// computations derived from them) into simpler forms suitable for subsequent
// analysis and transformation.
//
-// This transformation makes the following changes to each loop with an
-// identifiable induction variable:
-// 1. All loops are transformed to have a SINGLE canonical induction variable
-// 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. 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:
// 1. The exit condition for the loop is canonicalized to compare the
// purpose of the loop is to compute the exit value of some derived
// expression, this transformation will make the loop dead.
//
-// This transformation should be followed by strength reduction after all of the
-// desired loop transformations have been performed.
-//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "indvars"
#include "llvm/Transforms/Scalar.h"
-#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/ScalarEvolutionExpander.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
-#include "llvm/Support/CFG.h"
+#include "llvm/Analysis/ScalarEvolutionExpander.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Type.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/Target/TargetLibraryInfo.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"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/SimplifyIndVar.h"
using namespace llvm;
-STATISTIC(NumRemoved , "Number of aux indvars removed");
+#define DEBUG_TYPE "indvars"
+
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"));
+// Trip count verification can be enabled by default under NDEBUG if we
+// implement a strong expression equivalence checker in SCEV. Until then, we
+// use the verify-indvars flag, which may assert in some cases.
+static cl::opt<bool> VerifyIndvars(
+ "verify-indvars", cl::Hidden,
+ cl::desc("Verify the ScalarEvolution result after running indvars"));
+
+static cl::opt<bool> ReduceLiveIVs("liv-reduce", cl::Hidden,
+ cl::desc("Reduce live induction variables."));
namespace {
class IndVarSimplify : public LoopPass {
- IVUsers *IU;
LoopInfo *LI;
ScalarEvolution *SE;
DominatorTree *DT;
- TargetData *TD;
+ const DataLayout *DL;
+ TargetLibraryInfo *TLI;
SmallVector<WeakVH, 16> DeadInsts;
bool Changed;
public:
static char ID; // Pass identification, replacement for typeid
- IndVarSimplify() : LoopPass(ID), IU(0), LI(0), SE(0), DT(0), TD(0),
- Changed(false) {
+ IndVarSimplify() : LoopPass(ID), LI(nullptr), SE(nullptr), DT(nullptr),
+ DL(nullptr), Changed(false) {
initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
}
- virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
+ bool runOnLoop(Loop *L, LPPassManager &LPM) override;
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<DominatorTree>();
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfo>();
AU.addRequired<ScalarEvolution>();
AU.addRequiredID(LoopSimplifyID);
AU.addRequiredID(LCSSAID);
- if (!DisableIVRewrite)
- AU.addRequired<IVUsers>();
AU.addPreserved<ScalarEvolution>();
AU.addPreservedID(LoopSimplifyID);
AU.addPreservedID(LCSSAID);
- if (!DisableIVRewrite)
- AU.addPreserved<IVUsers>();
AU.setPreservesCFG();
}
private:
- virtual void releaseMemory() {
+ void releaseMemory() override {
DeadInsts.clear();
}
void HandleFloatingPointIV(Loop *L, PHINode *PH);
void RewriteNonIntegerIVs(Loop *L);
- void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
+ void SimplifyAndExtend(Loop *L, SCEVExpander &Rewriter, LPPassManager &LPM);
- 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 RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter);
- ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
- PHINode *IndVar,
- SCEVExpander &Rewriter);
+ Value *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
+ PHINode *IndVar, SCEVExpander &Rewriter);
void SinkUnusedInvariants(Loop *L);
};
char IndVarSimplify::ID = 0;
INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
"Induction Variable Simplification", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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)
// 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.
+
+ // If the GEP base pointer is a vector of pointers, abort.
+ if (!FromPtr->getType()->isPointerTy() || !ToPtr->getType()->isPointerTy())
+ return false;
+
const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr));
const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr));
if (FromBase == ToBase)
return true;
}
+/// 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 = nullptr;
+ for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
+ if (PHI->getIncomingValue(i) != Def)
+ continue;
+
+ 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;
+}
+
//===----------------------------------------------------------------------===//
// RewriteNonIntegerIVs and helpers. Prefer integer IVs.
//===----------------------------------------------------------------------===//
/// 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,
// 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 (Incr == nullptr || 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 ||
+ if (IncValueVal == nullptr || Incr->getOperand(0) != PN ||
!ConvertToSInt(IncValueVal->getValueAPF(), IncValue))
return;
// 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();
+ Value::user_iterator IncrUse = Incr->user_begin();
Instruction *U1 = cast<Instruction>(*IncrUse++);
- if (IncrUse == Incr->use_end()) return;
+ if (IncrUse == Incr->user_end()) return;
Instruction *U2 = cast<Instruction>(*IncrUse++);
- if (IncrUse != Incr->use_end()) return;
+ if (IncrUse != Incr->user_end()) return;
// 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()))
+ if (!Compare || !Compare->hasOneUse() ||
+ !isa<BranchInst>(Compare->user_back()))
return;
- BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
+ BranchInst *TheBr = cast<BranchInst>(Compare->user_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.
// transform it.
ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1));
int64_t ExitValue;
- if (ExitValueVal == 0 ||
+ if (ExitValueVal == nullptr ||
!ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue))
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)
+ // exit value.
+ if (InitValue >= ExitValue)
return;
uint32_t Range = uint32_t(ExitValue-InitValue);
- if (NewPred == CmpInst::ICMP_SLE) {
- // Normalize SLE -> SLT, check for infinite loop.
+ // Check for infinite loop, either:
+ // while (i <= Exit) or until (i > Exit)
+ if (NewPred == CmpInst::ICMP_SLE || NewPred == CmpInst::ICMP_SGT) {
if (++Range == 0) return; // Range overflows.
}
} 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)
+ // exit value.
+ if (InitValue <= ExitValue)
return;
uint32_t Range = uint32_t(InitValue-ExitValue);
- if (NewPred == CmpInst::ICMP_SGE) {
- // Normalize SGE -> SGT, check for infinite loop.
+ // Check for infinite loop, either:
+ // while (i >= Exit) or until (i < Exit)
+ if (NewPred == CmpInst::ICMP_SGE || NewPred == CmpInst::ICMP_SLT) {
if (++Range == 0) return; // Range overflows.
}
return;
}
- const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
+ IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext());
// Insert new integer induction variable.
PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN);
// new comparison.
NewCompare->takeName(Compare);
Compare->replaceAllUsesWith(NewCompare);
- RecursivelyDeleteTriviallyDeadInstructions(Compare);
+ RecursivelyDeleteTriviallyDeadInstructions(Compare, TLI);
// Delete the old floating point increment.
