallyDeadInstructions(Compare);
+
+ // Delete the old floating point increment.
+ Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
+ RecursivelyDeleteTriviallyDeadInstructions(Incr);
+
+ // If the FP induction variable still has uses, this is because something else
+ // in the loop uses its value. In order to canonicalize the induction
+ // variable, we chose to eliminate the IV and rewrite it in terms of an
+ // int->fp cast.
+ //
+ // We give preference to sitofp over uitofp because it is faster on most
+ // platforms.
+ if (WeakPH) {
+ Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
+ PN->getParent()->getFirstNonPHI());
+ PN->replaceAllUsesWith(Conv);
+ RecursivelyDeleteTriviallyDeadInstructions(PN);
+ }
+
+ // Add a new IVUsers entry for the newly-created integer PHI.
+ if (IU)
+ IU->AddUsersIfInteresting(NewPHI);
}
void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
// If there are, change them into integer recurrences, permitting analysis by
// the SCEV routines.
//
- BasicBlock *Header = L->getHeader();
+ BasicBlock *Header = L->getHeader();
SmallVector<WeakVH, 8> PHIs;
for (BasicBlock::iterator I = Header->begin();
PHIs.push_back(PN);
for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
- if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i]))
+ if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i]))
HandleFloatingPointIV(L, PN);
// If the loop previously had floating-point IV, ScalarEvolution
SE->forgetLoop(L);
}
-void IndVarSimplify::EliminateIVComparisons() {
- SmallVector<WeakVH, 16> DeadInsts;
+//===----------------------------------------------------------------------===//
+// RewriteLoopExitValues - Optimize IV users outside the loop.
+// As a side effect, reduces the amount of IV processing within the loop.
+//===----------------------------------------------------------------------===//
- // Look for ICmp users.
- for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
- IVStrideUse &UI = *I;
- ICmpInst *ICmp = dyn_cast<ICmpInst>(UI.getUser());
- if (!ICmp) continue;
+/// RewriteLoopExitValues - Check to see if this loop has a computable
+/// loop-invariant execution count. If so, this means that we can compute the
+/// final value of any expressions that are recurrent in the loop, and
+/// substitute the exit values from the loop into any instructions outside of
+/// the loop that use the final values of the current expressions.
+///
+/// This is mostly redundant with the regular IndVarSimplify activities that
+/// happen later, except that it's more powerful in some cases, because it's
+/// able to brute-force evaluate arbitrary instructions as long as they have
+/// constant operands at the beginning of the loop.
+void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
+ // Verify the input to the pass in already in LCSSA form.
+ assert(L->isLCSSAForm(*DT));
- bool Swapped = UI.getOperandValToReplace() == ICmp->getOperand(1);
- ICmpInst::Predicate Pred = ICmp->getPredicate();
- if (Swapped) Pred = ICmpInst::getSwappedPredicate(Pred);
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ L->getUniqueExitBlocks(ExitBlocks);
- // Get the SCEVs for the ICmp operands.
- const SCEV *S = IU->getReplacementExpr(UI);
- const SCEV *X = SE->getSCEV(ICmp->getOperand(!Swapped));
+ // Find all values that are computed inside the loop, but used outside of it.
+ // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan
+ // the exit blocks of the loop to find them.
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+ BasicBlock *ExitBB = ExitBlocks[i];
- // Simplify unnecessary loops away.
- const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
- S = SE->getSCEVAtScope(S, ICmpLoop);
- X = SE->getSCEVAtScope(X, ICmpLoop);
+ // If there are no PHI nodes in this exit block, then no values defined
+ // inside the loop are used on this path, skip it.
+ PHINode *PN = dyn_cast<PHINode>(ExitBB->begin());
+ if (!PN) continue;
- // If the condition is always true or always false, replace it with
- // a constant value.
- if (SE->isKnownPredicate(Pred, S, X))
- ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
- else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
- ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
- else
- continue;
+ unsigned NumPreds = PN->getNumIncomingValues();
- DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
- DeadInsts.push_back(ICmp);
- }
+ // Iterate over all of the PHI nodes.
+ BasicBlock::iterator BBI = ExitBB->begin();
+ while ((PN = dyn_cast<PHINode>(BBI++))) {
+ if (PN->use_empty())
+ continue; // dead use, don't replace it
- // Now that we're done iterating through lists, clean up any instructions
- // which are now dead.
- while (!DeadInsts.empty())
- if (Instruction *Inst =
- dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
- RecursivelyDeleteTriviallyDeadInstructions(Inst);
-}
+ // SCEV only supports integer expressions for now.
+ if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
+ continue;
-bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
- IU = &getAnalysis<IVUsers>();
- LI = &getAnalysis<LoopInfo>();
- SE = &getAnalysis<ScalarEvolution>();
- DT = &getAnalysis<DominatorTree>();
- Changed = false;
+ // It's necessary to tell ScalarEvolution about this explicitly so that
+ // it can walk the def-use list and forget all SCEVs, as it may not be
+ // watching the PHI itself. Once the new exit value is in place, there
+ // may not be a def-use connection between the loop and every instruction
+ // which got a SCEVAddRecExpr for that loop.
+ SE->forgetValue(PN);
- // If there are any floating-point recurrences, attempt to
- // transform them to use integer recurrences.
- RewriteNonIntegerIVs(L);
+ // Iterate over all of the values in all the PHI nodes.
+ for (unsigned i = 0; i != NumPreds; ++i) {
+ // If the value being merged in is not integer or is not defined
+ // in the loop, skip it.
+ Value *InVal = PN->getIncomingValue(i);
+ if (!isa<Instruction>(InVal))
+ continue;
- BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
- const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
+ // If this pred is for a subloop, not L itself, skip it.
+ if (LI->getLoopFor(PN->getIncomingBlock(i)) != L)
+ continue; // The Block is in a subloop, skip it.
- // Create a rewriter object which we'll use to transform the code with.
- SCEVExpander Rewriter(*SE);
+ // Check that InVal is defined in the loop.
+ Instruction *Inst = cast<Instruction>(InVal);
+ if (!L->contains(Inst))
+ continue;
- // Check to see if this loop has a computable loop-invariant execution count.
- // If so, this means that we can compute the final value of any expressions
- // that are recurrent in the loop, and substitute the exit values from the
- // loop into any instructions outside of the loop that use the final values of
- // the current expressions.
- //
- if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
- RewriteLoopExitValues(L, Rewriter);
+ // Okay, this instruction has a user outside of the current loop
+ // and varies predictably *inside* the loop. Evaluate the value it
+ // contains when the loop exits, if possible.
+ const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
+ if (!SE->isLoopInvariant(ExitValue, L))
+ continue;
- // Compute the type of the largest recurrence expression, and decide whether
- // a canonical induction variable should be inserted.
- const Type *LargestType = 0;
- bool NeedCannIV = false;
- if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
- LargestType = BackedgeTakenCount->getType();
- LargestType = SE->getEffectiveSCEVType(LargestType);
- // If we have a known trip count and a single exit block, we'll be
- // rewriting the loop exit test condition below, which requires a
- // canonical induction variable.
- if (ExitingBlock)
- NeedCannIV = true;
- }
- for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
- const Type *Ty =
- SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
- if (!LargestType ||
- SE->getTypeSizeInBits(Ty) >
- SE->getTypeSizeInBits(LargestType))
- LargestType = Ty;
- NeedCannIV = true;
- }
+ Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
- // Now that we know the largest of the induction variable expressions
- // in this loop, insert a canonical induction variable of the largest size.
- Value *IndVar = 0;
- if (NeedCannIV) {
- // Check to see if the loop already has any canonical-looking induction
- // variables. If any are present and wider than the planned canonical
- // induction variable, temporarily remove them, so that the Rewriter
- // doesn't attempt to reuse them.
- SmallVector<PHINode *, 2> OldCannIVs;
- while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
- if (SE->getTypeSizeInBits(OldCannIV->getType()) >
- SE->getTypeSizeInBits(LargestType))
- OldCannIV->removeFromParent();
- else
- break;
- OldCannIVs.push_back(OldCannIV);
- }
+ DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
+ << " LoopVal = " << *Inst << "\n");
- IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);
+ if (!isValidRewrite(Inst, ExitVal)) {
+ DeadInsts.push_back(ExitVal);
+ continue;
+ }
+ Changed = true;
+ ++NumReplaced;
- ++NumInserted;
- Changed = true;
- DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');
+ PN->setIncomingValue(i, ExitVal);
- // Now that the official induction variable is established, reinsert
- // any old canonical-looking variables after it so that the IR remains
- // consistent. They will be deleted as part of the dead-PHI deletion at
- // the end of the pass.
- while (!OldCannIVs.empty()) {
- PHINode *OldCannIV = OldCannIVs.pop_back_val();
- OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
- }
- }
+ // If this instruction is dead now, delete it.
+ RecursivelyDeleteTriviallyDeadInstructions(Inst);
- // If we have a trip count expression, rewrite the loop's exit condition
- // using it. We can currently only handle loops with a single exit.
- ICmpInst *NewICmp = 0;
- if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
- !BackedgeTakenCount->isZero() &&
- ExitingBlock) {
- assert(NeedCannIV &&
- "LinearFunctionTestReplace requires a canonical induction variable");
-
- // Can't rewrite non-branch yet.
- if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
- // Eliminate comparisons which are always true or always false, due to
- // the known backedge-taken count. This may include comparisons which
- // are currently controlling (part of) the loop exit, so we can only do
- // it when we know we're going to insert our own loop exit code.
- EliminateIVComparisons();
-
- // Insert new loop exit code.
- NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
- ExitingBlock, BI, Rewriter);
+ if (NumPreds == 1) {
+ // Completely replace a single-pred PHI. This is safe, because the
+ // NewVal won't be variant in the loop, so we don't need an LCSSA phi
+ // node anymore.
+ PN->replaceAllUsesWith(ExitVal);
+ RecursivelyDeleteTriviallyDeadInstructions(PN);
+ }
+ }
+ if (NumPreds != 1) {
+ // Clone the PHI and delete the original one. This lets IVUsers and
+ // any other maps purge the original user from their records.
