// which starts at zero and steps by one.
// 2. The canonical induction variable is guaranteed to be the first PHI node
// in the loop header block.
-// 3. Any pointer arithmetic recurrences are raised to use array subscripts.
+// 3. The canonical induction variable is guaranteed to be in a wide enough
+// type so that IV expressions need not be (directly) zero-extended or
+// sign-extended.
+// 4. Any pointer arithmetic recurrences are raised to use array subscripts.
//
// If the trip count of a loop is computable, this pass also makes the following
// changes:
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/LLVMContext.h"
#include "llvm/Type.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/IVUsers.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
-#include "llvm/Support/CommandLine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
STATISTIC(NumLFTR , "Number of loop exit tests replaced");
namespace {
- class VISIBILITY_HIDDEN IndVarSimplify : public LoopPass {
+ class IndVarSimplify : public LoopPass {
IVUsers *IU;
LoopInfo *LI;
ScalarEvolution *SE;
+ DominatorTree *DT;
bool Changed;
public:
- static char ID; // Pass identification, replacement for typeid
- IndVarSimplify() : LoopPass(&ID) {}
-
- virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<DominatorTree>();
- AU.addRequired<ScalarEvolution>();
- AU.addRequiredID(LCSSAID);
- AU.addRequiredID(LoopSimplifyID);
- AU.addRequired<LoopInfo>();
- AU.addRequired<IVUsers>();
- AU.addPreserved<ScalarEvolution>();
- AU.addPreservedID(LoopSimplifyID);
- AU.addPreserved<IVUsers>();
- AU.addPreservedID(LCSSAID);
- AU.setPreservesCFG();
- }
+ static char ID; // Pass identification, replacement for typeid
+ IndVarSimplify() : LoopPass(&ID) {}
+
+ virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<DominatorTree>();
+ AU.addRequired<LoopInfo>();
+ AU.addRequired<ScalarEvolution>();
+ AU.addRequiredID(LoopSimplifyID);
+ AU.addRequiredID(LCSSAID);
+ AU.addRequired<IVUsers>();
+ AU.addPreserved<ScalarEvolution>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreservedID(LCSSAID);
+ AU.addPreserved<IVUsers>();
+ AU.setPreservesCFG();
+ }
private:
+ void EliminateIVComparisons();
+ void EliminateIVRemainders();
void RewriteNonIntegerIVs(Loop *L);
- ICmpInst *LinearFunctionTestReplace(Loop *L, SCEVHandle BackedgeTakenCount,
- Value *IndVar,
+ ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
+ PHINode *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter);
- void RewriteLoopExitValues(Loop *L, const SCEV *BackedgeTakenCount);
+ void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
- void RewriteIVExpressions(Loop *L, const Type *LargestType,
- SCEVExpander &Rewriter);
+ void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
- void SinkUnusedInvariants(Loop *L, SCEVExpander &Rewriter);
-
- void FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter);
+ void SinkUnusedInvariants(Loop *L);
void HandleFloatingPointIV(Loop *L, PHINode *PH);
};
}
char IndVarSimplify::ID = 0;
-static RegisterPass<IndVarSimplify>
-X("indvars", "Canonicalize Induction Variables");
+INITIALIZE_PASS(IndVarSimplify, "indvars",
+ "Canonicalize Induction Variables", false, false);
Pass *llvm::createIndVarSimplifyPass() {
return new IndVarSimplify();
/// 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,
- SCEVHandle BackedgeTakenCount,
- Value *IndVar,
+ const SCEV *BackedgeTakenCount,
+ PHINode *IndVar,
BasicBlock *ExitingBlock,
BranchInst *BI,
SCEVExpander &Rewriter) {
+ // Special case: If the backedge-taken count is a UDiv, it's very likely a
+ // UDiv that ScalarEvolution produced in order 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>(BackedgeTakenCount)) {
+ ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!OrigCond) return 0;
+ const SCEV *R = SE->getSCEV(OrigCond->getOperand(1));
+ R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1));
+ if (R != BackedgeTakenCount) {
+ const SCEV *L = SE->getSCEV(OrigCond->getOperand(0));
+ L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1));
+ if (L != BackedgeTakenCount)
+ return 0;
+ }
+ }
+
// 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;
- SCEVHandle RHS = BackedgeTakenCount;
+ 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.