Incr->replaceAllUsesWith(UndefValue::get(Incr->getType()));
- RecursivelyDeleteTriviallyDeadInstructions(Incr);
+ RecursivelyDeleteTriviallyDeadInstructions(Incr, TLI);
// 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
// platforms.
if (WeakPH) {
Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv",
- PN->getParent()->getFirstNonPHI());
+ PN->getParent()->getFirstInsertionPt());
PN->replaceAllUsesWith(Conv);
- RecursivelyDeleteTriviallyDeadInstructions(PN);
+ RecursivelyDeleteTriviallyDeadInstructions(PN, TLI);
}
-
- // Add a new IVUsers entry for the newly-created integer PHI.
- if (IU)
- IU->AddUsersIfInteresting(NewPHI);
+ Changed = true;
}
void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) {
unsigned NumPreds = PN->getNumIncomingValues();
+ // We would like to be able to RAUW single-incoming value PHI nodes. We
+ // have to be certain this is safe even when this is an LCSSA PHI node.
+ // While the computed exit value is no longer varying in *this* loop, the
+ // exit block may be an exit block for an outer containing loop as well,
+ // the exit value may be varying in the outer loop, and thus it may still
+ // require an LCSSA PHI node. The safe case is when this is
+ // single-predecessor PHI node (LCSSA) and the exit block containing it is
+ // part of the enclosing loop, or this is the outer most loop of the nest.
+ // In either case the exit value could (at most) be varying in the same
+ // loop body as the phi node itself. Thus if it is in turn used outside of
+ // an enclosing loop it will only be via a separate LCSSA node.
+ bool LCSSASafePhiForRAUW =
+ NumPreds == 1 &&
+ (!L->getParentLoop() || L->getParentLoop() == LI->getLoopFor(ExitBB));
+
// Iterate over all of the PHI nodes.
BasicBlock::iterator BBI = ExitBB->begin();
while ((PN = dyn_cast<PHINode>(BBI++))) {
// 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))
+ if (!SE->isLoopInvariant(ExitValue, L) ||
+ !isSafeToExpand(ExitValue, *SE))
continue;
+ // Computing the value outside of the loop brings no benefit if :
+ // - it is definitely used inside the loop in a way which can not be
+ // optimized away.
+ // - no use outside of the loop can take advantage of hoisting the
+ // computation out of the loop
+ if (ExitValue->getSCEVType()>=scMulExpr) {
+ unsigned NumHardInternalUses = 0;
+ unsigned NumSoftExternalUses = 0;
+ unsigned NumUses = 0;
+ for (auto IB = Inst->user_begin(), IE = Inst->user_end();
+ IB != IE && NumUses <= 6; ++IB) {
+ Instruction *UseInstr = cast<Instruction>(*IB);
+ unsigned Opc = UseInstr->getOpcode();
+ NumUses++;
+ if (L->contains(UseInstr)) {
+ if (Opc == Instruction::Call || Opc == Instruction::Ret)
+ NumHardInternalUses++;
+ } else {
+ if (Opc == Instruction::PHI) {
+ // Do not count the Phi as a use. LCSSA may have inserted
+ // plenty of trivial ones.
+ NumUses--;
+ for (auto PB = UseInstr->user_begin(),
+ PE = UseInstr->user_end();
+ PB != PE && NumUses <= 6; ++PB, ++NumUses) {
+ unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode();
+ if (PhiOpc != Instruction::Call && PhiOpc != Instruction::Ret)
+ NumSoftExternalUses++;
+ }
+ continue;
+ }
+ if (Opc != Instruction::Call && Opc != Instruction::Ret)
+ NumSoftExternalUses++;
+ }
+ }
+ if (NumUses <= 6 && NumHardInternalUses && !NumSoftExternalUses)
+ continue;
+ }
+
Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst);
DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n'
PN->setIncomingValue(i, ExitVal);
- // If this instruction is dead now, delete it.
- RecursivelyDeleteTriviallyDeadInstructions(Inst);
+ // If this instruction is dead now, delete it. Don't do it now to avoid
+ // invalidating iterators.
+ if (isInstructionTriviallyDead(Inst, TLI))
+ DeadInsts.push_back(Inst);
- 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.
+ // If we determined that this PHI is safe to replace even if an LCSSA
+ // PHI, do so.
+ if (LCSSASafePhiForRAUW) {
PN->replaceAllUsesWith(ExitVal);
- RecursivelyDeleteTriviallyDeadInstructions(PN);
+ PN->eraseFromParent();
}
}
- 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.
+
+ // If we were unable to completely replace the PHI node, clone the PHI
+ // and delete the original one. This lets IVUsers and any other maps
+ // purge the original user from their records.
+ if (!LCSSASafePhiForRAUW) {
PHINode *NewPN = cast<PHINode>(PN->clone());
NewPN->takeName(PN);
NewPN->insertBefore(PN);
Rewriter.clearInsertPoint();
}
-//===----------------------------------------------------------------------===//
-// Rewrite IV users based on a canonical IV.
-// To be replaced by -disable-iv-rewrite.
-//===----------------------------------------------------------------------===//
-
-/// 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
-// 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, ScalarEvolution *SE) {
- // Loop-invariant values are safe.
- 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 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, 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, SE);
-
- // A udiv is safe if its operands are.
- if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S))
- return isSafe(UD->getLHS(), L, SE) &&
- isSafe(UD->getRHS(), L, SE);
-
- // SCEVUnknown is always safe.
- if (isa<SCEVUnknown>(S))
- return true;
-
- // Nothing else is safe.
- return false;
-}
-
-void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) {
- // Rewrite all induction variable expressions in terms of the canonical
- // induction variable.
- //
- // If there were induction variables of other sizes or offsets, manually
- // 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 (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 (SE->isLoopInvariant(ExitVal, L))
- AR = ExitVal;
- }
-
- // 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, SE))
- continue;
-
- // 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();
- }
-
- // 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
- // 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);
- if (Instruction *NewValI = dyn_cast<Instruction>(NewVal))
- NewValI->setDebugLoc(User->getDebugLoc());
- User->replaceUsesOfWith(Op, NewVal);
- UI->setOperandValToReplace(NewVal);
-
- ++NumRemoved;
- Changed = true;
-
- // The old value may be dead now.
- DeadInsts.push_back(Op);
- }
-}
-
//===----------------------------------------------------------------------===//
// IV Widening - Extend the width of an IV to cover its widest uses.
//===----------------------------------------------------------------------===//
// extend operations. This information is recorded by CollectExtend and
// provides the input to WidenIV.
struct WideIVInfo {
- const Type *WidestNativeType; // Widest integer type created [sz]ext
- bool IsSigned; // Was an sext user seen before a zext?
+ PHINode *NarrowIV;
+ Type *WidestNativeType; // Widest integer type created [sz]ext
+ bool IsSigned; // Was an sext user seen before a zext?