+ PHINode *NewPN = cast<PHINode>(PN->clone());
+ NewPN->takeName(PN);
+ NewPN->insertBefore(PN);
+ PN->replaceAllUsesWith(NewPN);
+ PN->eraseFromParent();
+ }
}
}
- // Rewrite IV-derived expressions. Clears the rewriter cache.
- RewriteIVExpressions(L, Rewriter);
-
- // The Rewriter may not be used from this point on.
+ // The insertion point instruction may have been deleted; clear it out
+ // so that the rewriter doesn't trip over it later.
+ Rewriter.clearInsertPoint();
+}
- // Loop-invariant instructions in the preheader that aren't used in the
- // loop may be sunk below the loop to reduce register pressure.
- SinkUnusedInvariants(L);
+//===----------------------------------------------------------------------===//
+// Rewrite IV users based on a canonical IV.
+// To be replaced by -disable-iv-rewrite.
+//===----------------------------------------------------------------------===//
- // For completeness, inform IVUsers of the IV use in the newly-created
- // loop exit test instruction.
- if (NewICmp)
- IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
-
- // Clean up dead instructions.
- Changed |= DeleteDeadPHIs(L->getHeader());
- // Check a post-condition.
- assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
- return Changed;
+/// SimplifyIVUsers - Iteratively perform simplification on IVUsers within this
+/// loop. IVUsers is treated as a worklist. Each successive simplification may
+/// push more users which may themselves be candidates for simplification.
+///
+/// This is the old approach to IV simplification to be replaced by
+/// SimplifyIVUsersNoRewrite.
+///
+void IndVarSimplify::SimplifyIVUsers(SCEVExpander &Rewriter) {
+ // Each round of simplification involves a round of eliminating operations
+ // followed by a round of widening IVs. A single IVUsers worklist is used
+ // across all rounds. The inner loop advances the user. If widening exposes
+ // more uses, then another pass through the outer loop is triggered.
+ for (IVUsers::iterator I = IU->begin(); I != IU->end(); ++I) {
+ Instruction *UseInst = I->getUser();
+ Value *IVOperand = I->getOperandValToReplace();
+
+ if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
+ EliminateIVComparison(ICmp, IVOperand);
+ continue;
+ }
+ if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
+ bool IsSigned = Rem->getOpcode() == Instruction::SRem;
+ if (IsSigned || Rem->getOpcode() == Instruction::URem) {
+ EliminateIVRemainder(Rem, IVOperand, IsSigned);
+ continue;
+ }
+ }
+ }
}
// FIXME: It is an extremely bad idea to indvar substitute anything more
// currently can only reduce affine polynomials. For now just disable
// indvar subst on anything more complex than an affine addrec, unless
// it can be expanded to a trivial value.
-static bool isSafe(const SCEV *S, const Loop *L) {
+static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) {
// Loop-invariant values are safe.
- if (S->isLoopInvariant(L)) return true;
+ if (SE->isLoopInvariant(S, L)) return true;
// Affine addrecs are safe. Non-affine are not, because LSR doesn't know how
// to transform them into efficient code.
if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) {
for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(),
E = Commutative->op_end(); I != E; ++I)
- if (!isSafe(*I, L)) return false;
+ if (!isSafe(*I, L, SE)) return false;
return true;
}
-
+
// A cast is safe if its operand is.
if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
- return isSafe(C->getOperand(), L);
+ return isSafe(C->getOperand(), L, SE);
// A udiv is safe if its operands are.
if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S))
- return isSafe(UD->getLHS(), L) &&
- isSafe(UD->getRHS(), L);
+ return isSafe(UD->getLHS(), L, SE) &&
+ isSafe(UD->getRHS(), L, SE);
// SCEVUnknown is always safe.
if (isa<SCEVUnknown>(S))
}
void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
- SmallVector<WeakVH, 16> DeadInsts;
-
// Rewrite all induction variable expressions in terms of the canonical
// induction variable.
//
// of different sizes.
for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) {
Value *Op = UI->getOperandValToReplace();
- const Type *UseTy = Op->getType();
+ Type *UseTy = Op->getType();
Instruction *User = UI->getUser();
// Compute the final addrec to expand into code.
// Evaluate the expression out of the loop, if possible.
if (!L->contains(UI->getUser())) {
const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop());
- if (ExitVal->isLoopInvariant(L))
+ if (SE->isLoopInvariant(ExitVal, L))
AR = ExitVal;
}
// currently can only reduce affine polynomials. For now just disable
// indvar subst on anything more complex than an affine addrec, unless
// it can be expanded to a trivial value.
- if (!isSafe(AR, L))
+ if (!isSafe(AR, L, SE))
continue;
// Determine the insertion point for this user. By default, insert
// hoist loop invariants out of the loop. For PHI nodes, there may be
// multiple uses, so compute the nearest common dominator for the
// incoming blocks.
- Instruction *InsertPt = User;
- if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
- for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
- if (PHI->getIncomingValue(i) == Op) {
- if (InsertPt == User)
- InsertPt = PHI->getIncomingBlock(i)->getTerminator();
- else
- InsertPt =
- DT->findNearestCommonDominator(InsertPt->getParent(),
- PHI->getIncomingBlock(i))
- ->getTerminator();
- }
+ Instruction *InsertPt = getInsertPointForUses(User, Op, DT);
// Now expand it into actual Instructions and patch it into place.
Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
+ DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
+ << " into = " << *NewVal << "\n");
+
+ if (!isValidRewrite(Op, NewVal)) {
+ DeadInsts.push_back(NewVal);
+ continue;
+ }
// Inform ScalarEvolution that this value is changing. The change doesn't
// affect its value, but it does potentially affect which use lists the
// value will be on after the replacement, which affects ScalarEvolution's
// Patch the new value into place.
if (Op->hasName())
NewVal->takeName(Op);
+ if (Instruction *NewValI = dyn_cast<Instruction>(NewVal))
+ NewValI->setDebugLoc(User->getDebugLoc());
User->replaceUsesOfWith(Op, NewVal);
UI->setOperandValToReplace(NewVal);
- DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
- << " into = " << *NewVal << "\n");
+
++NumRemoved;
Changed = true;
// The old value may be dead now.
DeadInsts.push_back(Op);
}
+}
- // Clear the rewriter cache, because values that are in the rewriter's cache
- // can be deleted in the loop below, causing the AssertingVH in the cache to
- // trigger.
- Rewriter.clear();
- // Now that we're done iterating through lists, clean up any instructions
- // which are now dead.
- while (!DeadInsts.empty())
- if (Instruction *Inst =
- dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
- RecursivelyDeleteTriviallyDeadInstructions(Inst);
+//===----------------------------------------------------------------------===//
+// IV Widening - Extend the width of an IV to cover its widest uses.
+//===----------------------------------------------------------------------===//
+
+namespace {
+ // Collect information about induction variables that are used by sign/zero
+ // extend operations. This information is recorded by CollectExtend and
+ // provides the input to WidenIV.
+ struct WideIVInfo {
+ Type *WidestNativeType; // Widest integer type created [sz]ext
+ bool IsSigned; // Was an sext user seen before a zext?
+
+ WideIVInfo() : WidestNativeType(0), IsSigned(false) {}
+ };
}
-/// If there's a single exit block, sink any loop-invariant values that
-/// were defined in the preheader but not used inside the loop into the
-/// exit block to reduce register pressure in the loop.
-void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
- BasicBlock *ExitBlock = L->getExitBlock();
- if (!ExitBlock) return;
+/// CollectExtend - Update information about the induction variable that is
+/// extended by this sign or zero extend operation. This is used to determine
+/// the final width of the IV before actually widening it.
+static void CollectExtend(CastInst *Cast, bool IsSigned, WideIVInfo &WI,
+ ScalarEvolution *SE, const TargetData *TD) {
+ Type *Ty = Cast->getType();
+ uint64_t Width = SE->getTypeSizeInBits(Ty);
+ if (TD && !TD->isLegalInteger(Width))
+ return;
- BasicBlock *Preheader = L->getLoopPreheader();
- if (!Preheader) return;
+ if (!WI.WidestNativeType) {
+ WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
+ WI.IsSigned = IsSigned;
+ return;
+ }
- Instruction *InsertPt = ExitBlock->getFirstNonPHI();
- BasicBlock::iterator I = Preheader->getTerminator();
- while (I != Preheader->begin()) {
- --I;
- // New instructions were inserted at the end of the preheader.
- if (isa<PHINode>(I))
- break;
+ // We extend the IV to satisfy the sign of its first user, arbitrarily.
+ if (WI.IsSigned != IsSigned)
+ return;
- // Don't move instructions which might have side effects, since the side
- // effects need to complete before instructions inside the loop. Also don't
- // move instructions which might read memory, since the loop may modify
- // memory. Note that it's okay if the instruction might have undefined
- // behavior: LoopSimplify guarantees that the preheader dominates the exit
- // block.
- if (I->mayHaveSideEffects() || I->mayReadFromMemory())
- continue;
+ if (Width > SE->getTypeSizeInBits(WI.WidestNativeType))
+ WI.WidestNativeType = SE->getEffectiveSCEVType(Ty);
+}
- // Skip debug info intrinsics.
- if (isa<DbgInfoIntrinsic>(I))
- continue;
+namespace {
- // Don't sink static AllocaInsts out of the entry block, which would
- // turn them into dynamic allocas!
- if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
- if (AI->isStaticAlloca())
- continue;
+/// NarrowIVDefUse - Record a link in the Narrow IV def-use chain along with the
+/// WideIV that computes the same value as the Narrow IV def. This avoids
+/// caching Use* pointers.
+struct NarrowIVDefUse {
+ Instruction *NarrowDef;
+ Instruction *NarrowUse;
+ Instruction *WideDef;
- // Determine if there is a use in or before the loop (direct or
- // otherwise).