- SCEVHandle Zero = SE->getIntegerSCEV(0, BackedgeTakenCount->getType());
- SCEVHandle N =
+ const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0);
+ const SCEV *N =
SE->getAddExpr(BackedgeTakenCount,
- SE->getIntegerSCEV(1, BackedgeTakenCount->getType()));
+ SE->getConstant(BackedgeTakenCount->getType(), 1));
if ((isa<SCEVConstant>(N) && !N->isZero()) ||
- SE->isLoopGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
+ SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) {
// No overflow. Cast the sum.
RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType());
} else {
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
IndVar->getType());
RHS = SE->getAddExpr(RHS,
- SE->getIntegerSCEV(1, IndVar->getType()));
+ SE->getConstant(IndVar->getType(), 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 = L->getCanonicalInductionVariableIncrement();
+ CmpIndVar = IndVar->getIncomingValueForBlock(ExitingBlock);
} else {
// We have to use the preincremented value...
RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
CmpIndVar = IndVar;
}
- // Expand the code for the iteration count into the preheader of the loop.
- BasicBlock *Preheader = L->getLoopPreheader();
- Value *ExitCnt = Rewriter.expandCodeFor(RHS, CmpIndVar->getType(),
- Preheader->getTerminator());
+ // 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;
else
Opcode = ICmpInst::ICMP_EQ;
- DOUT << "INDVARS: Rewriting loop exit condition to:\n"
- << " LHS:" << *CmpIndVar // includes a newline
- << " op:\t"
- << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
- << " RHS:\t" << *RHS << "\n";
+ DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
+ << " LHS:" << *CmpIndVar << '\n'
+ << " op:\t"
+ << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
+ << " RHS:\t" << *RHS << "\n");
- ICmpInst *Cond = new ICmpInst(Opcode, CmpIndVar, ExitCnt, "exitcond", BI);
+ ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
- Instruction *OrigCond = cast<Instruction>(BI->getCondition());
+ 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
/// 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,
- const SCEV *BackedgeTakenCount) {
+ SCEVExpander &Rewriter) {
// Verify the input to the pass in already in LCSSA form.
- assert(L->isLCSSAForm());
-
- BasicBlock *Preheader = L->getLoopPreheader();
-
- // Scan all of the instructions in the loop, looking at those that have
- // extra-loop users and which are recurrences.
- SCEVExpander Rewriter(*SE);
+ assert(L->isLCSSAForm(*DT));
- // We insert the code into the preheader of the loop if the loop contains
- // multiple exit blocks, or in the exit block if there is exactly one.
- BasicBlock *BlockToInsertInto;
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getUniqueExitBlocks(ExitBlocks);
- if (ExitBlocks.size() == 1)
- BlockToInsertInto = ExitBlocks[0];
- else
- BlockToInsertInto = Preheader;
- BasicBlock::iterator InsertPt = BlockToInsertInto->getFirstNonPHI();
-
- std::map<Instruction*, Value*> ExitValues;
// 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
// 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
+
+ // SCEV only supports integer expressions for now.
+ if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy())
+ continue;
+
+ // 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);
// 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) ||
- // SCEV only supports integer expressions for now.
- (!isa<IntegerType>(InVal->getType()) &&
- !isa<PointerType>(InVal->getType())))
+ if (!isa<Instruction>(InVal))
continue;
// If this pred is for a subloop, not L itself, skip it.
// Check that InVal is defined in the loop.
Instruction *Inst = cast<Instruction>(InVal);
- if (!L->contains(Inst->getParent()))
+ if (!L->contains(Inst))
continue;
// 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.
- SCEVHandle SH = SE->getSCEV(Inst);
- SCEVHandle ExitValue = SE->getSCEVAtScope(SH, L->getParentLoop());
- if (isa<SCEVCouldNotCompute>(ExitValue) ||
- !ExitValue->isLoopInvariant(L))
+ const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
+ if (!ExitValue->isLoopInvariant(L))
continue;
Changed = true;
++NumReplaced;
- // See if we already computed the exit value for the instruction, if so,
- // just reuse it.
- Value *&ExitVal = ExitValues[Inst];
- if (!ExitVal)
- ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), InsertPt);
+ Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
- DOUT << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal
- << " LoopVal = " << *Inst << "\n";
+ DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
+ << " LoopVal = " << *Inst << "\n");
PN->setIncomingValue(i, ExitVal);
// If this instruction is dead now, delete it.
