//
// Limitations and TODO items:
//
-// 1) We only considers n-ary adds for now. This should be extended and
-// generalized.
-//
-// 2) Besides arithmetic operations, similar reassociation can be applied to
-// GEPs. For example, if
-// X = &arr[a]
-// dominates
-// Y = &arr[a + b]
-// we may rewrite Y into X + b.
+// 1) We only considers n-ary adds and muls for now. This should be extended
+// and generalized.
//
//===----------------------------------------------------------------------===//
+#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PatternMatch.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addPreserved<DominatorTreeWrapperPass>();
- AU.addPreserved<ScalarEvolution>();
+ AU.addPreserved<ScalarEvolutionWrapperPass>();
AU.addPreserved<TargetLibraryInfoWrapperPass>();
+ AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
- AU.addRequired<ScalarEvolution>();
+ AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.setPreservesCFG();
unsigned I, Value *LHS,
Value *RHS, Type *IndexedType);
- // Reassociate Add for better CSE.
- Instruction *tryReassociateAdd(BinaryOperator *I);
- // A helper function for tryReassociateAdd. LHS and RHS are explicitly passed.
- Instruction *tryReassociateAdd(Value *LHS, Value *RHS, Instruction *I);
- // Rewrites I to LHS + RHS if LHS is computed already.
- Instruction *tryReassociatedAdd(const SCEV *LHS, Value *RHS, Instruction *I);
+ // Reassociate binary operators for better CSE.
+ Instruction *tryReassociateBinaryOp(BinaryOperator *I);
+
+ // A helper function for tryReassociateBinaryOp. LHS and RHS are explicitly
+ // passed.
+ Instruction *tryReassociateBinaryOp(Value *LHS, Value *RHS,
+ BinaryOperator *I);
+ // Rewrites I to (LHS op RHS) if LHS is computed already.
+ Instruction *tryReassociatedBinaryOp(const SCEV *LHS, Value *RHS,
+ BinaryOperator *I);
+
+ // Tries to match Op1 and Op2 by using V.
+ bool matchTernaryOp(BinaryOperator *I, Value *V, Value *&Op1, Value *&Op2);
+
+ // Gets SCEV for (LHS op RHS).
+ const SCEV *getBinarySCEV(BinaryOperator *I, const SCEV *LHS,
+ const SCEV *RHS);
// Returns the closest dominator of \c Dominatee that computes
// \c CandidateExpr. Returns null if not found.
// to be an index of GEP.
bool requiresSignExtension(Value *Index, GetElementPtrInst *GEP);
+ AssumptionCache *AC;
+ const DataLayout *DL;
DominatorTree *DT;
ScalarEvolution *SE;
TargetLibraryInfo *TLI;
TargetTransformInfo *TTI;
- const DataLayout *DL;
// A lookup table quickly telling which instructions compute the given SCEV.
// Note that there can be multiple instructions at different locations
// computing to the same SCEV, so we map a SCEV to an instruction list. For
// foo(a + b);
// if (p2)
// bar(a + b);
- DenseMap<const SCEV *, SmallVector<Instruction *, 2>> SeenExprs;
+ DenseMap<const SCEV *, SmallVector<WeakVH, 2>> SeenExprs;
};
} // anonymous namespace
char NaryReassociate::ID = 0;
INITIALIZE_PASS_BEGIN(NaryReassociate, "nary-reassociate", "Nary reassociation",
false, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(NaryReassociate, "nary-reassociate", "Nary reassociation",
if (skipOptnoneFunction(F))
return false;
+ AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
- SE = &getAnalysis<ScalarEvolution>();
+ SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::GetElementPtr:
+ case Instruction::Mul:
return true;
default:
return false;
Node != GraphTraits<DominatorTree *>::nodes_end(DT); ++Node) {
BasicBlock *BB = Node->getBlock();
for (auto I = BB->begin(); I != BB->end(); ++I) {
- if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(I)) {
- const SCEV *OldSCEV = SE->getSCEV(I);
- if (Instruction *NewI = tryReassociate(I)) {
+ if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(&*I)) {
+ const SCEV *OldSCEV = SE->getSCEV(&*I);
+ if (Instruction *NewI = tryReassociate(&*I)) {
Changed = true;
- SE->forgetValue(I);
+ SE->forgetValue(&*I);
I->replaceAllUsesWith(NewI);
- RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
- I = NewI;
+ // If SeenExprs constains I's WeakVH, that entry will be replaced with
+ // nullptr.
+ RecursivelyDeleteTriviallyDeadInstructions(&*I, TLI);
+ I = NewI->getIterator();
}
// Add the rewritten instruction to SeenExprs; the original instruction
// is deleted.