- bool UsedInLoop = false;
- for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
- UI != UE; ++UI) {
- BasicBlock *UseBB = cast<Instruction>(UI)->getParent();
- if (PHINode *P = dyn_cast<PHINode>(UI)) {
- unsigned i =
- PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
- UseBB = P->getIncomingBlock(i);
- }
- if (UseBB == Preheader || L->contains(UseBB)) {
- UsedInLoop = true;
- break;
- }
- }
+ NarrowIVDefUse(): NarrowDef(0), NarrowUse(0), WideDef(0) {}
- // If there is, the def must remain in the preheader.
- if (UsedInLoop)
- continue;
+ NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD):
+ NarrowDef(ND), NarrowUse(NU), WideDef(WD) {}
+};
- // Otherwise, sink it to the exit block.
- Instruction *ToMove = I;
- bool Done = false;
+/// WidenIV - The goal of this transform is to remove sign and zero extends
+/// without creating any new induction variables. To do this, it creates a new
+/// phi of the wider type and redirects all users, either removing extends or
+/// inserting truncs whenever we stop propagating the type.
+///
+class WidenIV {
+ // Parameters
+ PHINode *OrigPhi;
+ Type *WideType;
+ bool IsSigned;
+
+ // Context
+ LoopInfo *LI;
+ Loop *L;
+ ScalarEvolution *SE;
+ DominatorTree *DT;
+
+ // Result
+ PHINode *WidePhi;
+ Instruction *WideInc;
+ const SCEV *WideIncExpr;
+ SmallVectorImpl<WeakVH> &DeadInsts;
+
+ SmallPtrSet<Instruction*,16> Widened;
+ SmallVector<NarrowIVDefUse, 8> NarrowIVUsers;
+
+public:
+ WidenIV(PHINode *PN, const WideIVInfo &WI, LoopInfo *LInfo,
+ ScalarEvolution *SEv, DominatorTree *DTree,
+ SmallVectorImpl<WeakVH> &DI) :
+ OrigPhi(PN),
+ WideType(WI.WidestNativeType),
+ IsSigned(WI.IsSigned),
+ LI(LInfo),
+ L(LI->getLoopFor(OrigPhi->getParent())),
+ SE(SEv),
+ DT(DTree),
+ WidePhi(0),
+ WideInc(0),
+ WideIncExpr(0),
+ DeadInsts(DI) {
+ assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
+ }
- if (I != Preheader->begin()) {
- // Skip debug info intrinsics.
- do {
- --I;
- } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
+ PHINode *CreateWideIV(SCEVExpander &Rewriter);
- if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
- Done = true;
- } else {
- Done = true;
- }
+protected:
+ Instruction *CloneIVUser(NarrowIVDefUse DU);
- ToMove->moveBefore(InsertPt);
- if (Done) break;
- InsertPt = ToMove;
+ const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse);
+
+ Instruction *WidenIVUse(NarrowIVDefUse DU);
+
+ void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
+};
+} // anonymous namespace
+
+static Value *getExtend( Value *NarrowOper, Type *WideType,
+ bool IsSigned, IRBuilder<> &Builder) {
+ return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) :
+ Builder.CreateZExt(NarrowOper, WideType);
+}
+
+/// CloneIVUser - Instantiate a wide operation to replace a narrow
+/// operation. This only needs to handle operations that can evaluation to
+/// SCEVAddRec. It can safely return 0 for any operation we decide not to clone.
+Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) {
+ unsigned Opcode = DU.NarrowUse->getOpcode();
+ switch (Opcode) {
+ default:
+ return 0;
+ case Instruction::Add:
+ case Instruction::Mul:
+ case Instruction::UDiv:
+ case Instruction::Sub:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ case Instruction::Shl:
+ case Instruction::LShr:
+ case Instruction::AShr:
+ DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n");
+
+ IRBuilder<> Builder(DU.NarrowUse);
+
+ // Replace NarrowDef operands with WideDef. Otherwise, we don't know
+ // anything about the narrow operand yet so must insert a [sz]ext. It is
+ // probably loop invariant and will be folded or hoisted. If it actually
+ // comes from a widened IV, it should be removed during a future call to
+ // WidenIVUse.
+ Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef :
+ getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, Builder);
+ Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef :
+ getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, Builder);
+
+ BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse);
+ BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(),
+ LHS, RHS,
+ NarrowBO->getName());
+ Builder.Insert(WideBO);
+ if (const OverflowingBinaryOperator *OBO =
+ dyn_cast<OverflowingBinaryOperator>(NarrowBO)) {
+ if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap();
+ if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap();
+ }
+ return WideBO;
}
+ llvm_unreachable(0);
}
-/// ConvertToSInt - Convert APF to an integer, if possible.
-static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) {
- bool isExact = false;
- if (&APF.getSemantics() == &APFloat::PPCDoubleDouble)
+/// HoistStep - Attempt to hoist an IV increment above a potential use.
+///
+/// To successfully hoist, two criteria must be met:
+/// - IncV operands dominate InsertPos and
+/// - InsertPos dominates IncV
+///
+/// Meeting the second condition means that we don't need to check all of IncV's
+/// existing uses (it's moving up in the domtree).
+///
+/// This does not yet recursively hoist the operands, although that would
+/// not be difficult.
+static bool HoistStep(Instruction *IncV, Instruction *InsertPos,
+ const DominatorTree *DT)
+{
+ if (DT->dominates(IncV, InsertPos))
+ return true;
+
+ if (!DT->dominates(InsertPos->getParent(), IncV->getParent()))
return false;
- // See if we can convert this to an int64_t
- uint64_t UIntVal;
- if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero,
- &isExact) != APFloat::opOK || !isExact)
+
+ if (IncV->mayHaveSideEffects())
return false;
- IntVal = UIntVal;
+
+ // Attempt to hoist IncV
+ for (User::op_iterator OI = IncV->op_begin(), OE = IncV->op_end();
+ OI != OE; ++OI) {
+ Instruction *OInst = dyn_cast<Instruction>(OI);
+ if (OInst && !DT->dominates(OInst, InsertPos))
+ return false;
+ }
+ IncV->moveBefore(InsertPos);
return true;
}
-/// HandleFloatingPointIV - If the loop has floating induction variable
-/// then insert corresponding integer induction variable if possible.
-/// For example,
-/// for(double i = 0; i < 10000; ++i)
-/// bar(i)
-/// is converted into
-/// for(int i = 0; i < 10000; ++i)
-/// bar((double)i);
+// GetWideRecurrence - Is this instruction potentially interesting from IVUsers'
+// perspective after widening it's type? In other words, can the extend be
+// safely hoisted out of the loop with SCEV reducing the value to a recurrence
+// on the same loop. If so, return the sign or zero extended
+// recurrence. Otherwise return NULL.
+const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) {
+ if (!SE->isSCEVable(NarrowUse->getType()))
+ return 0;
+
+ const SCEV *NarrowExpr = SE->getSCEV(NarrowUse);
+ if (SE->getTypeSizeInBits(NarrowExpr->getType())
+ >= SE->getTypeSizeInBits(WideType)) {
+ // NarrowUse implicitly widens its operand. e.g. a gep with a narrow
+ // index. So don't follow this use.
+ return 0;
+ }
+
+ const SCEV *WideExpr = IsSigned ?
+ SE->getSignExtendExpr(NarrowExpr, WideType) :
+ SE->getZeroExtendExpr(NarrowExpr, WideType);
+ const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
+ if (!AddRec || AddRec->getLoop() != L)
+ return 0;
+
+ return AddRec;
+}
+
+/// WidenIVUse - Determine whether an individual user of the narrow IV can be
+/// widened. If so, return the wide clone of the user.
+Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU) {
+
+ // Stop traversing the def-use chain at inner-loop phis or post-loop phis.
+ if (isa<PHINode>(DU.NarrowUse) &&
+ LI->getLoopFor(DU.NarrowUse->getParent()) != L)
+ return 0;
+
+ // Our raison d'etre! Eliminate sign and zero extension.
+ if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
+ Value *NewDef = DU.WideDef;
+ if (DU.NarrowUse->getType() != WideType) {
+ unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
+ unsigned IVWidth = SE->getTypeSizeInBits(WideType);
+ if (CastWidth < IVWidth) {
+ // The cast isn't as wide as the IV, so insert a Trunc.
+ IRBuilder<> Builder(DU.NarrowUse);
+ NewDef = Builder.CreateTrunc(DU.WideDef, DU.NarrowUse->getType());
+ }
+ else {
+ // A wider extend was hidden behind a narrower one. This may induce
+ // another round of IV widening in which the intermediate IV becomes
+ // dead. It should be very rare.
+ DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi
+ << " not wide enough to subsume " << *DU.NarrowUse << "\n");
+ DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
+ NewDef = DU.NarrowUse;
+ }
+ }
+ if (NewDef != DU.NarrowUse) {
+ DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse
+ << " replaced by " << *DU.WideDef << "\n");
+ ++NumElimExt;
+ DU.NarrowUse->replaceAllUsesWith(NewDef);
+ DeadInsts.push_back(DU.NarrowUse);
+ }
+ // Now that the extend is gone, we want to expose it's uses for potential
+ // further simplification. We don't need to directly inform SimplifyIVUsers
+ // of the new users, because their parent IV will be processed later as a
+ // new loop phi. If we preserved IVUsers analysis, we would also want to
+ // push the uses of WideDef here.
+
+ // No further widening is needed. The deceased [sz]ext had done it for us.
+ return 0;
+ }
+
+ // Does this user itself evaluate to a recurrence after widening?
+ const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse);
+ if (!WideAddRec) {
+ // This user does not evaluate to a recurence after widening, so don't
+ // follow it. Instead insert a Trunc to kill off the original use,
+ // eventually isolating the original narrow IV so it can be removed.
+ IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
+ Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
+ DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
+ return 0;
+ }
+ // Assume block terminators cannot evaluate to a recurrence. We can't to
+ // insert a Trunc after a terminator if there happens to be a critical edge.