- WideIVInfo() : WidestNativeType(0), IsSigned(false) {}
+ WideIVInfo() : NarrowIV(nullptr), WidestNativeType(nullptr),
+ IsSigned(false) {}
};
}
-/// CollectExtend - Update information about the induction variable that is
+/// visitCast - 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) {
- const Type *Ty = Cast->getType();
+static void visitIVCast(CastInst *Cast, WideIVInfo &WI, ScalarEvolution *SE,
+ const DataLayout *DL) {
+ bool IsSigned = Cast->getOpcode() == Instruction::SExt;
+ if (!IsSigned && Cast->getOpcode() != Instruction::ZExt)
+ return;
+
+ Type *Ty = Cast->getType();
uint64_t Width = SE->getTypeSizeInBits(Ty);
- if (TD && !TD->isLegalInteger(Width))
+ if (DL && !DL->isLegalInteger(Width))
return;
if (!WI.WidestNativeType) {
}
namespace {
+
+/// 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;
+
+ NarrowIVDefUse(): NarrowDef(nullptr), NarrowUse(nullptr), WideDef(nullptr) {}
+
+ NarrowIVDefUse(Instruction *ND, Instruction *NU, Instruction *WD):
+ NarrowDef(ND), NarrowUse(NU), WideDef(WD) {}
+};
+
/// 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
class WidenIV {
// Parameters
PHINode *OrigPhi;
- const Type *WideType;
+ Type *WideType;
bool IsSigned;
// Context
SmallVectorImpl<WeakVH> &DeadInsts;
SmallPtrSet<Instruction*,16> Widened;
- SmallVector<std::pair<Use *, Instruction *>, 8> NarrowIVUsers;
+ SmallVector<NarrowIVDefUse, 8> NarrowIVUsers;
public:
- WidenIV(PHINode *PN, const WideIVInfo &WI, LoopInfo *LInfo,
+ WidenIV(const WideIVInfo &WI, LoopInfo *LInfo,
ScalarEvolution *SEv, DominatorTree *DTree,
SmallVectorImpl<WeakVH> &DI) :
- OrigPhi(PN),
+ OrigPhi(WI.NarrowIV),
WideType(WI.WidestNativeType),
IsSigned(WI.IsSigned),
LI(LInfo),
L(LI->getLoopFor(OrigPhi->getParent())),
SE(SEv),
DT(DTree),
- WidePhi(0),
- WideInc(0),
- WideIncExpr(0),
+ WidePhi(nullptr),
+ WideInc(nullptr),
+ WideIncExpr(nullptr),
DeadInsts(DI) {
assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV");
}
PHINode *CreateWideIV(SCEVExpander &Rewriter);
protected:
- Instruction *CloneIVUser(Instruction *NarrowUse,
- Instruction *NarrowDef,
- Instruction *WideDef);
+ Value *getExtend(Value *NarrowOper, Type *WideType, bool IsSigned,
+ Instruction *Use);
+
+ Instruction *CloneIVUser(NarrowIVDefUse DU);
const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse);
- Instruction *WidenIVUse(Use &NarrowDefUse, Instruction *NarrowDef,
- Instruction *WideDef);
+ const SCEVAddRecExpr* GetExtendedOperandRecurrence(NarrowIVDefUse DU);
+
+ const SCEV *GetSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
+ unsigned OpCode) const;
+
+ Instruction *WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef);
};
} // anonymous namespace
-static Value *getExtend( Value *NarrowOper, const Type *WideType,
- bool IsSigned, IRBuilder<> &Builder) {
+/// 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, const Loop *L, const DominatorTree *DT) {
+ Instruction *Inst = dyn_cast<Instruction>(V);
+ if (!Inst)
+ return true;
+
+ return DT->properlyDominates(Inst->getParent(), L->getHeader());
+}
+
+Value *WidenIV::getExtend(Value *NarrowOper, Type *WideType, bool IsSigned,
+ Instruction *Use) {
+ // Set the debug location and conservative insertion point.
+ IRBuilder<> Builder(Use);
+ // Hoist the insertion point into loop preheaders as far as possible.
+ for (const Loop *L = LI->getLoopFor(Use->getParent());
+ L && L->getLoopPreheader() && isLoopInvariant(NarrowOper, L, DT);
+ L = L->getParentLoop())
+ Builder.SetInsertPoint(L->getLoopPreheader()->getTerminator());
+
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(Instruction *NarrowUse,
- Instruction *NarrowDef,
- Instruction *WideDef) {
- unsigned Opcode = NarrowUse->getOpcode();
+Instruction *WidenIV::CloneIVUser(NarrowIVDefUse DU) {
+ unsigned Opcode = DU.NarrowUse->getOpcode();
switch (Opcode) {
default:
- return 0;
+ return nullptr;
case Instruction::Add:
case Instruction::Mul:
case Instruction::UDiv:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
- DEBUG(dbgs() << "Cloning IVUser: " << *NarrowUse << "\n");
-
- IRBuilder<> Builder(NarrowUse);
+ DEBUG(dbgs() << "Cloning IVUser: " << *DU.NarrowUse << "\n");
// 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 = (NarrowUse->getOperand(0) == NarrowDef) ? WideDef :
- getExtend(NarrowUse->getOperand(0), WideType, IsSigned, Builder);
- Value *RHS = (NarrowUse->getOperand(1) == NarrowDef) ? WideDef :
- getExtend(NarrowUse->getOperand(1), WideType, IsSigned, Builder);
+ Value *LHS = (DU.NarrowUse->getOperand(0) == DU.NarrowDef) ? DU.WideDef :
+ getExtend(DU.NarrowUse->getOperand(0), WideType, IsSigned, DU.NarrowUse);
+ Value *RHS = (DU.NarrowUse->getOperand(1) == DU.NarrowDef) ? DU.WideDef :
+ getExtend(DU.NarrowUse->getOperand(1), WideType, IsSigned, DU.NarrowUse);
- BinaryOperator *NarrowBO = cast<BinaryOperator>(NarrowUse);
+ BinaryOperator *NarrowBO = cast<BinaryOperator>(DU.NarrowUse);
BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(),
LHS, RHS,
NarrowBO->getName());
+ IRBuilder<> Builder(DU.NarrowUse);
Builder.Insert(WideBO);
if (const OverflowingBinaryOperator *OBO =
dyn_cast<OverflowingBinaryOperator>(NarrowBO)) {
}
return WideBO;
}
- llvm_unreachable(0);
}
-/// 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;
+const SCEV *WidenIV::GetSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
+ unsigned OpCode) const {
+ if (OpCode == Instruction::Add)
+ return SE->getAddExpr(LHS, RHS);
+ if (OpCode == Instruction::Sub)
+ return SE->getMinusSCEV(LHS, RHS);
+ if (OpCode == Instruction::Mul)
+ return SE->getMulExpr(LHS, RHS);
- if (!DT->dominates(InsertPos->getParent(), IncV->getParent()))
- return false;
-
- if (IncV->mayHaveSideEffects())
- return false;
+ llvm_unreachable("Unsupported opcode.");
+}
- // 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;
+/// No-wrap operations can transfer sign extension of their result to their
+/// operands. Generate the SCEV value for the widened operation without
+/// actually modifying the IR yet. If the expression after extending the
+/// operands is an AddRec for this loop, return it.