- const SCEV *NewSCEV = SE->getSCEV(I);
- SeenExprs[NewSCEV].push_back(I);
+ const SCEV *NewSCEV = SE->getSCEV(&*I);
+ SeenExprs[NewSCEV].push_back(WeakVH(&*I));
// Ideally, NewSCEV should equal OldSCEV because tryReassociate(I)
// is equivalent to I. However, ScalarEvolution::getSCEV may
// weaken nsw causing NewSCEV not to equal OldSCEV. For example, suppose
//
// This improvement is exercised in @reassociate_gep_nsw in nary-gep.ll.
if (NewSCEV != OldSCEV)
- SeenExprs[OldSCEV].push_back(I);
+ SeenExprs[OldSCEV].push_back(WeakVH(&*I));
}
}
}
Instruction *NaryReassociate::tryReassociate(Instruction *I) {
switch (I->getOpcode()) {
case Instruction::Add:
- return tryReassociateAdd(cast<BinaryOperator>(I));
+ case Instruction::Mul:
+ return tryReassociateBinaryOp(cast<BinaryOperator>(I));
case Instruction::GetElementPtr:
return tryReassociateGEP(cast<GetElementPtrInst>(I));
default:
NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
Type *IndexedType) {
Value *IndexToSplit = GEP->getOperand(I + 1);
- if (SExtInst *SExt = dyn_cast<SExtInst>(IndexToSplit))
+ if (SExtInst *SExt = dyn_cast<SExtInst>(IndexToSplit)) {
IndexToSplit = SExt->getOperand(0);
+ } else if (ZExtInst *ZExt = dyn_cast<ZExtInst>(IndexToSplit)) {
+ // zext can be treated as sext if the source is non-negative.
+ if (isKnownNonNegative(ZExt->getOperand(0), *DL, 0, AC, GEP, DT))
+ IndexToSplit = ZExt->getOperand(0);
+ }
if (AddOperator *AO = dyn_cast<AddOperator>(IndexToSplit)) {
// If the I-th index needs sext and the underlying add is not equipped with
// nsw, we cannot split the add because
// sext(LHS + RHS) != sext(LHS) + sext(RHS).
- if (requiresSignExtension(IndexToSplit, GEP) && !AO->hasNoSignedWrap())
+ if (requiresSignExtension(IndexToSplit, GEP) &&
+ computeOverflowForSignedAdd(AO, *DL, AC, GEP, DT) !=
+ OverflowResult::NeverOverflows)
return nullptr;
+
Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
// IndexToSplit = LHS + RHS.
if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I, LHS, RHS, IndexedType))
return nullptr;
}
-GetElementPtrInst *
-NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
- Value *LHS, Value *RHS,
- Type *IndexedType) {
+GetElementPtrInst *NaryReassociate::tryReassociateGEPAtIndex(
+ GetElementPtrInst *GEP, unsigned I, Value *LHS, Value *RHS,
+ Type *IndexedType) {
// Look for GEP's closest dominator that has the same SCEV as GEP except that
// the I-th index is replaced with LHS.
SmallVector<const SCEV *, 4> IndexExprs;
IndexExprs.push_back(SE->getSCEV(*Index));
// Replace the I-th index with LHS.
IndexExprs[I] = SE->getSCEV(LHS);
+ if (isKnownNonNegative(LHS, *DL, 0, AC, GEP, DT) &&
+ DL->getTypeSizeInBits(LHS->getType()) <
+ DL->getTypeSizeInBits(GEP->getOperand(I)->getType())) {
+ // Zero-extend LHS if it is non-negative. InstCombine canonicalizes sext to
+ // zext if the source operand is proved non-negative. We should do that
+ // consistently so that CandidateExpr more likely appears before. See
+ // @reassociate_gep_assume for an example of this canonicalization.
+ IndexExprs[I] =
+ SE->getZeroExtendExpr(IndexExprs[I], GEP->getOperand(I)->getType());
+ }
const SCEV *CandidateExpr = SE->getGEPExpr(
GEP->getSourceElementType(), SE->getSCEV(GEP->getPointerOperand()),
IndexExprs, GEP->isInBounds());
return NewGEP;
}
-Instruction *NaryReassociate::tryReassociateAdd(BinaryOperator *I) {
+Instruction *NaryReassociate::tryReassociateBinaryOp(BinaryOperator *I) {
Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
- if (auto *NewI = tryReassociateAdd(LHS, RHS, I))
+ if (auto *NewI = tryReassociateBinaryOp(LHS, RHS, I))
return NewI;
- if (auto *NewI = tryReassociateAdd(RHS, LHS, I))
+ if (auto *NewI = tryReassociateBinaryOp(RHS, LHS, I))
return NewI;
return nullptr;
}
-Instruction *NaryReassociate::tryReassociateAdd(Value *LHS, Value *RHS,
- Instruction *I) {
+Instruction *NaryReassociate::tryReassociateBinaryOp(Value *LHS, Value *RHS,
+ BinaryOperator *I) {
Value *A = nullptr, *B = nullptr;
- // To be conservative, we reassociate I only when it is the only user of A+B.