+ assert(DU.NarrowUse != DU.NarrowUse->getParent()->getTerminator() &&
+ "SCEV is not expected to evaluate a block terminator");
+
+ // Reuse the IV increment that SCEVExpander created as long as it dominates
+ // NarrowUse.
+ Instruction *WideUse = 0;
+ if (WideAddRec == WideIncExpr && HoistStep(WideInc, DU.NarrowUse, DT)) {
+ WideUse = WideInc;
+ }
+ else {
+ WideUse = CloneIVUser(DU);
+ if (!WideUse)
+ return 0;
+ }
+ // Evaluation of WideAddRec ensured that the narrow expression could be
+ // extended outside the loop without overflow. This suggests that the wide use
+ // evaluates to the same expression as the extended narrow use, but doesn't
+ // absolutely guarantee it. Hence the following failsafe check. In rare cases
+ // where it fails, we simply throw away the newly created wide use.
+ if (WideAddRec != SE->getSCEV(WideUse)) {
+ DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
+ << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
+ DeadInsts.push_back(WideUse);
+ return 0;
+ }
+
+ // Returning WideUse pushes it on the worklist.
+ return WideUse;
+}
+
+/// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers.
///
-void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
- unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
- unsigned BackEdge = IncomingEdge^1;
+void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
+ for (Value::use_iterator UI = NarrowDef->use_begin(),
+ UE = NarrowDef->use_end(); UI != UE; ++UI) {
+ Instruction *NarrowUse = cast<Instruction>(*UI);
- // Check incoming value.
- ConstantFP *InitValueVal =
- dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
+ // Handle data flow merges and bizarre phi cycles.
+ if (!Widened.insert(NarrowUse))
+ continue;
- int64_t InitValue;
- if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
- return;
+ NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUse, WideDef));
+ }
+}
- // Check IV increment. Reject this PN if increment operation is not
- // an add or increment value can not be represented by an integer.
- BinaryOperator *Incr =
- dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge));
- if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return;
-
- // If this is not an add of the PHI with a constantfp, or if the constant fp
- // is not an integer, bail out.
- ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1));
- int64_t IncValue;
- if (IncValueVal == 0 || Incr->getOperand(0) != PN ||
- !ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
- return;
+/// CreateWideIV - Process a single induction variable. First use the
+/// SCEVExpander to create a wide induction variable that evaluates to the same
+/// recurrence as the original narrow IV. Then use a worklist to forward
+/// traverse the narrow IV's def-use chain. After WidenIVUse has processed all
+/// interesting IV users, the narrow IV will be isolated for removal by
+/// DeleteDeadPHIs.
+///
+/// It would be simpler to delete uses as they are processed, but we must avoid
+/// invalidating SCEV expressions.
+///
+PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) {
+ // Is this phi an induction variable?
+ const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
+ if (!AddRec)
+ return NULL;
+
+ // Widen the induction variable expression.
+ const SCEV *WideIVExpr = IsSigned ?
+ SE->getSignExtendExpr(AddRec, WideType) :
+ SE->getZeroExtendExpr(AddRec, WideType);
+
+ assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType &&
+ "Expect the new IV expression to preserve its type");
+
+ // Can the IV be extended outside the loop without overflow?
+ AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
+ if (!AddRec || AddRec->getLoop() != L)
+ return NULL;
+
+ // An AddRec must have loop-invariant operands. Since this AddRec is
+ // materialized by a loop header phi, the expression cannot have any post-loop
+ // operands, so they must dominate the loop header.
+ assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) &&
+ SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader())
+ && "Loop header phi recurrence inputs do not dominate the loop");
+
+ // The rewriter provides a value for the desired IV expression. This may
+ // either find an existing phi or materialize a new one. Either way, we
+ // expect a well-formed cyclic phi-with-increments. i.e. any operand not part
+ // of the phi-SCC dominates the loop entry.
+ Instruction *InsertPt = L->getHeader()->begin();
+ WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
+
+ // Remembering the WideIV increment generated by SCEVExpander allows
+ // WidenIVUse to reuse it when widening the narrow IV's increment. We don't
+ // employ a general reuse mechanism because the call above is the only call to
+ // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses.
+ if (BasicBlock *LatchBlock = L->getLoopLatch()) {
+ WideInc =
+ cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock));
+ WideIncExpr = SE->getSCEV(WideInc);
+ }
- // Check Incr uses. One user is PN and the other user is an exit condition
- // used by the conditional terminator.
- Value::use_iterator IncrUse = Incr->use_begin();
- Instruction *U1 = cast<Instruction>(IncrUse++);
- if (IncrUse == Incr->use_end()) return;
- Instruction *U2 = cast<Instruction>(IncrUse++);
- if (IncrUse != Incr->use_end()) return;
+ DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n");
+ ++NumWidened;
- // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't
- // only used by a branch, we can't transform it.
- FCmpInst *Compare = dyn_cast<FCmpInst>(U1);
- if (!Compare)
- Compare = dyn_cast<FCmpInst>(U2);
- if (Compare == 0 || !Compare->hasOneUse() ||
- !isa<BranchInst>(Compare->use_back()))
- return;
-
- BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
+ // Traverse the def-use chain using a worklist starting at the original IV.
+ assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" );
- // We need to verify that the branch actually controls the iteration count
- // of the loop. If not, the new IV can overflow and no one will notice.
- // The branch block must be in the loop and one of the successors must be out
- // of the loop.
- assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
- if (!L->contains(TheBr->getParent()) ||
- (L->contains(TheBr->getSuccessor(0)) &&
- L->contains(TheBr->getSuccessor(1))))
- return;
-
-
- // If it isn't a comparison with an integer-as-fp (the exit value), we can't
- // transform it.
- ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
- int64_t ExitValue;
- if (ExitValueVal == 0 ||
- !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
- return;
-
- // Find new predicate for integer comparison.
- CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE;
- switch (Compare->getPredicate()) {
- default: return; // Unknown comparison.
- case CmpInst::FCMP_OEQ:
- case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break;
- case CmpInst::FCMP_ONE:
- case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break;
- case CmpInst::FCMP_OGT:
- case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
- case CmpInst::FCMP_OGE:
- case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
- case CmpInst::FCMP_OLT:
- case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
- case CmpInst::FCMP_OLE:
- case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
+ Widened.insert(OrigPhi);
+ pushNarrowIVUsers(OrigPhi, WidePhi);
+
+ while (!NarrowIVUsers.empty()) {
+ NarrowIVDefUse DU = NarrowIVUsers.pop_back_val();
+
+ // Process a def-use edge. This may replace the use, so don't hold a
+ // use_iterator across it.
+ Instruction *WideUse = WidenIVUse(DU);
+
+ // Follow all def-use edges from the previous narrow use.
+ if (WideUse)
+ pushNarrowIVUsers(DU.NarrowUse, WideUse);
+
+ // WidenIVUse may have removed the def-use edge.
+ if (DU.NarrowDef->use_empty())
+ DeadInsts.push_back(DU.NarrowDef);
}
-
- // We convert the floating point induction variable to a signed i32 value if
- // we can. This is only safe if the comparison will not overflow in a way
- // that won't be trapped by the integer equivalent operations. Check for this
- // now.
- // TODO: We could use i64 if it is native and the range requires it.
-
- // The start/stride/exit values must all fit in signed i32.
- if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue))
- return;
+ return WidePhi;
+}
- // If not actually striding (add x, 0.0), avoid touching the code.
- if (IncValue == 0)
+//===----------------------------------------------------------------------===//
+// Simplification of IV users based on SCEV evaluation.
+//===----------------------------------------------------------------------===//
+
+void IndVarSimplify::EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
+ unsigned IVOperIdx = 0;
+ ICmpInst::Predicate Pred = ICmp->getPredicate();
+ if (IVOperand != ICmp->getOperand(0)) {
+ // Swapped
+ assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
+ IVOperIdx = 1;
+ Pred = ICmpInst::getSwappedPredicate(Pred);
+ }
+
+ // Get the SCEVs for the ICmp operands.
+ const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx));
+ const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx));
+
+ // Simplify unnecessary loops away.
+ const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
+ S = SE->getSCEVAtScope(S, ICmpLoop);
+ X = SE->getSCEVAtScope(X, ICmpLoop);
+
+ // If the condition is always true or always false, replace it with
+ // a constant value.
+ if (SE->isKnownPredicate(Pred, S, X))
+ ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
+ else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
+ ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
+ else
return;
- // Positive and negative strides have different safety conditions.
- if (IncValue > 0) {
- // If we have a positive stride, we require the init to be less than the
- // exit value and an equality or less than comparison.
- if (InitValue >= ExitValue ||
- NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE)
- return;
-
- uint32_t Range = uint32_t(ExitValue-InitValue);
- if (NewPred == CmpInst::ICMP_SLE) {
- // Normalize SLE -> SLT, check for infinite loop.
- if (++Range == 0) return; // Range overflows.
- }
-
- unsigned Leftover = Range % uint32_t(IncValue);
-
- // If this is an equality comparison, we require that the strided value
- // exactly land on the exit value, otherwise the IV condition will wrap
- // around and do things the fp IV wouldn't.
- if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
- Leftover != 0)
+ DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
+ ++NumElimCmp;
+ Changed = true;
+ DeadInsts.push_back(ICmp);
+}
+
+void IndVarSimplify::EliminateIVRemainder(BinaryOperator *Rem,
+ Value *IVOperand,
+ bool IsSigned) {
+ // We're only interested in the case where we know something about
+ // the numerator.
+ if (IVOperand != Rem->getOperand(0))
+ return;
+
+ // Get the SCEVs for the ICmp operands.
+ const SCEV *S = SE->getSCEV(Rem->getOperand(0));
+ const SCEV *X = SE->getSCEV(Rem->getOperand(1));
+
+ // Simplify unnecessary loops away.