+const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
+
+ // Handle the common case of add<nsw/nuw>
+ const unsigned OpCode = DU.NarrowUse->getOpcode();
+ // Only Add/Sub/Mul instructions supported yet.
+ if (OpCode != Instruction::Add && OpCode != Instruction::Sub &&
+ OpCode != Instruction::Mul)
+ return nullptr;
+
+ // One operand (NarrowDef) has already been extended to WideDef. Now determine
+ // if extending the other will lead to a recurrence.
+ unsigned ExtendOperIdx = DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
+ assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU");
+
+ const SCEV *ExtendOperExpr = nullptr;
+ const OverflowingBinaryOperator *OBO =
+ cast<OverflowingBinaryOperator>(DU.NarrowUse);
+ if (IsSigned && OBO->hasNoSignedWrap())
+ ExtendOperExpr = SE->getSignExtendExpr(
+ SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
+ else if(!IsSigned && OBO->hasNoUnsignedWrap())
+ ExtendOperExpr = SE->getZeroExtendExpr(
+ SE->getSCEV(DU.NarrowUse->getOperand(ExtendOperIdx)), WideType);
+ else
+ return nullptr;
+
+ // When creating this SCEV expr, don't apply the current operations NSW or NUW
+ // flags. This instruction may be guarded by control flow that the no-wrap
+ // behavior depends on. Non-control-equivalent instructions can be mapped to
+ // the same SCEV expression, and it would be incorrect to transfer NSW/NUW
+ // semantics to those operations.
+ const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(
+ GetSCEVByOpCode(SE->getSCEV(DU.WideDef), ExtendOperExpr, OpCode));
+ if (!AddRec || AddRec->getLoop() != L)
+ return nullptr;
+ return AddRec;
}
-// 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.
+/// 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;
+ return nullptr;
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;
+ return nullptr;
}
const SCEV *WideExpr = IsSigned ?
SE->getZeroExtendExpr(NarrowExpr, WideType);
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr);
if (!AddRec || AddRec->getLoop() != L)
- return 0;
-
+ return nullptr;
return AddRec;
}
+/// This IV user cannot be widen. Replace this use of the original narrow IV
+/// with a truncation of the new wide IV to isolate and eliminate the narrow IV.
+static void truncateIVUse(NarrowIVDefUse DU, DominatorTree *DT) {
+ DEBUG(dbgs() << "INDVARS: Truncate IV " << *DU.WideDef
+ << " for user " << *DU.NarrowUse << "\n");
+ IRBuilder<> Builder(getInsertPointForUses(DU.NarrowUse, DU.NarrowDef, DT));
+ Value *Trunc = Builder.CreateTrunc(DU.WideDef, DU.NarrowDef->getType());
+ DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, Trunc);
+}
+
/// 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(Use &NarrowDefUse, Instruction *NarrowDef,
- Instruction *WideDef) {
- Instruction *NarrowUse = cast<Instruction>(NarrowDefUse.getUser());
+Instruction *WidenIV::WidenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
// Stop traversing the def-use chain at inner-loop phis or post-loop phis.
- if (isa<PHINode>(NarrowUse) && LI->getLoopFor(NarrowUse->getParent()) != L)
- return 0;
-
+ if (PHINode *UsePhi = dyn_cast<PHINode>(DU.NarrowUse)) {
+ if (LI->getLoopFor(UsePhi->getParent()) != L) {
+ // For LCSSA phis, sink the truncate outside the loop.
+ // After SimplifyCFG most loop exit targets have a single predecessor.
+ // Otherwise fall back to a truncate within the loop.
+ if (UsePhi->getNumOperands() != 1)
+ truncateIVUse(DU, DT);
+ else {
+ PHINode *WidePhi =
+ PHINode::Create(DU.WideDef->getType(), 1, UsePhi->getName() + ".wide",
+ UsePhi);
+ WidePhi->addIncoming(DU.WideDef, UsePhi->getIncomingBlock(0));
+ IRBuilder<> Builder(WidePhi->getParent()->getFirstInsertionPt());
+ Value *Trunc = Builder.CreateTrunc(WidePhi, DU.NarrowDef->getType());
+ UsePhi->replaceAllUsesWith(Trunc);
+ DeadInsts.push_back(UsePhi);
+ DEBUG(dbgs() << "INDVARS: Widen lcssa phi " << *UsePhi
+ << " to " << *WidePhi << "\n");
+ }
+ return nullptr;
+ }
+ }
// Our raison d'etre! Eliminate sign and zero extension.
- if (IsSigned ? isa<SExtInst>(NarrowUse) : isa<ZExtInst>(NarrowUse)) {
- Value *NewDef = WideDef;
- if (NarrowUse->getType() != WideType) {
- unsigned CastWidth = SE->getTypeSizeInBits(NarrowUse->getType());
+ 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(NarrowDefUse);
- NewDef = Builder.CreateTrunc(WideDef, NarrowUse->getType());
+ 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 " << *NarrowUse << "\n");
- NarrowUse->replaceUsesOfWith(NarrowDef, WideDef);
- NewDef = NarrowUse;
+ << " not wide enough to subsume " << *DU.NarrowUse << "\n");
+ DU.NarrowUse->replaceUsesOfWith(DU.NarrowDef, DU.WideDef);
+ NewDef = DU.NarrowUse;
}
}
- if (NewDef != NarrowUse) {
- DEBUG(dbgs() << "INDVARS: eliminating " << *NarrowUse
- << " replaced by " << *WideDef << "\n");
+ if (NewDef != DU.NarrowUse) {
+ DEBUG(dbgs() << "INDVARS: eliminating " << *DU.NarrowUse
+ << " replaced by " << *DU.WideDef << "\n");
++NumElimExt;
- NarrowUse->replaceAllUsesWith(NewDef);
- DeadInsts.push_back(NarrowUse);
+ 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
// push the uses of WideDef here.
// No further widening is needed. The deceased [sz]ext had done it for us.
- return 0;
+ return nullptr;
}
// Does this user itself evaluate to a recurrence after widening?