RecursivelyDeleteTriviallyDeadInstructions(Inst);
- // See if this is a single-entry LCSSA PHI node. If so, we can (and
- // have to) remove
- // the PHI entirely. This is safe, because the NewVal won't be variant
- // in the loop, so we don't need an LCSSA phi node anymore.
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);
- Rewriter.clear();
RecursivelyDeleteTriviallyDeadInstructions(PN);
- break;
}
}
+ 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();
+ }
}
}
+
+ // The insertion point instruction may have been deleted; clear it out
+ // so that the rewriter doesn't trip over it later.
+ Rewriter.clearInsertPoint();
}
void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
// may not have been able to compute a trip count. Now that we've done some
// re-writing, the trip count may be computable.
if (Changed)
- SE->forgetLoopBackedgeTakenCount(L);
+ SE->forgetLoop(L);
+}
+
+void IndVarSimplify::EliminateIVComparisons() {
+ SmallVector<WeakVH, 16> DeadInsts;
+
+ // 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;
+
+ bool Swapped = UI.getOperandValToReplace() == ICmp->getOperand(1);
+ ICmpInst::Predicate Pred = ICmp->getPredicate();
+ if (Swapped) Pred = ICmpInst::getSwappedPredicate(Pred);
+
+ // Get the SCEVs for the ICmp operands.
+ const SCEV *S = IU->getReplacementExpr(UI);
+ const SCEV *X = SE->getSCEV(ICmp->getOperand(!Swapped));
+
+ // 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
+ continue;
+
+ DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
+ DeadInsts.push_back(ICmp);
+ }
+
+ // 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);
+}
+
+void IndVarSimplify::EliminateIVRemainders() {
+ SmallVector<WeakVH, 16> DeadInsts;
+
+ // Look for SRem and URem users.
+ for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
+ IVStrideUse &UI = *I;
+ BinaryOperator *Rem = dyn_cast<BinaryOperator>(UI.getUser());
+ if (!Rem) continue;
+
+ bool isSigned = Rem->getOpcode() == Instruction::SRem;
+ if (!isSigned && Rem->getOpcode() != Instruction::URem)
+ continue;
+
+ // We're only interested in the case where we know something about
+ // the numerator.
+ if (UI.getOperandValToReplace() != Rem->getOperand(0))
+ continue;
+
+ // 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)) &&
+ SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+ LessOne, X)) {
+ 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);
+ } else
+ continue;
+ }
+
+ // Inform IVUsers about the new users.
+ if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
+ IU->AddUsersIfInteresting(I);
+
+ DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
+ DeadInsts.push_back(Rem);
+ }
+
+ // 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);
}
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;
+
IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
+ DT = &getAnalysis<DominatorTree>();
Changed = false;
// If there are any floating-point recurrences, attempt to
// transform them to use integer recurrences.
RewriteNonIntegerIVs(L);
- BasicBlock *Header = L->getHeader();
BasicBlock *ExitingBlock = L->getExitingBlock(); // may be null
- SCEVHandle BackedgeTakenCount = SE->getBackedgeTakenCount(L);
+ const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
+
+ // Create a rewriter object which we'll use to transform the code with.
+ SCEVExpander Rewriter(*SE);
// 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
// the current expressions.
//
if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount))
- RewriteLoopExitValues(L, BackedgeTakenCount);
+ RewriteLoopExitValues(L, Rewriter);
+
+ // Simplify ICmp IV users.
+ EliminateIVComparisons();
+
+ // Simplify SRem and URem IV users.
+ EliminateIVRemainders();
// Compute the type of the largest recurrence expression, and decide whether
// a canonical induction variable should be inserted.
if (ExitingBlock)
NeedCannIV = true;
}
- for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
- SCEVHandle Stride = IU->StrideOrder[i];
- const Type *Ty = SE->getEffectiveSCEVType(Stride->getType());
+ 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;
-
- std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
- IU->IVUsesByStride.find(IU->StrideOrder[i]);
- assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
-
- if (!SI->second->Users.empty())
- NeedCannIV = true;
+ NeedCannIV = true;
}
- // Create a rewriter object which we'll use to transform the code with.