+ const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
+ S = SE->getSCEVAtScope(S, ICmpLoop);
+ X = SE->getSCEVAtScope(X, ICmpLoop);
+
+ // i % n --> i if i is in [0,n).
+ if ((!IsSigned || SE->isKnownNonNegative(S)) &&
+ SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ S, X))
+ Rem->replaceAllUsesWith(Rem->getOperand(0));
+ else {
+ // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
+ const SCEV *LessOne =
+ SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
+ if (IsSigned && !SE->isKnownNonNegative(LessOne))
return;
-
- // If the stride would wrap around the i32 before exiting, we can't
- // transform the IV.
- if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue)
+
+ if (!SE->isKnownPredicate(IsSigned ?
+ ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ LessOne, X))
return;
-
+
+ ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
+ Rem->getOperand(0), Rem->getOperand(1),
+ "tmp");
+ SelectInst *Sel =
+ SelectInst::Create(ICmp,
+ ConstantInt::get(Rem->getType(), 0),
+ Rem->getOperand(0), "tmp", Rem);
+ Rem->replaceAllUsesWith(Sel);
+ }
+
+ // Inform IVUsers about the new users.
+ if (IU) {
+ if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
+ IU->AddUsersIfInteresting(I);
+ }
+ DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
+ ++NumElimRem;
+ Changed = true;
+ DeadInsts.push_back(Rem);
+}
+
+/// EliminateIVUser - Eliminate an operation that consumes a simple IV and has
+/// no observable side-effect given the range of IV values.
+bool IndVarSimplify::EliminateIVUser(Instruction *UseInst,
+ Instruction *IVOperand) {
+ if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
+ EliminateIVComparison(ICmp, IVOperand);
+ return true;
+ }
+ if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
+ bool IsSigned = Rem->getOpcode() == Instruction::SRem;
+ if (IsSigned || Rem->getOpcode() == Instruction::URem) {
+ EliminateIVRemainder(Rem, IVOperand, IsSigned);
+ return true;
+ }
+ }
+
+ // Eliminate any operation that SCEV can prove is an identity function.
+ if (!SE->isSCEVable(UseInst->getType()) ||
+ (UseInst->getType() != IVOperand->getType()) ||
+ (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand)))
+ return false;
+
+ DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');
+
+ UseInst->replaceAllUsesWith(IVOperand);
+ ++NumElimIdentity;
+ Changed = true;
+ DeadInsts.push_back(UseInst);
+ return true;
+}
+
+/// pushIVUsers - Add all uses of Def to the current IV's worklist.
+///
+static void pushIVUsers(
+ Instruction *Def,
+ SmallPtrSet<Instruction*,16> &Simplified,
+ SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) {
+
+ for (Value::use_iterator UI = Def->use_begin(), E = Def->use_end();
+ UI != E; ++UI) {
+ Instruction *User = cast<Instruction>(*UI);
+
+ // Avoid infinite or exponential worklist processing.
+ // Also ensure unique worklist users.
+ // If Def is a LoopPhi, it may not be in the Simplified set, so check for
+ // self edges first.
+ if (User != Def && Simplified.insert(User))
+ SimpleIVUsers.push_back(std::make_pair(User, Def));
+ }
+}
+
+/// isSimpleIVUser - Return true if this instruction generates a simple SCEV
+/// expression in terms of that IV.
+///
+/// This is similar to IVUsers' isInsteresting() but processes each instruction
+/// non-recursively when the operand is already known to be a simpleIVUser.
+///
+static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) {
+ if (!SE->isSCEVable(I->getType()))
+ return false;
+
+ // Get the symbolic expression for this instruction.
+ const SCEV *S = SE->getSCEV(I);
+
+ // Only consider affine recurrences.
+ const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S);
+ if (AR && AR->getLoop() == L)
+ return true;
+
+ return false;
+}
+
+/// SimplifyIVUsersNoRewrite - Iteratively perform simplification on a worklist
+/// of IV users. Each successive simplification may push more users which may
+/// themselves be candidates for simplification.
+///
+/// The "NoRewrite" algorithm does not require IVUsers analysis. Instead, it
+/// simplifies instructions in-place during analysis. Rather than rewriting
+/// induction variables bottom-up from their users, it transforms a chain of
+/// IVUsers top-down, updating the IR only when it encouters a clear
+/// optimization opportunitiy. A SCEVExpander "Rewriter" instance is still
+/// needed, but only used to generate a new IV (phi) of wider type for sign/zero
+/// extend elimination.
+///
+/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers.
+///
+void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) {
+ std::map<PHINode *, WideIVInfo> WideIVMap;
+
+ SmallVector<PHINode*, 8> LoopPhis;
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
+ LoopPhis.push_back(cast<PHINode>(I));
+ }
+ // Each round of simplification iterates through the SimplifyIVUsers worklist
+ // for all current phis, then determines whether any IVs can be
+ // widened. Widening adds new phis to LoopPhis, inducing another round of
+ // simplification on the wide IVs.
+ while (!LoopPhis.empty()) {
+ // Evaluate as many IV expressions as possible before widening any IVs. This
+ // forces SCEV to set no-wrap flags before evaluating sign/zero
+ // extension. The first time SCEV attempts to normalize sign/zero extension,
+ // the result becomes final. So for the most predictable results, we delay
+ // evaluation of sign/zero extend evaluation until needed, and avoid running
+ // other SCEV based analysis prior to SimplifyIVUsersNoRewrite.
+ do {
+ PHINode *CurrIV = LoopPhis.pop_back_val();
+
+ // Information about sign/zero extensions of CurrIV.
+ WideIVInfo WI;
+
+ // Instructions processed by SimplifyIVUsers for CurrIV.
+ SmallPtrSet<Instruction*,16> Simplified;
+
+ // Use-def pairs if IV users waiting to be processed for CurrIV.
+ SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;
+
+ // Push users of the current LoopPhi. In rare cases, pushIVUsers may be
+ // called multiple times for the same LoopPhi. This is the proper thing to
+ // do for loop header phis that use each other.
+ pushIVUsers(CurrIV, Simplified, SimpleIVUsers);
+
+ while (!SimpleIVUsers.empty()) {
+ std::pair<Instruction*, Instruction*> UseOper =
+ SimpleIVUsers.pop_back_val();
+ // Bypass back edges to avoid extra work.
+ if (UseOper.first == CurrIV) continue;
+
+ if (EliminateIVUser(UseOper.first, UseOper.second)) {
+ pushIVUsers(UseOper.second, Simplified, SimpleIVUsers);
+ continue;
+ }
+ if (CastInst *Cast = dyn_cast<CastInst>(UseOper.first)) {
+ bool IsSigned = Cast->getOpcode() == Instruction::SExt;
+ if (IsSigned || Cast->getOpcode() == Instruction::ZExt) {
+ CollectExtend(Cast, IsSigned, WI, SE, TD);
+ }
+ continue;
+ }
+ if (isSimpleIVUser(UseOper.first, L, SE)) {
+ pushIVUsers(UseOper.first, Simplified, SimpleIVUsers);
+ }
+ }
+ if (WI.WidestNativeType) {
+ WideIVMap[CurrIV] = WI;
+ }
+ } while(!LoopPhis.empty());
+
+ for (std::map<PHINode *, WideIVInfo>::const_iterator I = WideIVMap.begin(),
+ E = WideIVMap.end(); I != E; ++I) {
+ WidenIV Widener(I->first, I->second, LI, SE, DT, DeadInsts);
+ if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) {
+ Changed = true;
+ LoopPhis.push_back(WidePhi);
+ }
+ }
+ WideIVMap.clear();
+ }
+}
+
+/// SimplifyCongruentIVs - Check for congruent phis in this loop header and
+/// populate ExprToIVMap for use later.
+///
+void IndVarSimplify::SimplifyCongruentIVs(Loop *L) {
+ DenseMap<const SCEV *, PHINode *> ExprToIVMap;
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
+ PHINode *Phi = cast<PHINode>(I);
+ if (!SE->isSCEVable(Phi->getType()))
+ continue;
+
+ const SCEV *S = SE->getSCEV(Phi);
+ std::pair<DenseMap<const SCEV *, PHINode *>::const_iterator, bool> Tmp =
+ ExprToIVMap.insert(std::make_pair(S, Phi));
+ if (Tmp.second)
+ continue;
+ PHINode *OrigPhi = Tmp.first->second;
+
+ // If one phi derives from the other via GEPs, types may differ.
+ if (OrigPhi->getType() != Phi->getType())
+ continue;
+
+ // Replacing the congruent phi is sufficient because acyclic redundancy
+ // elimination, CSE/GVN, should handle the rest. However, once SCEV proves
+ // that a phi is congruent, it's almost certain to be the head of an IV
+ // user cycle that is isomorphic with the original phi. So it's worth
+ // eagerly cleaning up the common case of a single IV increment.
+ if (BasicBlock *LatchBlock = L->getLoopLatch()) {
+ Instruction *OrigInc =
+ cast<Instruction>(OrigPhi->getIncomingValueForBlock(LatchBlock));
+ Instruction *IsomorphicInc =
+ cast<Instruction>(Phi->getIncomingValueForBlock(LatchBlock));
+ if (OrigInc != IsomorphicInc &&
+ OrigInc->getType() == IsomorphicInc->getType() &&
+ SE->getSCEV(OrigInc) == SE->getSCEV(IsomorphicInc) &&
+ HoistStep(OrigInc, IsomorphicInc, DT)) {
+ DEBUG(dbgs() << "INDVARS: Eliminated congruent iv.inc: "
+ << *IsomorphicInc << '\n');
+ IsomorphicInc->replaceAllUsesWith(OrigInc);
+ DeadInsts.push_back(IsomorphicInc);
+ }
+ }
+ DEBUG(dbgs() << "INDVARS: Eliminated congruent iv: " << *Phi << '\n');
+ ++NumElimIV;
+ Phi->replaceAllUsesWith(OrigPhi);
+ DeadInsts.push_back(Phi);
+ }
+}
+
+//===----------------------------------------------------------------------===//
+// LinearFunctionTestReplace and its kin. Rewrite the loop exit condition.