- const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(NarrowUse);
+ const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(DU.NarrowUse);
+ if (!WideAddRec) {
+ WideAddRec = GetExtendedOperandRecurrence(DU);
+ }
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(NarrowDefUse);
- Value *Trunc = Builder.CreateTrunc(WideDef, NarrowDef->getType());
- NarrowUse->replaceUsesOfWith(NarrowDef, Trunc);
- return 0;
+ truncateIVUse(DU, DT);
+ return nullptr;
}
- // We assume that block terminators are not SCEVable. We wouldn't want to
+ // 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(NarrowUse != NarrowUse->getParent()->getTerminator() &&
+ 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, NarrowUse, DT)) {
+ Instruction *WideUse = nullptr;
+ if (WideAddRec == WideIncExpr
+ && Rewriter.hoistIVInc(WideInc, DU.NarrowUse))
WideUse = WideInc;
- }
else {
- WideUse = CloneIVUser(NarrowUse, NarrowDef, WideDef);
+ WideUse = CloneIVUser(DU);
if (!WideUse)
- return 0;
+ return nullptr;
}
// Evaluation of WideAddRec ensured that the narrow expression could be
// extended outside the loop without overflow. This suggests that the wide use
DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse
<< ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n");
DeadInsts.push_back(WideUse);
- return 0;
+ return nullptr;
}
// Returning WideUse pushes it on the worklist.
/// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers.
///
void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
- for (Value::use_iterator UI = NarrowDef->use_begin(),
- UE = NarrowDef->use_end(); UI != UE; ++UI) {
- Use &U = UI.getUse();
+ for (User *U : NarrowDef->users()) {
+ Instruction *NarrowUser = cast<Instruction>(U);
// Handle data flow merges and bizarre phi cycles.
- if (!Widened.insert(cast<Instruction>(U.getUser())))
+ if (!Widened.insert(NarrowUser))
continue;
- NarrowIVUsers.push_back(std::make_pair(&UI.getUse(), WideDef));
+ NarrowIVUsers.push_back(NarrowIVDefUse(NarrowDef, NarrowUser, WideDef));
}
}
// Is this phi an induction variable?
const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi));
if (!AddRec)
- return NULL;
+ return nullptr;
// Widen the induction variable expression.
const SCEV *WideIVExpr = IsSigned ?
// Can the IV be extended outside the loop without overflow?
AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr);
if (!AddRec || AddRec->getLoop() != L)
- return NULL;
+ return nullptr;
// An AddRec must have loop-invariant operands. Since this AddRec is
// materialized by a loop header phi, the expression cannot have any post-loop
pushNarrowIVUsers(OrigPhi, WidePhi);
while (!NarrowIVUsers.empty()) {
- Use *UsePtr;
- Instruction *WideDef;
- tie(UsePtr, WideDef) = NarrowIVUsers.pop_back_val();
- Use &NarrowDefUse = *UsePtr;
+ 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 *NarrowDef = cast<Instruction>(NarrowDefUse.get());
- Instruction *WideUse = WidenIVUse(NarrowDefUse, NarrowDef, WideDef);
+ Instruction *WideUse = WidenIVUse(DU, Rewriter);
// Follow all def-use edges from the previous narrow use.
if (WideUse)
- pushNarrowIVUsers(cast<Instruction>(NarrowDefUse.getUser()), WideUse);
+ pushNarrowIVUsers(DU.NarrowUse, WideUse);
// WidenIVUse may have removed the def-use edge.
- if (NarrowDef->use_empty())
- DeadInsts.push_back(NarrowDef);
+ if (DU.NarrowDef->use_empty())
+ DeadInsts.push_back(DU.NarrowDef);
}
return WidePhi;
}
//===----------------------------------------------------------------------===//
-// Simplification of IV users based on SCEV evaluation.
+// Live IV Reduction - Minimize IVs live across the loop.
//===----------------------------------------------------------------------===//
-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;
-
- 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 (!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);
- }
+//===----------------------------------------------------------------------===//
+// Simplification of IV users based on SCEV evaluation.
+//===----------------------------------------------------------------------===//
- // 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);
-}
+namespace {
+ class IndVarSimplifyVisitor : public IVVisitor {
+ ScalarEvolution *SE;
+ const DataLayout *DL;
+ PHINode *IVPhi;
-/// 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;
+ public:
+ WideIVInfo WI;
+
+ IndVarSimplifyVisitor(PHINode *IV, ScalarEvolution *SCEV,
+ const DataLayout *DL, const DominatorTree *DTree):
+ SE(SCEV), DL(DL), IVPhi(IV) {
+ DT = DTree;
+ WI.NarrowIV = IVPhi;
+ if (ReduceLiveIVs)
+ setSplitOverflowIntrinsics();
}
- }
-
- // 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);
-
- // We assume that terminators are not SCEVable.
- assert((!S || I != I->getParent()->getTerminator()) &&
- "can't fold terminators");
- // Only consider affine recurrences.
- const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S);
- if (AR && AR->getLoop() == L)
- return true;
-
- return false;
+ // Implement the interface used by simplifyUsersOfIV.
+ void visitCast(CastInst *Cast) override { visitIVCast(Cast, WI, SE, DL); }
+ };
}
-/// SimplifyIVUsersNoRewrite - Iteratively perform simplification on a worklist
-/// of IV users. Each successive simplification may push more users which may
+/// SimplifyAndExtend - 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.
+/// Sign/Zero extend elimination is interleaved with IV simplification.
///
-void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) {
- std::map<PHINode *, WideIVInfo> WideIVMap;
+void IndVarSimplify::SimplifyAndExtend(Loop *L,
+ SCEVExpander &Rewriter,
+ LPPassManager &LPM) {
+ SmallVector<WideIVInfo, 8> WideIVs;
SmallVector<PHINode*, 8> LoopPhis;
for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
// 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.
+ // other SCEV based analysis prior to SimplifyAndExtend.
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;
+ IndVarSimplifyVisitor Visitor(CurrIV, SE, DL, DT);
- // Use-def pairs if IV users waiting to be processed for CurrIV.
- SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;
+ Changed |= simplifyUsersOfIV(CurrIV, SE, &LPM, DeadInsts, &Visitor);
- // 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()) {
- Instruction *UseInst, *Operand;
- tie(UseInst, Operand) = SimpleIVUsers.pop_back_val();
- // Bypass back edges to avoid extra work.