- SCEVExpander Rewriter(*SE);
-
- // Now that we know the largest of of the induction variable expressions
+ // 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;
+ PHINode *IndVar = 0;
if (NeedCannIV) {
- IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType);
+ // 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;
- DOUT << "INDVARS: New CanIV: " << *IndVar;
+ 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());
+ }
}
// 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) && ExitingBlock) {
+ if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
+ !BackedgeTakenCount->isZero() &&
+ ExitingBlock) {
assert(NeedCannIV &&
"LinearFunctionTestReplace requires a canonical induction variable");
// Can't rewrite non-branch yet.
ExitingBlock, BI, Rewriter);
}
- Rewriter.setInsertionPoint(Header->getFirstNonPHI());
+ // Rewrite IV-derived expressions. Clears the rewriter cache.
+ RewriteIVExpressions(L, Rewriter);
- // Rewrite IV-derived expressions.
- RewriteIVExpressions(L, LargestType, Rewriter);
+ // 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, Rewriter);
+ SinkUnusedInvariants(L);
- // Reorder instructions to avoid use-before-def conditions.
- FixUsesBeforeDefs(L, Rewriter);
-
- Rewriter.clear();
// 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.
- DeleteDeadPHIs(L->getHeader());
+ Changed |= DeleteDeadPHIs(L->getHeader());
// Check a post-condition.
- assert(L->isLCSSAForm() && "Indvars did not leave the loop in lcssa form!");
+ assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
return Changed;
}
-void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType,
- SCEVExpander &Rewriter) {
+// FIXME: It is an extremely bad idea to indvar substitute anything more
+// complex than affine induction variables. Doing so will put expensive
+// polynomial evaluations inside of the loop, and the str reduction pass
+// 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) {
+ // Loop-invariant values are safe.
+ if (S->isLoopInvariant(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 SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S))
+ return AR->isAffine();
+
+ // An add is safe it all its operands are safe.
+ 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;
+ return true;
+ }
+
+ // A cast is safe if its operand is.
+ if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S))
+ return isSafe(C->getOperand(), L);
+
+ // 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);
+
+ // SCEVUnknown is always safe.
+ if (isa<SCEVUnknown>(S))
+ return true;
+
+ // Nothing else is safe.
+ return false;
+}
+
+void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
SmallVector<WeakVH, 16> DeadInsts;
// Rewrite all induction variable expressions in terms of the canonical
// add the offsets to the primary induction variable and cast, avoiding
// the need for the code evaluation methods to insert induction variables
// of different sizes.
- for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) {
- SCEVHandle Stride = IU->StrideOrder[i];
-
- std::map<SCEVHandle, IVUsersOfOneStride *>::iterator SI =
- IU->IVUsesByStride.find(IU->StrideOrder[i]);
- assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!");
- ilist<IVStrideUse> &List = SI->second->Users;
- for (ilist<IVStrideUse>::iterator UI = List.begin(),
- E = List.end(); UI != E; ++UI) {
- SCEVHandle Offset = UI->getOffset();
- Value *Op = UI->getOperandValToReplace();
- Instruction *User = UI->getUser();
- bool isSigned = UI->isSigned();
-
- // Compute the final addrec to expand into code.
- SCEVHandle AR = IU->getReplacementExpr(*UI);
-
- // FIXME: It is an extremely bad idea to indvar substitute anything more
- // complex than affine induction variables. Doing so will put expensive
- // polynomial evaluations inside of the loop, and the str reduction pass
- // 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 (!Stride->isLoopInvariant(L) &&
- !isa<SCEVConstant>(AR) &&
- L->contains(User->getParent()))
- continue;
+ for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) {
+ Value *Op = UI->getOperandValToReplace();
+ const Type *UseTy = Op->getType();
+ Instruction *User = UI->getUser();
+
+ // Compute the final addrec to expand into code.
+ const SCEV *AR = IU->getReplacementExpr(*UI);
+
+ // 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))
+ AR = ExitVal;
+ }
- Value *NewVal = 0;
- if (AR->isLoopInvariant(L)) {
- BasicBlock::iterator I = Rewriter.getInsertionPoint();
- // Expand loop-invariant values in the loop preheader. They will
- // be sunk to the exit block later, if possible.