+//===----------------------------------------------------------------------===//
+
+// Check for expressions that ScalarEvolution generates to compute
+// BackedgeTakenInfo. If these expressions have not been reduced, then expanding
+// them may incur additional cost (albeit in the loop preheader).
+static bool isHighCostExpansion(const SCEV *S, BranchInst *BI,
+ ScalarEvolution *SE) {
+ // If the backedge-taken count is a UDiv, it's very likely a UDiv that
+ // ScalarEvolution's HowFarToZero or HowManyLessThans produced to compute a
+ // precise expression, rather than a UDiv from the user's code. If we can't
+ // find a UDiv in the code with some simple searching, assume the former and
+ // forego rewriting the loop.
+ if (isa<SCEVUDivExpr>(S)) {
+ ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!OrigCond) return true;
+ const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
+ R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
+ if (R != S) {
+ const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
+ L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
+ if (L != S)
+ return true;
+ }
+ }
+
+ if (!DisableIVRewrite || ForceLFTR)
+ return false;
+
+ // Recurse past add expressions, which commonly occur in the
+ // BackedgeTakenCount. They may already exist in program code, and if not,
+ // they are not too expensive rematerialize.
+ if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
+ for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
+ I != E; ++I) {
+ if (isHighCostExpansion(*I, BI, SE))
+ return true;
+ }
+ return false;
+ }
+
+ // HowManyLessThans uses a Max expression whenever the loop is not guarded by
+ // the exit condition.
+ if (isa<SCEVSMaxExpr>(S) || isa<SCEVUMaxExpr>(S))
+ return true;
+
+ // If we haven't recognized an expensive SCEV patter, assume its an expression
+ // produced by program code.
+ return false;
+}
+
+/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken
+/// count expression can be safely and cheaply expanded into an instruction
+/// sequence that can be used by LinearFunctionTestReplace.
+static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) {
+ const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
+ if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
+ BackedgeTakenCount->isZero())
+ return false;
+
+ if (!L->getExitingBlock())
+ return false;
+
+ // Can't rewrite non-branch yet.
+ BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
+ if (!BI)
+ return false;
+
+ if (isHighCostExpansion(BackedgeTakenCount, BI, SE))
+ return false;
+
+ return true;
+}
+
+/// getBackedgeIVType - Get the widest type used by the loop test after peeking
+/// through Truncs.
+///
+/// TODO: Unnecessary when ForceLFTR is removed.
+static Type *getBackedgeIVType(Loop *L) {
+ if (!L->getExitingBlock())
+ return 0;
+
+ // Can't rewrite non-branch yet.
+ BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
+ if (!BI)
+ return 0;
+
+ ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!Cond)
+ return 0;
+
+ Type *Ty = 0;
+ for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end();
+ OI != OE; ++OI) {
+ assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types");
+ TruncInst *Trunc = dyn_cast<TruncInst>(*OI);
+ if (!Trunc)
+ continue;
+
+ return Trunc->getSrcTy();
+ }
+ return Ty;
+}
+
+/// isLoopInvariant - Perform a quick domtree based check for loop invariance
+/// assuming that V is used within the loop. LoopInfo::isLoopInvariant() seems
+/// gratuitous for this purpose.
+static bool isLoopInvariant(Value *V, Loop *L, DominatorTree *DT) {
+ Instruction *Inst = dyn_cast<Instruction>(V);
+ if (!Inst)
+ return true;
+
+ return DT->properlyDominates(Inst->getParent(), L->getHeader());
+}
+
+/// getLoopPhiForCounter - Return the loop header phi IFF IncV adds a loop
+/// invariant value to the phi.
+static PHINode *getLoopPhiForCounter(Value *IncV, Loop *L, DominatorTree *DT) {
+ Instruction *IncI = dyn_cast<Instruction>(IncV);
+ if (!IncI)
+ return 0;
+
+ switch (IncI->getOpcode()) {
+ case Instruction::Add:
+ case Instruction::Sub:
+ break;
+ case Instruction::GetElementPtr:
+ // An IV counter must preserve its type.
+ if (IncI->getNumOperands() == 2)
+ break;
+ default:
+ return 0;
+ }
+
+ PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0));
+ if (Phi && Phi->getParent() == L->getHeader()) {
+ if (isLoopInvariant(IncI->getOperand(1), L, DT))
+ return Phi;
+ return 0;
+ }
+ if (IncI->getOpcode() == Instruction::GetElementPtr)
+ return 0;
+
+ // Allow add/sub to be commuted.
+ Phi = dyn_cast<PHINode>(IncI->getOperand(1));
+ if (Phi && Phi->getParent() == L->getHeader()) {
+ if (isLoopInvariant(IncI->getOperand(0), L, DT))
+ return Phi;
+ }
+ return 0;
+}
+
+/// needsLFTR - LinearFunctionTestReplace policy. Return true unless we can show
+/// that the current exit test is already sufficiently canonical.
+static bool needsLFTR(Loop *L, DominatorTree *DT) {
+ assert(L->getExitingBlock() && "expected loop exit");
+
+ BasicBlock *LatchBlock = L->getLoopLatch();
+ // Don't bother with LFTR if the loop is not properly simplified.
+ if (!LatchBlock)
+ return false;
+
+ BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
+ assert(BI && "expected exit branch");
+
+ // Do LFTR to simplify the exit condition to an ICMP.
+ ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!Cond)
+ return true;
+
+ // Do LFTR to simplify the exit ICMP to EQ/NE
+ ICmpInst::Predicate Pred = Cond->getPredicate();
+ if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
+ return true;
+
+ // Look for a loop invariant RHS
+ Value *LHS = Cond->getOperand(0);
+ Value *RHS = Cond->getOperand(1);
+ if (!isLoopInvariant(RHS, L, DT)) {
+ if (!isLoopInvariant(LHS, L, DT))
+ return true;
+ std::swap(LHS, RHS);
+ }
+ // Look for a simple IV counter LHS
+ PHINode *Phi = dyn_cast<PHINode>(LHS);
+ if (!Phi)
+ Phi = getLoopPhiForCounter(LHS, L, DT);
+
+ if (!Phi)
+ return true;
+
+ // Do LFTR if the exit condition's IV is *not* a simple counter.
+ Value *IncV = Phi->getIncomingValueForBlock(L->getLoopLatch());
+ return Phi != getLoopPhiForCounter(IncV, L, DT);
+}
+
+/// AlmostDeadIV - Return true if this IV has any uses other than the (soon to
+/// be rewritten) loop exit test.
+static bool AlmostDeadIV(PHINode *Phi, BasicBlock *LatchBlock, Value *Cond) {
+ int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
+ Value *IncV = Phi->getIncomingValue(LatchIdx);
+
+ for (Value::use_iterator UI = Phi->use_begin(), UE = Phi->use_end();
+ UI != UE; ++UI) {
+ if (*UI != Cond && *UI != IncV) return false;
+ }
+
+ for (Value::use_iterator UI = IncV->use_begin(), UE = IncV->use_end();
+ UI != UE; ++UI) {
+ if (*UI != Cond && *UI != Phi) return false;
+ }
+ return true;
+}
+
+/// FindLoopCounter - Find an affine IV in canonical form.
+///
+/// FIXME: Accept -1 stride and set IVLimit = IVInit - BECount
+///
+/// FIXME: Accept non-unit stride as long as SCEV can reduce BECount * Stride.
+/// This is difficult in general for SCEV because of potential overflow. But we
+/// could at least handle constant BECounts.
+static PHINode *
+FindLoopCounter(Loop *L, const SCEV *BECount,
+ ScalarEvolution *SE, DominatorTree *DT, const TargetData *TD) {
+ // I'm not sure how BECount could be a pointer type, but we definitely don't
+ // want to LFTR that.
+ if (BECount->getType()->isPointerTy())
+ return 0;
+
+ uint64_t BCWidth = SE->getTypeSizeInBits(BECount->getType());
+
+ Value *Cond =
+ cast<BranchInst>(L->getExitingBlock()->getTerminator())->getCondition();
+
+ // Loop over all of the PHI nodes, looking for a simple counter.
+ PHINode *BestPhi = 0;
+ const SCEV *BestInit = 0;
+ BasicBlock *LatchBlock = L->getLoopLatch();
+ assert(LatchBlock && "needsLFTR should guarantee a loop latch");
+
+ for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
+ PHINode *Phi = cast<PHINode>(I);
+ if (!SE->isSCEVable(Phi->getType()))
+ continue;
+
+ const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
+ if (!AR || AR->getLoop() != L || !AR->isAffine())
+ continue;
+
+ // AR may be a pointer type, while BECount is an integer type.
+ // AR may be wider than BECount. With eq/ne tests overflow is immaterial.
+ // AR may not be a narrower type, or we may never exit.
+ uint64_t PhiWidth = SE->getTypeSizeInBits(AR->getType());
+ if (PhiWidth < BCWidth || (TD && !TD->isLegalInteger(PhiWidth)))
+ continue;
+
+ const SCEV *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE));
+ if (!Step || !Step->isOne())
+ continue;
+
+ int LatchIdx = Phi->getBasicBlockIndex(LatchBlock);
+ Value *IncV = Phi->getIncomingValue(LatchIdx);
+ if (getLoopPhiForCounter(IncV, L, DT) != Phi)
+ continue;
+
+ const SCEV *Init = AR->getStart();
+
+ if (BestPhi && !AlmostDeadIV(BestPhi, LatchBlock, Cond)) {
+ // Don't force a live loop counter if another IV can be used.
+ if (AlmostDeadIV(Phi, LatchBlock, Cond))
+ continue;
+
+ // Prefer to count-from-zero. This is a more "canonical" counter form. It
+ // also prefers integer to pointer IVs.
+ if (BestInit->isZero() != Init->isZero()) {
+ if (BestInit->isZero())
+ continue;
+ }
+ // If two IVs both count from zero or both count from nonzero then the
+ // narrower is likely a dead phi that has been widened. Use the wider phi
+ // to allow the other to be eliminated.