- if (UseInst == CurrIV) continue;
-
- if (EliminateIVUser(UseInst, Operand)) {
- pushIVUsers(Operand, Simplified, SimpleIVUsers);
- continue;
- }
- if (CastInst *Cast = dyn_cast<CastInst>(UseInst)) {
- bool IsSigned = Cast->getOpcode() == Instruction::SExt;
- if (IsSigned || Cast->getOpcode() == Instruction::ZExt) {
- CollectExtend(Cast, IsSigned, WI, SE, TD);
- }
- continue;
- }
- if (isSimpleIVUser(UseInst, L, SE)) {
- pushIVUsers(UseInst, Simplified, SimpleIVUsers);
- }
- }
- if (WI.WidestNativeType) {
- WideIVMap[CurrIV] = WI;
+ if (Visitor.WI.WidestNativeType) {
+ WideIVs.push_back(Visitor.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);
+ for (; !WideIVs.empty(); WideIVs.pop_back()) {
+ WidenIV Widener(WideIVs.back(), 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;
+//===----------------------------------------------------------------------===//
+// LinearFunctionTestReplace and its kin. Rewrite the loop exit condition.
+//===----------------------------------------------------------------------===//
- const SCEV *S = SE->getSCEV(Phi);
- DenseMap<const SCEV *, PHINode *>::const_iterator Pos;
- bool Inserted;
- tie(Pos, Inserted) = ExprToIVMap.insert(std::make_pair(S, Phi));
- if (Inserted)
- continue;
- PHINode *OrigPhi = Pos->second;
- // 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 &&
- 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);
- }
+/// 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,
+ SmallPtrSetImpl<const SCEV*> &Processed,
+ ScalarEvolution *SE) {
+ if (!Processed.insert(S))
+ return false;
+
+ // 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;
}
- 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.
-//===----------------------------------------------------------------------===//
+ // 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, Processed, 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 pattern, assume it's 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.
+///
+/// TODO: This fails for pointer-type loop counters with greater than one byte
+/// strides, consequently preventing LFTR from running. For the purpose of LFTR
+/// we could skip this check in the case that the LFTR loop counter (chosen by
+/// FindLoopCounter) is also pointer type. Instead, we could directly convert
+/// the loop test to an inequality test by checking the target data's alignment
+/// of element types (given that the initial pointer value originates from or is
+/// used by ABI constrained operation, as opposed to inttoptr/ptrtoint).
+/// However, we don't yet have a strong motivation for converting loop tests
+/// into inequality tests.
static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) {
const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) ||
if (!BI)
return false;
- // 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 false;
- 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 false;
- }
- }
+ SmallPtrSet<const SCEV*, 8> Processed;
+ if (isHighCostExpansion(BackedgeTakenCount, BI, Processed, SE))
+ return false;
+
return true;
}
-/// getBackedgeIVType - Get the widest type used by the loop test after peeking
-/// through Truncs.
-///
-/// TODO: Unnecessary if LFTR does not force a canonical IV.
-static const Type *getBackedgeIVType(Loop *L) {
- if (!L->getExitingBlock())
- return 0;
+/// 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 nullptr;
+
+ 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 nullptr;
+ }
+
+ PHINode *Phi = dyn_cast<PHINode>(IncI->getOperand(0));
+ if (Phi && Phi->getParent() == L->getHeader()) {
+ if (isLoopInvariant(IncI->getOperand(1), L, DT))
+ return Phi;
+ return nullptr;
+ }
+ if (IncI->getOpcode() == Instruction::GetElementPtr)
+ return nullptr;
+
+ // 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 nullptr;
+}
+
+/// Return the compare guarding the loop latch, or NULL for unrecognized tests.
+static ICmpInst *getLoopTest(Loop *L) {
+ 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 nullptr;
- // Can't rewrite non-branch yet.
BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator());
- if (!BI)
- return 0;
+ assert(BI && "expected exit branch");
+
+ return dyn_cast<ICmpInst>(BI->getCondition());
+}
- ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
+/// 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) {
+ // Do LFTR to simplify the exit condition to an ICMP.
+ ICmpInst *Cond = getLoopTest(L);
if (!Cond)
- return 0;
-
- const 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)
+ 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 PHI node is defined in the loop, but is *not* a counter.
+ int Idx = Phi->getBasicBlockIndex(L->getLoopLatch());
+ if (Idx < 0)
+ return true;
+
+ // Do LFTR if the exit condition's IV is *not* a simple counter.
+ Value *IncV = Phi->getIncomingValue(Idx);
+ return Phi != getLoopPhiForCounter(IncV, L, DT);
+}
+
+/// Recursive helper for hasConcreteDef(). Unfortunately, this currently boils
+/// down to checking that all operands are constant and listing instructions
+/// that may hide undef.
+static bool hasConcreteDefImpl(Value *V, SmallPtrSetImpl<Value*> &Visited,
+ unsigned Depth) {
+ if (isa<Constant>(V))
+ return !isa<UndefValue>(V);
+
+ if (Depth >= 6)
+ return false;
+
+ // Conservatively handle non-constant non-instructions. For example, Arguments
+ // may be undef.
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I)
+ return false;
+
+ // Load and return values may be undef.
+ if(I->mayReadFromMemory() || isa<CallInst>(I) || isa<InvokeInst>(I))
+ return false;
+
+ // Optimistically handle other instructions.
+ for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) {
+ if (!Visited.insert(*OI))
+ continue;
+ if (!hasConcreteDefImpl(*OI, Visited, Depth+1))
+ return false;
+ }
+ return true;
+}
+
+/// Return true if the given value is concrete. We must prove that undef can
+/// never reach it.
+///
+/// TODO: If we decide that this is a good approach to checking for undef, we
+/// may factor it into a common location.
+static bool hasConcreteDef(Value *V) {
+ SmallPtrSet<Value*, 8> Visited;
+ Visited.insert(V);
+ return hasConcreteDefImpl(V, Visited, 0);
+}
+
+/// 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 (User *U : Phi->users())
+ if (U != Cond && U != IncV) return false;
+
+ for (User *U : IncV->users())
+ if (U != Cond && U != Phi) return false;
+ return true;
+}
+
+/// FindLoopCounter - Find an affine IV in canonical form.
+///
+/// BECount may be an i8* pointer type. The pointer difference is already
+/// valid count without scaling the address stride, so it remains a pointer
+/// expression as far as SCEV is concerned.
+///
+/// Currently only valid for LFTR. See the comments on hasConcreteDef below.
+///
+/// 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 DataLayout *DL) {
+ 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 = nullptr;
+ const SCEV *BestInit = nullptr;
+ 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;
+
+ // Avoid comparing an integer IV against a pointer Limit.
+ if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy())
+ 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 || (DL && !DL->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;
- return Trunc->getSrcTy();
+ // Avoid reusing a potentially undef value to compute other values that may
+ // have originally had a concrete definition.
+ if (!hasConcreteDef(Phi)) {
+ // We explicitly allow unknown phis as long as they are already used by
+ // the loop test. In this case we assume that performing LFTR could not
+ // increase the number of undef users.
+ if (ICmpInst *Cond = getLoopTest(L)) {
+ if (Phi != getLoopPhiForCounter(Cond->getOperand(0), L, DT)
+ && Phi != getLoopPhiForCounter(Cond->getOperand(1), L, DT)) {
+ 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.