- if (LHS->hasOneUse() && match(LHS, m_Add(m_Value(A), m_Value(B)))) {
- // I = (A + B) + RHS
- // = (A + RHS) + B or (B + RHS) + A
+ // To be conservative, we reassociate I only when it is the only user of (A op
+ // B).
+ if (LHS->hasOneUse() && matchTernaryOp(I, LHS, A, B)) {
+ // I = (A op B) op RHS
+ // = (A op RHS) op B or (B op RHS) op A
const SCEV *AExpr = SE->getSCEV(A), *BExpr = SE->getSCEV(B);
const SCEV *RHSExpr = SE->getSCEV(RHS);
if (BExpr != RHSExpr) {
- if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(AExpr, RHSExpr), B, I))
+ if (auto *NewI =
+ tryReassociatedBinaryOp(getBinarySCEV(I, AExpr, RHSExpr), B, I))
return NewI;
}
if (AExpr != RHSExpr) {
- if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(BExpr, RHSExpr), A, I))
+ if (auto *NewI =
+ tryReassociatedBinaryOp(getBinarySCEV(I, BExpr, RHSExpr), A, I))
return NewI;
}
}
return nullptr;
}
-Instruction *NaryReassociate::tryReassociatedAdd(const SCEV *LHSExpr,
- Value *RHS, Instruction *I) {
- auto Pos = SeenExprs.find(LHSExpr);
- // Bail out if LHSExpr is not previously seen.
- if (Pos == SeenExprs.end())
- return nullptr;
-
+Instruction *NaryReassociate::tryReassociatedBinaryOp(const SCEV *LHSExpr,
+ Value *RHS,
+ BinaryOperator *I) {
// Look for the closest dominator LHS of I that computes LHSExpr, and replace
- // I with LHS + RHS.
+ // I with LHS op RHS.
auto *LHS = findClosestMatchingDominator(LHSExpr, I);
if (LHS == nullptr)
return nullptr;
- Instruction *NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
+ Instruction *NewI = nullptr;
+ switch (I->getOpcode()) {
+ case Instruction::Add:
+ NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
+ break;
+ case Instruction::Mul:
+ NewI = BinaryOperator::CreateMul(LHS, RHS, "", I);
+ break;
+ default:
+ llvm_unreachable("Unexpected instruction.");
+ }
NewI->takeName(I);
return NewI;
}
+bool NaryReassociate::matchTernaryOp(BinaryOperator *I, Value *V, Value *&Op1,
+ Value *&Op2) {
+ switch (I->getOpcode()) {
+ case Instruction::Add:
+ return match(V, m_Add(m_Value(Op1), m_Value(Op2)));
+ case Instruction::Mul:
+ return match(V, m_Mul(m_Value(Op1), m_Value(Op2)));
+ default:
+ llvm_unreachable("Unexpected instruction.");
+ }
+ return false;
+}
+
+const SCEV *NaryReassociate::getBinarySCEV(BinaryOperator *I, const SCEV *LHS,
+ const SCEV *RHS) {
+ switch (I->getOpcode()) {
+ case Instruction::Add:
+ return SE->getAddExpr(LHS, RHS);
+ case Instruction::Mul:
+ return SE->getMulExpr(LHS, RHS);
+ default:
+ llvm_unreachable("Unexpected instruction.");
+ }
+ return nullptr;
+}
+
Instruction *
NaryReassociate::findClosestMatchingDominator(const SCEV *CandidateExpr,
Instruction *Dominatee) {
// future instruction either. Therefore, we pop it out of the stack. This
// optimization makes the algorithm O(n).
while (!Candidates.empty()) {
- Instruction *Candidate = Candidates.back();
- if (DT->dominates(Candidate, Dominatee))
- return Candidate;
+ // Candidates stores WeakVHs, so a candidate can be nullptr if it's removed
+ // during rewriting.
+ if (Value *Candidate = Candidates.back()) {
+ Instruction *CandidateInstruction = cast<Instruction>(Candidate);
+ if (DT->dominates(CandidateInstruction, Dominatee))
+ return CandidateInstruction;
+ }
Candidates.pop_back();
}
return nullptr;
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