+ if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
+ continue;
+ }
+ BestPhi = Phi;
+ BestInit = Init;
+ }
+ return BestPhi;
+}
+
+/// LinearFunctionTestReplace - This method rewrites the exit condition of the
+/// loop to be a canonical != comparison against the incremented loop induction
+/// variable. This pass is able to rewrite the exit tests of any loop where the
+/// SCEV analysis can determine a loop-invariant trip count of the loop, which
+/// is actually a much broader range than just linear tests.
+Value *IndVarSimplify::
+LinearFunctionTestReplace(Loop *L,
+ const SCEV *BackedgeTakenCount,
+ PHINode *IndVar,
+ SCEVExpander &Rewriter) {
+ assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
+ BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
+
+ // In DisableIVRewrite mode, IndVar is not necessarily a canonical IV. In this
+ // mode, LFTR can ignore IV overflow and truncate to the width of
+ // BECount. This avoids materializing the add(zext(add)) expression.
+ Type *CntTy = DisableIVRewrite ?
+ BackedgeTakenCount->getType() : IndVar->getType();
+
+ const SCEV *IVLimit = BackedgeTakenCount;
+
+ // If the exiting block is not the same as the backedge block, we must compare
+ // against the preincremented value, otherwise we prefer to compare against
+ // the post-incremented value.
+ Value *CmpIndVar;
+ if (L->getExitingBlock() == L->getLoopLatch()) {
+ // Add one to the "backedge-taken" count to get the trip count.
+ // If this addition may overflow, we have to be more pessimistic and
+ // cast the induction variable before doing the add.
+ const SCEV *N =
+ SE->getAddExpr(IVLimit, SE->getConstant(IVLimit->getType(), 1));
+ if (CntTy == IVLimit->getType())
+ IVLimit = N;
+ else {
+ const SCEV *Zero = SE->getConstant(IVLimit->getType(), 0);
+ if ((isa<SCEVConstant>(N) && !N->isZero()) ||
+ SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
+ // No overflow. Cast the sum.
+ IVLimit = SE->getTruncateOrZeroExtend(N, CntTy);
+ } else {
+ // Potential overflow. Cast before doing the add.
+ IVLimit = SE->getTruncateOrZeroExtend(IVLimit, CntTy);
+ IVLimit = SE->getAddExpr(IVLimit, SE->getConstant(CntTy, 1));
+ }
+ }
+ // The BackedgeTaken expression contains the number of times that the
+ // backedge branches to the loop header. This is one less than the
+ // number of times the loop executes, so use the incremented indvar.
+ CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock());
} else {
- // If we have a negative stride, we require the init to be greater than the
- // exit value and an equality or greater than comparison.
- if (InitValue >= ExitValue ||
- NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE)
- return;
-
- uint32_t Range = uint32_t(InitValue-ExitValue);
- if (NewPred == CmpInst::ICMP_SGE) {
- // Normalize SGE -> SGT, check for infinite loop.
- if (++Range == 0) return; // Range overflows.
+ // We have to use the preincremented value...
+ IVLimit = SE->getTruncateOrZeroExtend(IVLimit, CntTy);
+ CmpIndVar = IndVar;
+ }
+
+ // For unit stride, IVLimit = Start + BECount with 2's complement overflow.
+ // So for, non-zero start compute the IVLimit here.
+ bool isPtrIV = false;
+ Type *CmpTy = CntTy;
+ const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
+ assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter");
+ if (!AR->getStart()->isZero()) {
+ assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride");
+ const SCEV *IVInit = AR->getStart();
+
+ // For pointer types, sign extend BECount in order to materialize a GEP.
+ // Note that for DisableIVRewrite, we never run SCEVExpander on a
+ // pointer type, because we must preserve the existing GEPs. Instead we
+ // directly generate a GEP later.
+ if (IVInit->getType()->isPointerTy()) {
+ isPtrIV = true;
+ CmpTy = SE->getEffectiveSCEVType(IVInit->getType());
+ IVLimit = SE->getTruncateOrSignExtend(IVLimit, CmpTy);
+ }
+ // For integer types, truncate the IV before computing IVInit + BECount.
+ else {
+ if (SE->getTypeSizeInBits(IVInit->getType())
+ > SE->getTypeSizeInBits(CmpTy))
+ IVInit = SE->getTruncateExpr(IVInit, CmpTy);
+
+ IVLimit = SE->getAddExpr(IVInit, IVLimit);
}
-
- unsigned Leftover = Range % uint32_t(-IncValue);
-
- // If this is an equality comparison, we require that the strided value
- // exactly land on the exit value, otherwise the IV condition will wrap
- // around and do things the fp IV wouldn't.
- if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) &&
- Leftover != 0)
- return;
-
- // If the stride would wrap around the i32 before exiting, we can't
- // transform the IV.
- if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue)
- return;
}
-
- const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
+ // Expand the code for the iteration count.
+ IRBuilder<> Builder(BI);
- // Insert new integer induction variable.
- PHINode *NewPHI = PHINode::Create(Int32Ty, PN->getName()+".int", PN);
- NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue),
- PN->getIncomingBlock(IncomingEdge));
+ assert(SE->isLoopInvariant(IVLimit, L) &&
+ "Computed iteration count is not loop invariant!");
+ Value *ExitCnt = Rewriter.expandCodeFor(IVLimit, CmpTy, BI);
+
+ // Create a gep for IVInit + IVLimit from on an existing pointer base.
+ assert(isPtrIV == IndVar->getType()->isPointerTy() &&
+ "IndVar type must match IVInit type");
+ if (isPtrIV) {
+ Value *IVStart = IndVar->getIncomingValueForBlock(L->getLoopPreheader());
+ assert(AR->getStart() == SE->getSCEV(IVStart) && "bad loop counter");
+ assert(SE->getSizeOfExpr(
+ cast<PointerType>(IVStart->getType())->getElementType())->isOne()
+ && "unit stride pointer IV must be i8*");
+
+ Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
+ ExitCnt = Builder.CreateGEP(IVStart, ExitCnt, "lftr.limit");
+ Builder.SetInsertPoint(BI);
+ }
- Value *NewAdd =
- BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue),
- Incr->getName()+".int", Incr);
- NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge));
+ // Insert a new icmp_ne or icmp_eq instruction before the branch.
+ ICmpInst::Predicate P;
+ if (L->contains(BI->getSuccessor(0)))
+ P = ICmpInst::ICMP_NE;
+ else
+ P = ICmpInst::ICMP_EQ;
- ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd,
- ConstantInt::get(Int32Ty, ExitValue),
- Compare->getName());
+ DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
+ << " LHS:" << *CmpIndVar << '\n'
+ << " op:\t"
+ << (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
+ << " RHS:\t" << *ExitCnt << "\n"
+ << " Expr:\t" << *IVLimit << "\n");
- // In the following deletions, PN may become dead and may be deleted.
- // Use a WeakVH to observe whether this happens.
- WeakVH WeakPH = PN;
+ if (SE->getTypeSizeInBits(CmpIndVar->getType())
+ > SE->getTypeSizeInBits(CmpTy)) {
+ CmpIndVar = Builder.CreateTrunc(CmpIndVar, CmpTy, "lftr.wideiv");
+ }
- // Delete the old floating point exit comparison. The branch starts using the
- // new comparison.
- NewCompare->takeName(Compare);
- Compare->replaceAllUsesWith(NewCompare);
- RecursivelyDeleteTriviallyDeadInstructions(Compare);
+ Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
+ Value *OrigCond = BI->getCondition();
+ // It's tempting to use replaceAllUsesWith here to fully replace the old
+ // comparison, but that's not immediately safe, since users of the old
+ // comparison may not be dominated by the new comparison. Instead, just
+ // update the branch to use the new comparison; in the common case this
+ // will make old comparison dead.
+ BI->setCondition(Cond);
+ DeadInsts.push_back(OrigCond);
- // Delete the old floating point increment.
- Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
- RecursivelyDeleteTriviallyDeadInstructions(Incr);
+ ++NumLFTR;
+ Changed = true;
+ return Cond;
+}
- // If the FP induction variable still has uses, this is because something else
- // in the loop uses its value. In order to canonicalize the induction
- // variable, we chose to eliminate the IV and rewrite it in terms of an
- // int->fp cast.
+//===----------------------------------------------------------------------===//
+// SinkUnusedInvariants. A late subpass to cleanup loop preheaders.
+//===----------------------------------------------------------------------===//
+
+/// If there's a single exit block, sink any loop-invariant values that
+/// were defined in the preheader but not used inside the loop into the
+/// exit block to reduce register pressure in the loop.
+void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
+ BasicBlock *ExitBlock = L->getExitBlock();
+ if (!ExitBlock) return;
+
+ BasicBlock *Preheader = L->getLoopPreheader();
+ if (!Preheader) return;
+
+ Instruction *InsertPt = ExitBlock->getFirstNonPHI();
+ BasicBlock::iterator I = Preheader->getTerminator();
+ while (I != Preheader->begin()) {
+ --I;
+ // New instructions were inserted at the end of the preheader.
+ if (isa<PHINode>(I))
+ break;
+
+ // Don't move instructions which might have side effects, since the side
+ // effects need to complete before instructions inside the loop. Also don't
+ // move instructions which might read memory, since the loop may modify
+ // memory. Note that it's okay if the instruction might have undefined
+ // behavior: LoopSimplify guarantees that the preheader dominates the exit
+ // block.
+ if (I->mayHaveSideEffects() || I->mayReadFromMemory())
+ continue;
+
+ // Skip debug info intrinsics.
+ if (isa<DbgInfoIntrinsic>(I))
+ continue;
+
+ // Don't sink static AllocaInsts out of the entry block, which would
+ // turn them into dynamic allocas!
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
+ if (AI->isStaticAlloca())
+ continue;
+
+ // Determine if there is a use in or before the loop (direct or
+ // otherwise).