- NewVal =
- Rewriter.expandCodeFor(AR, LargestType,
- L->getLoopPreheader()->getTerminator());
- Rewriter.setInsertionPoint(I);
- ++NumReplaced;
- } else {
- const Type *IVTy = Offset->getType();
- const Type *UseTy = Op->getType();
-
- // Promote the Offset and Stride up to the canonical induction
- // variable's bit width.
- SCEVHandle PromotedOffset = Offset;
- SCEVHandle PromotedStride = Stride;
- if (SE->getTypeSizeInBits(IVTy) != SE->getTypeSizeInBits(LargestType)) {
- // It doesn't matter for correctness whether zero or sign extension
- // is used here, since the value is truncated away below, but if the
- // value is signed, sign extension is more likely to be folded.
- if (isSigned) {
- PromotedOffset = SE->getSignExtendExpr(PromotedOffset, LargestType);
- PromotedStride = SE->getSignExtendExpr(PromotedStride, LargestType);
- } else {
- PromotedOffset = SE->getZeroExtendExpr(PromotedOffset, LargestType);
- // If the stride is obviously negative, use sign extension to
- // produce things like x-1 instead of x+255.
- if (isa<SCEVConstant>(PromotedStride) &&
- cast<SCEVConstant>(PromotedStride)
- ->getValue()->getValue().isNegative())
- PromotedStride = SE->getSignExtendExpr(PromotedStride,
- LargestType);
- else
- PromotedStride = SE->getZeroExtendExpr(PromotedStride,
- LargestType);
- }
- }
+ // FIXME: It is an extremely bad idea to indvar substitute anything more
+ // complex than affine induction variables. Doing so will put expensive
+ // polynomial evaluations inside of the loop, and the str reduction pass
+ // 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))
+ continue;
- // Create the SCEV representing the offset from the canonical
- // induction variable, still in the canonical induction variable's
- // type, so that all expanded arithmetic is done in the same type.
- SCEVHandle NewAR = SE->getAddRecExpr(SE->getIntegerSCEV(0, LargestType),
- PromotedStride, L);
- // Add the PromotedOffset as a separate step, because it may not be
- // loop-invariant.
- NewAR = SE->getAddExpr(NewAR, PromotedOffset);
-
- // Expand the addrec into instructions.
- Value *V = Rewriter.expandCodeFor(NewAR);
-
- // Insert an explicit cast if necessary to truncate the value
- // down to the original stride type. This is done outside of
- // SCEVExpander because in SCEV expressions, a truncate of an
- // addrec is always folded.
- if (LargestType != IVTy) {
- if (SE->getTypeSizeInBits(IVTy) != SE->getTypeSizeInBits(LargestType))
- NewAR = SE->getTruncateExpr(NewAR, IVTy);
- if (Rewriter.isInsertedExpression(NewAR))
- V = Rewriter.expandCodeFor(NewAR);
- else {
- V = Rewriter.InsertCastOfTo(CastInst::getCastOpcode(V, false,
- IVTy, false),
- V, IVTy);
- assert(!isa<SExtInst>(V) && !isa<ZExtInst>(V) &&
- "LargestType wasn't actually the largest type!");
- // Force the rewriter to use this trunc whenever this addrec
- // appears so that it doesn't insert new phi nodes or
- // arithmetic in a different type.
- Rewriter.addInsertedValue(V, NewAR);
- }
+ // Determine the insertion point for this user. By default, insert
+ // immediately before the user. The SCEVExpander class will automatically
+ // 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();
}
- DOUT << "INDVARS: Made offset-and-trunc IV for offset "
- << *IVTy << " " << *Offset << ": ";
- DEBUG(WriteAsOperand(*DOUT, V, false));
- DOUT << "\n";
-
- // Now expand it into actual Instructions and patch it into place.
- NewVal = Rewriter.expandCodeFor(AR, UseTy);
- }
+ // Now expand it into actual Instructions and patch it into place.
+ Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt);
+
+ // 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
+ // ability to walk use lists and drop dangling pointers when a value is
+ // deleted.
+ SE->forgetValue(User);
+
+ // Patch the new value into place.
+ if (Op->hasName())
+ NewVal->takeName(Op);
+ User->replaceUsesOfWith(Op, NewVal);
+ UI->setOperandValToReplace(NewVal);
+ DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n'
+ << " into = " << *NewVal << "\n");
+ ++NumRemoved;
+ Changed = true;
- // Patch the new value into place.