+ else if (PhiWidth <= SE->getTypeSizeInBits(BestPhi->getType()))
+ continue;
+ }
+ BestPhi = Phi;
+ BestInit = Init;
+ }
+ return BestPhi;
+}
+
+/// genLoopLimit - Help LinearFunctionTestReplace by generating a value that
+/// holds the RHS of the new loop test.
+static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
+ SCEVExpander &Rewriter, ScalarEvolution *SE) {
+ const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
+ assert(AR && AR->getLoop() == L && AR->isAffine() && "bad loop counter");
+ const SCEV *IVInit = AR->getStart();
+
+ // IVInit may be a pointer while IVCount is an integer when FindLoopCounter
+ // finds a valid pointer IV. Sign extend BECount in order to materialize a
+ // GEP. Avoid running SCEVExpander on a new pointer value, instead reusing
+ // the existing GEPs whenever possible.
+ if (IndVar->getType()->isPointerTy()
+ && !IVCount->getType()->isPointerTy()) {
+
+ // IVOffset will be the new GEP offset that is interpreted by GEP as a
+ // signed value. IVCount on the other hand represents the loop trip count,
+ // which is an unsigned value. FindLoopCounter only allows induction
+ // variables that have a positive unit stride of one. This means we don't
+ // have to handle the case of negative offsets (yet) and just need to zero
+ // extend IVCount.
+ Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType());
+ const SCEV *IVOffset = SE->getTruncateOrZeroExtend(IVCount, OfsTy);
+
+ // Expand the code for the iteration count.
+ assert(SE->isLoopInvariant(IVOffset, L) &&
+ "Computed iteration count is not loop invariant!");
+ BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
+ Value *GEPOffset = Rewriter.expandCodeFor(IVOffset, OfsTy, BI);
+
+ Value *GEPBase = IndVar->getIncomingValueForBlock(L->getLoopPreheader());
+ assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter");
+ // We could handle pointer IVs other than i8*, but we need to compensate for
+ // gep index scaling. See canExpandBackedgeTakenCount comments.
+ assert(SE->getSizeOfExpr(IntegerType::getInt64Ty(IndVar->getContext()),
+ cast<PointerType>(GEPBase->getType())->getElementType())->isOne()
+ && "unit stride pointer IV must be i8*");
+
+ IRBuilder<> Builder(L->getLoopPreheader()->getTerminator());
+ return Builder.CreateGEP(GEPBase, GEPOffset, "lftr.limit");
+ }
+ else {
+ // In any other case, convert both IVInit and IVCount to integers before
+ // comparing. This may result in SCEV expension of pointers, but in practice
+ // SCEV will fold the pointer arithmetic away as such:
+ // BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc).
+ //
+ // Valid Cases: (1) both integers is most common; (2) both may be pointers
+ // for simple memset-style loops.
+ //
+ // IVInit integer and IVCount pointer would only occur if a canonical IV
+ // were generated on top of case #2, which is not expected.
+
+ const SCEV *IVLimit = nullptr;
+ // For unit stride, IVCount = Start + BECount with 2's complement overflow.
+ // For non-zero Start, compute IVCount here.
+ if (AR->getStart()->isZero())
+ IVLimit = IVCount;
+ else {
+ assert(AR->getStepRecurrence(*SE)->isOne() && "only handles unit stride");
+ const SCEV *IVInit = AR->getStart();
+
+ // For integer IVs, truncate the IV before computing IVInit + BECount.
+ if (SE->getTypeSizeInBits(IVInit->getType())
+ > SE->getTypeSizeInBits(IVCount->getType()))
+ IVInit = SE->getTruncateExpr(IVInit, IVCount->getType());
+
+ IVLimit = SE->getAddExpr(IVInit, IVCount);
+ }
+ // Expand the code for the iteration count.
+ BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
+ IRBuilder<> Builder(BI);
+ assert(SE->isLoopInvariant(IVLimit, L) &&
+ "Computed iteration count is not loop invariant!");
+ // Ensure that we generate the same type as IndVar, or a smaller integer
+ // type. In the presence of null pointer values, we have an integer type
+ // SCEV expression (IVInit) for a pointer type IV value (IndVar).
+ Type *LimitTy = IVCount->getType()->isPointerTy() ?
+ IndVar->getType() : IVCount->getType();
+ return Rewriter.expandCodeFor(IVLimit, LimitTy, BI);
}
- return Ty;
}
/// LinearFunctionTestReplace - This method rewrites the exit condition of the
/// 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::
+Value *IndVarSimplify::
LinearFunctionTestReplace(Loop *L,
const SCEV *BackedgeTakenCount,
PHINode *IndVar,
SCEVExpander &Rewriter) {
assert(canExpandBackedgeTakenCount(L, SE) && "precondition");
- BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
- // 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 (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 *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0);
- const SCEV *N =
- SE->getAddExpr(BackedgeTakenCount,
- SE->getConstant(BackedgeTakenCount->getType(), 1));
- 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->getConstant(IndVar->getType(), 1));
- }
+ // Initialize CmpIndVar and IVCount to their preincremented values.
+ Value *CmpIndVar = IndVar;
+ const SCEV *IVCount = BackedgeTakenCount;
+ // If the exiting block is the same as the backedge block, we prefer to
+ // compare against the post-incremented value, otherwise we must compare
+ // against the preincremented value.
+ if (L->getExitingBlock() == L->getLoopLatch()) {
// 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 {
- // We have to use the preincremented value...
- RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount,
- IndVar->getType());
- CmpIndVar = IndVar;
+ llvm::Value *IncrementedIndvar =
+ IndVar->getIncomingValueForBlock(L->getExitingBlock());
+ const auto *IncrementedIndvarSCEV =
+ cast<SCEVAddRecExpr>(SE->getSCEV(IncrementedIndvar));
+ // It is unsafe to use the incremented indvar if it has a wrapping flag, we
+ // don't want to compare against a poison value. Check the SCEV that
+ // corresponds to the incremented indvar, the SCEVExpander will only insert
+ // flags in the IR if the SCEV originally had wrapping flags.
+ // FIXME: In theory, SCEV could drop flags even though they exist in IR.
+ // A more robust solution would involve getting a new expression for
+ // CmpIndVar by applying non-NSW/NUW AddExprs.
+ if (!ScalarEvolution::maskFlags(IncrementedIndvarSCEV->getNoWrapFlags(),
+ SCEV::FlagNUW | SCEV::FlagNSW)) {
+ // Add one to the "backedge-taken" count to get the trip count.
+ // This addition may overflow, which is valid as long as the comparison is
+ // truncated to BackedgeTakenCount->getType().