+ bool UsedInLoop = false;
+ for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
+ UI != UE; ++UI) {
+ User *U = *UI;
+ BasicBlock *UseBB = cast<Instruction>(U)->getParent();
+ if (PHINode *P = dyn_cast<PHINode>(U)) {
+ unsigned i =
+ PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
+ UseBB = P->getIncomingBlock(i);
+ }
+ if (UseBB == Preheader || L->contains(UseBB)) {
+ UsedInLoop = true;
+ break;
+ }
+ }
+
+ // If there is, the def must remain in the preheader.
+ if (UsedInLoop)
+ continue;
+
+ // Otherwise, sink it to the exit block.
+ Instruction *ToMove = I;
+ bool Done = false;
+
+ if (I != Preheader->begin()) {
+ // Skip debug info intrinsics.
+ do {
+ --I;
+ } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
+
+ if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
+ Done = true;
+ } else {
+ Done = true;
+ }
+
+ ToMove->moveBefore(InsertPt);
+ if (Done) break;
+ InsertPt = ToMove;
+ }
+}
+
+//===----------------------------------------------------------------------===//
+// IndVarSimplify driver. Manage several subpasses of IV simplification.
+//===----------------------------------------------------------------------===//
+
+bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
+ // If LoopSimplify form is not available, stay out of trouble. Some notes:
+ // - LSR currently only supports LoopSimplify-form loops. Indvars'
+ // canonicalization can be a pessimization without LSR to "clean up"
+ // afterwards.
+ // - We depend on having a preheader; in particular,
+ // Loop::getCanonicalInductionVariable only supports loops with preheaders,
+ // and we're in trouble if we can't find the induction variable even when
+ // we've manually inserted one.
+ if (!L->isLoopSimplifyForm())
+ return false;
+
+ if (!DisableIVRewrite)
+ IU = &getAnalysis<IVUsers>();
+ LI = &getAnalysis<LoopInfo>();
+ SE = &getAnalysis<ScalarEvolution>();
+ DT = &getAnalysis<DominatorTree>();
+ TD = getAnalysisIfAvailable<TargetData>();
+
+ DeadInsts.clear();
+ Changed = false;
+
+ // If there are any floating-point recurrences, attempt to
+ // transform them to use integer recurrences.
+ RewriteNonIntegerIVs(L);
+
+ const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
+
+ // Create a rewriter object which we'll use to transform the code with.
+ SCEVExpander Rewriter(*SE, "indvars");
+
+ // Eliminate redundant IV users.
//
- // We give preference to sitofp over uitofp because it is faster on most
- // platforms.
- if (WeakPH) {
- Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
- PN->getParent()->getFirstNonPHI());
- PN->replaceAllUsesWith(Conv);
- RecursivelyDeleteTriviallyDeadInstructions(PN);
+ // Simplification works best when run before other consumers of SCEV. We
+ // attempt to avoid evaluating SCEVs for sign/zero extend operations until
+ // other expressions involving loop IVs have been evaluated. This helps SCEV
+ // set no-wrap flags before normalizing sign/zero extension.
+ if (DisableIVRewrite) {
+ Rewriter.disableCanonicalMode();
+ SimplifyIVUsersNoRewrite(L, Rewriter);
}
- // Add a new IVUsers entry for the newly-created integer PHI.
- IU->AddUsersIfInteresting(NewPHI);
+ // Check to see if this loop has a computable loop-invariant execution count.
+ // If so, this means that we can compute the final value of any expressions
+ // that are recurrent in the loop, and substitute the exit values from the
+ // loop into any instructions outside of the loop that use the final values of
+ // the current expressions.
+ //
+ if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
+ RewriteLoopExitValues(L, Rewriter);
+
+ // Eliminate redundant IV users.
+ if (!DisableIVRewrite)
+ SimplifyIVUsers(Rewriter);
+
+ // Eliminate redundant IV cycles.
+ if (DisableIVRewrite)
+ SimplifyCongruentIVs(L);
+
+ // Compute the type of the largest recurrence expression, and decide whether
+ // a canonical induction variable should be inserted.
+ Type *LargestType = 0;
+ bool NeedCannIV = false;
+ bool ReuseIVForExit = DisableIVRewrite && !ForceLFTR;
+ bool ExpandBECount = canExpandBackedgeTakenCount(L, SE);
+ if (ExpandBECount && !ReuseIVForExit) {
+ // If we have a known trip count and a single exit block, we'll be
+ // rewriting the loop exit test condition below, which requires a
+ // canonical induction variable.
+ NeedCannIV = true;
+ Type *Ty = BackedgeTakenCount->getType();
+ if (DisableIVRewrite) {
+ // In this mode, SimplifyIVUsers may have already widened the IV used by
+ // the backedge test and inserted a Trunc on the compare's operand. Get
+ // the wider type to avoid creating a redundant narrow IV only used by the
+ // loop test.
+ LargestType = getBackedgeIVType(L);
+ }
+ if (!LargestType ||
+ SE->getTypeSizeInBits(Ty) >
+ SE->getTypeSizeInBits(LargestType))
+ LargestType = SE->getEffectiveSCEVType(Ty);
+ }
+ if (!DisableIVRewrite) {
+ for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
+ NeedCannIV = true;
+ Type *Ty =
+ SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType());
+ if (!LargestType ||
+ SE->getTypeSizeInBits(Ty) >
+ SE->getTypeSizeInBits(LargestType))
+ LargestType = Ty;
+ }
+ }
+
+ // Now that we know the largest of the induction variable expressions
+ // in this loop, insert a canonical induction variable of the largest size.
+ PHINode *IndVar = 0;
+ if (NeedCannIV) {
+ // Check to see if the loop already has any canonical-looking induction
+ // variables. If any are present and wider than the planned canonical
+ // induction variable, temporarily remove them, so that the Rewriter
+ // doesn't attempt to reuse them.
+ SmallVector<PHINode *, 2> OldCannIVs;
+ while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) {
+ if (SE->getTypeSizeInBits(OldCannIV->getType()) >
+ SE->getTypeSizeInBits(LargestType))
+ OldCannIV->removeFromParent();
+ else
+ break;
+ OldCannIVs.push_back(OldCannIV);
+ }
+
+ IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType);
+
+ ++NumInserted;
+ Changed = true;
+ DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n');
+
+ // Now that the official induction variable is established, reinsert
+ // any old canonical-looking variables after it so that the IR remains
+ // consistent. They will be deleted as part of the dead-PHI deletion at
+ // the end of the pass.
+ while (!OldCannIVs.empty()) {
+ PHINode *OldCannIV = OldCannIVs.pop_back_val();
+ OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI());
+ }
+ }
+ else if (ExpandBECount && ReuseIVForExit && needsLFTR(L, DT)) {
+ IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT, TD);
+ }
+ // If we have a trip count expression, rewrite the loop's exit condition
+ // using it. We can currently only handle loops with a single exit.
+ Value *NewICmp = 0;
+ if (ExpandBECount && IndVar) {
+ // Check preconditions for proper SCEVExpander operation. SCEV does not
+ // express SCEVExpander's dependencies, such as LoopSimplify. Instead any
+ // pass that uses the SCEVExpander must do it. This does not work well for
+ // loop passes because SCEVExpander makes assumptions about all loops, while
+ // LoopPassManager only forces the current loop to be simplified.
+ //
+ // FIXME: SCEV expansion has no way to bail out, so the caller must
+ // explicitly check any assumptions made by SCEV. Brittle.
+ const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(BackedgeTakenCount);
+ if (!AR || AR->getLoop()->getLoopPreheader())
+ NewICmp =
+ LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, Rewriter);
+ }
+ // Rewrite IV-derived expressions.
+ if (!DisableIVRewrite)
+ RewriteIVExpressions(L, Rewriter);
+
+ // Clear the rewriter cache, because values that are in the rewriter's cache
+ // can be deleted in the loop below, causing the AssertingVH in the cache to
+ // trigger.
+ Rewriter.clear();
+
+ // Now that we're done iterating through lists, clean up any instructions
+ // which are now dead.
+ while (!DeadInsts.empty())
+ if (Instruction *Inst =
+ dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
+ RecursivelyDeleteTriviallyDeadInstructions(Inst);
+
+ // The Rewriter may not be used from this point on.
+
+ // Loop-invariant instructions in the preheader that aren't used in the
+ // loop may be sunk below the loop to reduce register pressure.
+ SinkUnusedInvariants(L);
+
+ // For completeness, inform IVUsers of the IV use in the newly-created
+ // loop exit test instruction.
+ if (IU && NewICmp) {
+ ICmpInst *NewICmpInst = dyn_cast<ICmpInst>(NewICmp);
+ if (NewICmpInst)
+ IU->AddUsersIfInteresting(cast<Instruction>(NewICmpInst->getOperand(0)));
+ }
+ // Clean up dead instructions.
+ Changed |= DeleteDeadPHIs(L->getHeader());
+ // Check a post-condition.
+ assert(L->isLCSSAForm(*DT) &&
+ "Indvars did not leave the loop in lcssa form!");
+
+ // Verify that LFTR, and any other change have not interfered with SCEV's
+ // ability to compute trip count.
+#ifndef NDEBUG
+ if (DisableIVRewrite && !isa<SCEVCouldNotCompute>(BackedgeTakenCount)) {
+ SE->forgetLoop(L);
+ const SCEV *NewBECount = SE->getBackedgeTakenCount(L);
+ if (SE->getTypeSizeInBits(BackedgeTakenCount->getType()) <
+ SE->getTypeSizeInBits(NewBECount->getType()))
+ NewBECount = SE->getTruncateOrNoop(NewBECount,
+ BackedgeTakenCount->getType());
+ else
+ BackedgeTakenCount = SE->getTruncateOrNoop(BackedgeTakenCount,
+ NewBECount->getType());
+ assert(BackedgeTakenCount == NewBECount && "indvars must preserve SCEV");
+ }
+#endif
+
+ return Changed;
}
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