- if (Op->hasName())
- NewVal->takeName(Op);
- User->replaceUsesOfWith(Op, NewVal);
- UI->setOperandValToReplace(NewVal);
- DOUT << "INDVARS: Rewrote IV '" << *AR << "' " << *Op
- << " into = " << *NewVal << "\n";
- ++NumRemoved;
- Changed = true;
-
- // The old value may be dead now.
- DeadInsts.push_back(Op);
- }
+ // 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()) {
- Instruction *Inst = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val());
- if (Inst)
+ while (!DeadInsts.empty())
+ if (Instruction *Inst =
+ dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
RecursivelyDeleteTriviallyDeadInstructions(Inst);
- }
}
/// 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, SCEVExpander &Rewriter) {
+void IndVarSimplify::SinkUnusedInvariants(Loop *L) {
BasicBlock *ExitBlock = L->getExitBlock();
if (!ExitBlock) return;
- Instruction *NonPHI = ExitBlock->getFirstNonPHI();
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. Only
- // consider those new instructions.
- if (!Rewriter.isInsertedInstruction(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) {
- BasicBlock *UseBB = cast<Instruction>(UI)->getParent();
- if (PHINode *P = dyn_cast<PHINode>(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);
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())
- --I;
- else
- Done = true;
- ToMove->moveBefore(NonPHI);
- if (Done)
- break;
- }
-}
-/// Re-schedule the inserted instructions to put defs before uses. This
-/// fixes problems that arrise when SCEV expressions contain loop-variant
-/// values unrelated to the induction variable which are defined inside the
-/// loop. FIXME: It would be better to insert instructions in the right
-/// place so that this step isn't needed.
-void IndVarSimplify::FixUsesBeforeDefs(Loop *L, SCEVExpander &Rewriter) {
- // Visit all the blocks in the loop in pre-order dom-tree dfs order.
- DominatorTree *DT = &getAnalysis<DominatorTree>();
- std::map<Instruction *, unsigned> NumPredsLeft;
- SmallVector<DomTreeNode *, 16> Worklist;
- Worklist.push_back(DT->getNode(L->getHeader()));
- do {
- DomTreeNode *Node = Worklist.pop_back_val();
- for (DomTreeNode::iterator I = Node->begin(), E = Node->end(); I != E; ++I)
- if (L->contains((*I)->getBlock()))
- Worklist.push_back(*I);
- BasicBlock *BB = Node->getBlock();
- // Visit all the instructions in the block top down.
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
- // Count the number of operands that aren't properly dominating.
- unsigned NumPreds = 0;
- if (Rewriter.isInsertedInstruction(I) && !isa<PHINode>(I))
- for (User::op_iterator OI = I->op_begin(), OE = I->op_end();
- OI != OE; ++OI)
- if (Instruction *Inst = dyn_cast<Instruction>(OI))
- if (L->contains(Inst->getParent()) && !NumPredsLeft.count(Inst))
- ++NumPreds;
- NumPredsLeft[I] = NumPreds;
- // Notify uses of the position of this instruction, and move the
- // users (and their dependents, recursively) into place after this
- // instruction if it is their last outstanding operand.
- for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
- UI != UE; ++UI) {
- Instruction *Inst = cast<Instruction>(UI);
- std::map<Instruction *, unsigned>::iterator Z = NumPredsLeft.find(Inst);
- if (Z != NumPredsLeft.end() && Z->second != 0 && --Z->second == 0) {
- SmallVector<Instruction *, 4> UseWorkList;
- UseWorkList.push_back(Inst);
- BasicBlock::iterator InsertPt = I;
- if (InvokeInst *II = dyn_cast<InvokeInst>(InsertPt))
- InsertPt = II->getNormalDest()->begin();
- else
- ++InsertPt;
- while (isa<PHINode>(InsertPt)) ++InsertPt;
- do {
- Instruction *Use = UseWorkList.pop_back_val();
- Use->moveBefore(InsertPt);
- NumPredsLeft.erase(Use);
- for (Value::use_iterator IUI = Use->use_begin(),
- IUE = Use->use_end(); IUI != IUE; ++IUI) {
- Instruction *IUIInst = cast<Instruction>(IUI);
- if (L->contains(IUIInst->getParent()) &&
- Rewriter.isInsertedInstruction(IUIInst) &&
- !isa<PHINode>(IUIInst))
- UseWorkList.push_back(IUIInst);
- }
- } while (!UseWorkList.empty());
- }
- }
- }
- } while (!Worklist.empty());
-}
-
-/// Return true if it is OK to use SIToFPInst for an inducation variable
-/// with given inital and exit values.