+ IVCount =
+ SE->getAddExpr(BackedgeTakenCount,
+ SE->getConstant(BackedgeTakenCount->getType(), 1));
+ CmpIndVar = IncrementedIndvar;
+ }
}
- // Expand the code for the iteration count.
- assert(SE->isLoopInvariant(RHS, L) &&
- "Computed iteration count is not loop invariant!");
- Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI);
+ Value *ExitCnt = genLoopLimit(IndVar, IVCount, L, Rewriter, SE);
+ assert(ExitCnt->getType()->isPointerTy() == IndVar->getType()->isPointerTy()
+ && "genLoopLimit missed a cast");
// Insert a new icmp_ne or icmp_eq instruction before the branch.
- ICmpInst::Predicate Opcode;
+ BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator());
+ ICmpInst::Predicate P;
if (L->contains(BI->getSuccessor(0)))
- Opcode = ICmpInst::ICMP_NE;
+ P = ICmpInst::ICMP_NE;
else
- Opcode = ICmpInst::ICMP_EQ;
+ P = ICmpInst::ICMP_EQ;
DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n"
<< " LHS:" << *CmpIndVar << '\n'
<< " op:\t"
- << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
- << " RHS:\t" << *RHS << "\n");
+ << (P == ICmpInst::ICMP_NE ? "!=" : "==") << "\n"
+ << " RHS:\t" << *ExitCnt << "\n"
+ << " IVCount:\t" << *IVCount << "\n");
+
+ IRBuilder<> Builder(BI);
+
+ // LFTR can ignore IV overflow and truncate to the width of
+ // BECount. This avoids materializing the add(zext(add)) expression.
+ unsigned CmpIndVarSize = SE->getTypeSizeInBits(CmpIndVar->getType());
+ unsigned ExitCntSize = SE->getTypeSizeInBits(ExitCnt->getType());
+ if (CmpIndVarSize > ExitCntSize) {
+ const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(SE->getSCEV(IndVar));
+ const SCEV *ARStart = AR->getStart();
+ const SCEV *ARStep = AR->getStepRecurrence(*SE);
+ // For constant IVCount, avoid truncation.
+ if (isa<SCEVConstant>(ARStart) && isa<SCEVConstant>(IVCount)) {
+ const APInt &Start = cast<SCEVConstant>(ARStart)->getValue()->getValue();
+ APInt Count = cast<SCEVConstant>(IVCount)->getValue()->getValue();
+ // Note that the post-inc value of BackedgeTakenCount may have overflowed
+ // above such that IVCount is now zero.
+ if (IVCount != BackedgeTakenCount && Count == 0) {
+ Count = APInt::getMaxValue(Count.getBitWidth()).zext(CmpIndVarSize);
+ ++Count;
+ }
+ else
+ Count = Count.zext(CmpIndVarSize);
+ APInt NewLimit;
+ if (cast<SCEVConstant>(ARStep)->getValue()->isNegative())
+ NewLimit = Start - Count;
+ else
+ NewLimit = Start + Count;
+ ExitCnt = ConstantInt::get(CmpIndVar->getType(), NewLimit);
- ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond");
- Cond->setDebugLoc(BI->getDebugLoc());
+ DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n");
+ } else {
+ CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
+ "lftr.wideiv");
+ }
+ }
+ 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
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) return;
- Instruction *InsertPt = ExitBlock->getFirstNonPHI();
+ Instruction *InsertPt = ExitBlock->getFirstInsertionPt();
BasicBlock::iterator I = Preheader->getTerminator();
while (I != Preheader->begin()) {
--I;
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;
+ // Skip landingpad instructions.
+ if (isa<LandingPadInst>(I))
+ continue;
+
+ // Don't sink alloca: we never want to sink static alloca's out of the
+ // entry block, and correctly sinking dynamic alloca's requires
+ // checks for stacksave/stackrestore intrinsics.
+ // FIXME: Refactor this check somehow?
+ if (isa<AllocaInst>(I))
+ 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)) {
+ for (Use &U : I->uses()) {
+ Instruction *User = cast<Instruction>(U.getUser());
+ BasicBlock *UseBB = User->getParent();
+ if (PHINode *P = dyn_cast<PHINode>(User)) {
unsigned i =
- PHINode::getIncomingValueNumForOperand(UI.getOperandNo());
+ PHINode::getIncomingValueNumForOperand(U.getOperandNo());
UseBB = P->getIncomingBlock(i);
}
if (UseBB == Preheader || L->contains(UseBB)) {
//===----------------------------------------------------------------------===//
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
+ if (skipOptnoneFunction(L))
+ return false;
+
// 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"
if (!L->isLoopSimplifyForm())
return false;
- if (!DisableIVRewrite)
- IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
SE = &getAnalysis<ScalarEvolution>();
- DT = &getAnalysis<DominatorTree>();
- TD = getAnalysisIfAvailable<TargetData>();
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
+ DL = DLP ? &DLP->getDataLayout() : nullptr;
+ TLI = getAnalysisIfAvailable<TargetLibraryInfo>();
DeadInsts.clear();
Changed = false;
// Create a rewriter object which we'll use to transform the code with.
SCEVExpander Rewriter(*SE, "indvars");
+#ifndef NDEBUG
+ Rewriter.setDebugType(DEBUG_TYPE);
+#endif
// Eliminate redundant IV users.
//
// 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);
- }
+ Rewriter.disableCanonicalMode();
+ SimplifyAndExtend(L, Rewriter, LPM);
// 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
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.
- const Type *LargestType = 0;
- bool NeedCannIV = false;
- bool ExpandBECount = canExpandBackedgeTakenCount(L, SE);
- if (ExpandBECount) {
- // 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;
- const 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;
- const 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());
- }
- }
+ NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts);
// 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 (ExpandBECount) {
- assert(canExpandBackedgeTakenCount(L, SE) &&
- "canonical IV disrupted BackedgeTaken expansion");
- assert(NeedCannIV &&
- "LinearFunctionTestReplace requires a canonical induction variable");
- // 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);
+ if (canExpandBackedgeTakenCount(L, SE) && needsLFTR(L, DT)) {
+ PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT, DL);
+ if (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())
+ (void)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.
while (!DeadInsts.empty())
if (Instruction *Inst =
dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val()))
- RecursivelyDeleteTriviallyDeadInstructions(Inst);
+ RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
// The Rewriter may not be used from this point on.
// 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 (NewICmp && IU)
- IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0)));
-
// Clean up dead instructions.
- Changed |= DeleteDeadPHIs(L->getHeader());
+ Changed |= DeleteDeadPHIs(L->getHeader(), TLI);
// Check a post-condition.
- assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!");
+ 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 (VerifyIndvars && !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;
}
projects / oota-llvm.git / blobdiff