-static bool useSIToFPInst(ConstantFP &InitV, ConstantFP &ExitV,
- uint64_t intIV, uint64_t intEV) {
+ if (I != Preheader->begin()) {
+ // Skip debug info intrinsics.
+ do {
+ --I;
+ } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin());
- if (InitV.getValueAPF().isNegative() || ExitV.getValueAPF().isNegative())
- return true;
-
- // If the iteration range can be handled by SIToFPInst then use it.
- APInt Max = APInt::getSignedMaxValue(32);
- if (Max.getZExtValue() > static_cast<uint64_t>(abs64(intEV - intIV)))
- return true;
+ if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin())
+ Done = true;
+ } else {
+ Done = true;
+ }
- return false;
+ ToMove->moveBefore(InsertPt);
+ if (Done) break;
+ InsertPt = ToMove;
+ }
}
-/// convertToInt - Convert APF to an integer, if possible.
-static bool convertToInt(const APFloat &APF, uint64_t *intVal) {
-
+/// 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;
- if (APF.convertToInteger(intVal, 32, APF.isNegative(),
- APFloat::rmTowardZero, &isExact)
- != APFloat::opOK)
- return false;
- if (!isExact)
+ // 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;
-
}
/// HandleFloatingPointIV - If the loop has floating induction variable
/// for(int i = 0; i < 10000; ++i)
/// bar((double)i);
///
-void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PH) {
-
- unsigned IncomingEdge = L->contains(PH->getIncomingBlock(0));
+void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) {
+ unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0));
unsigned BackEdge = IncomingEdge^1;
// Check incoming value.
- ConstantFP *InitValue = dyn_cast<ConstantFP>(PH->getIncomingValue(IncomingEdge));
- if (!InitValue) return;
- uint64_t newInitValue = Type::Int32Ty->getPrimitiveSizeInBits();
- if (!convertToInt(InitValue->getValueAPF(), &newInitValue))
+ ConstantFP *InitValueVal =
+ dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge));
+
+ int64_t InitValue;
+ if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue))
return;
- // Check IV increment. Reject this PH if increement operation is not
+ // 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>(PH->getIncomingValue(BackEdge));
- if (!Incr) return;
- if (Incr->getOpcode() != Instruction::Add) return;
- ConstantFP *IncrValue = NULL;
- unsigned IncrVIndex = 1;
- if (Incr->getOperand(1) == PH)
- IncrVIndex = 0;
- IncrValue = dyn_cast<ConstantFP>(Incr->getOperand(IncrVIndex));
- if (!IncrValue) return;
- uint64_t newIncrValue = Type::Int32Ty->getPrimitiveSizeInBits();
- if (!convertToInt(IncrValue->getValueAPF(), &newIncrValue))
+ 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;
- // Check Incr uses. One user is PH and the other users is exit condition used
- // by the conditional terminator.
+ // 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++);
+ Instruction *U1 = cast<Instruction>(*IncrUse++);
if (IncrUse == Incr->use_end()) return;
- Instruction *U2 = cast<Instruction>(IncrUse++);
+ Instruction *U2 = cast<Instruction>(*IncrUse++);
if (IncrUse != Incr->use_end()) return;
- // Find exit condition.
- FCmpInst *EC = dyn_cast<FCmpInst>(U1);
- if (!EC)
- EC = dyn_cast<FCmpInst>(U2);
- if (!EC) return;
-
- if (BranchInst *BI = dyn_cast<BranchInst>(EC->getParent()->getTerminator())) {
- if (!BI->isConditional()) return;
- if (BI->getCondition() != EC) return;
- }
-
- // Find exit value. If exit value can not be represented as an interger then
- // do not handle this floating point PH.
- ConstantFP *EV = NULL;
- unsigned EVIndex = 1;
- if (EC->getOperand(1) == Incr)
- EVIndex = 0;
- EV = dyn_cast<ConstantFP>(EC->getOperand(EVIndex));
- if (!EV) return;
- uint64_t intEV = Type::Int32Ty->getPrimitiveSizeInBits();
- if (!convertToInt(EV->getValueAPF(), &intEV))
+ // 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());
+
+ // 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 (EC->getPredicate()) {
+ switch (Compare->getPredicate()) {
+ default: return; // Unknown comparison.
case CmpInst::FCMP_OEQ:
- case CmpInst::FCMP_UEQ:
- NewPred = CmpInst::ICMP_EQ;
- break;
+ 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_UGT;
- break;
+ case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break;
case CmpInst::FCMP_OGE:
- case CmpInst::FCMP_UGE:
- NewPred = CmpInst::ICMP_UGE;
- break;
+ case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break;
case CmpInst::FCMP_OLT:
- case CmpInst::FCMP_ULT:
- NewPred = CmpInst::ICMP_ULT;
- break;
+ case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break;
case CmpInst::FCMP_OLE:
- case CmpInst::FCMP_ULE:
- NewPred = CmpInst::ICMP_ULE;
- break;
- default:
- break;
+ case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break;
}
- if (NewPred == CmpInst::BAD_ICMP_PREDICATE) return;
+
+ // 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;
+
+ // If not actually striding (add x, 0.0), avoid touching the code.
+ if (IncValue == 0)
+ 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)
+ 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;
+ }
+
+ const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
// Insert new integer induction variable.
- PHINode *NewPHI = PHINode::Create(Type::Int32Ty,
- PH->getName()+".int", PH);
- NewPHI->addIncoming(ConstantInt::get(Type::Int32Ty, newInitValue),
- PH->getIncomingBlock(IncomingEdge));
-
- Value *NewAdd = BinaryOperator::CreateAdd(NewPHI,
- ConstantInt::get(Type::Int32Ty,
- newIncrValue),
- Incr->getName()+".int", Incr);
- NewPHI->addIncoming(NewAdd, PH->getIncomingBlock(BackEdge));
-
- // The back edge is edge 1 of newPHI, whatever it may have been in the
- // original PHI.
- ConstantInt *NewEV = ConstantInt::get(Type::Int32Ty, intEV);
- Value *LHS = (EVIndex == 1 ? NewPHI->getIncomingValue(1) : NewEV);
- Value *RHS = (EVIndex == 1 ? NewEV : NewPHI->getIncomingValue(1));
- ICmpInst *NewEC = new ICmpInst(NewPred, LHS, RHS, EC->getNameStart(),
- EC->getParent()->getTerminator());
-
- // In the following deltions, PH may become dead and may be deleted.
+ PHINode *NewPHI = PHINode::Create(Int32Ty, 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 = PH;
+ WeakVH WeakPH = PN;
- // Delete old, floating point, exit comparision instruction.
- NewEC->takeName(EC);
- EC->replaceAllUsesWith(NewEC);
- RecursivelyDeleteTriviallyDeadInstructions(EC);
+ // Delete the old floating point exit comparison. The branch starts using the
+ // new comparison.
+ NewCompare->takeName(Compare);
+ Compare->replaceAllUsesWith(NewCompare);
+ RecursivelyDeleteTriviallyDeadInstructions(Compare);
- // Delete old, floating point, increment instruction.
+ // Delete the old floating point increment.
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
RecursivelyDeleteTriviallyDeadInstructions(Incr);
- // Replace floating induction variable, if it isn't already deleted.
- // Give SIToFPInst preference over UIToFPInst because it is faster on
- // platforms that are widely used.
- if (WeakPH && !PH->use_empty()) {
- if (useSIToFPInst(*InitValue, *EV, newInitValue, intEV)) {
- SIToFPInst *Conv = new SIToFPInst(NewPHI, PH->getType(), "indvar.conv",
- PH->getParent()->getFirstNonPHI());
- PH->replaceAllUsesWith(Conv);
- } else {
- UIToFPInst *Conv = new UIToFPInst(NewPHI, PH->getType(), "indvar.conv",
- PH->getParent()->getFirstNonPHI());
- PH->replaceAllUsesWith(Conv);
- }
- RecursivelyDeleteTriviallyDeadInstructions(PH);
+ // 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.
projects / oota-llvm.git / blobdiff