[llvm] r237971 - [NaryReassoc] reassociate GEP for CSE
Jingyue Wu
jingyue at google.com
Thu May 21 16:17:30 PDT 2015
Author: jingyue
Date: Thu May 21 18:17:30 2015
New Revision: 237971
URL: http://llvm.org/viewvc/llvm-project?rev=237971&view=rev
Log:
[NaryReassoc] reassociate GEP for CSE
Summary:
x = &a[i];
y = &a[i + j];
=>
y = x + j;
along with some refactoring work such as extracting method
findClosestMatchingDominator.
Depends on D9786 which provides the ScalarEvolution::getGEPExpr interface.
Test Plan: nary-gep.ll
Reviewers: meheff, broune
Reviewed By: broune
Subscribers: jholewinski, llvm-commits
Differential Revision: http://reviews.llvm.org/D9802
Added:
llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp?rev=237971&r1=237970&r2=237971&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp Thu May 21 18:17:30 2015
@@ -85,6 +85,7 @@
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PatternMatch.h"
@@ -104,6 +105,10 @@ public:
initializeNaryReassociatePass(*PassRegistry::getPassRegistry());
}
+ bool doInitialization(Module &M) override {
+ DL = &M.getDataLayout();
+ return false;
+ }
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
@@ -113,6 +118,7 @@ public:
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<ScalarEvolution>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
AU.setPreservesCFG();
}
@@ -120,16 +126,49 @@ private:
// Runs only one iteration of the dominator-based algorithm. See the header
// comments for why we need multiple iterations.
bool doOneIteration(Function &F);
- // Reasssociates I to a better form.
- Instruction *tryReassociateAdd(Instruction *I);
+
+ // Reassociates I for better CSE.
+ Instruction *tryReassociate(Instruction *I);
+
+ // Reassociate GEP for better CSE.
+ Instruction *tryReassociateGEP(GetElementPtrInst *GEP);
+ // Try splitting GEP at the I-th index and see whether either part can be
+ // CSE'ed. This is a helper function for tryReassociateGEP.
+ //
+ // \p IndexedType The element type indexed by GEP's I-th index. This is
+ // equivalent to
+ // GEP->getIndexedType(GEP->getPointerOperand(), 0-th index,
+ // ..., i-th index).
+ GetElementPtrInst *tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
+ unsigned I, Type *IndexedType);
+ // Given GEP's I-th index = LHS + RHS, see whether &Base[..][LHS][..] or
+ // &Base[..][RHS][..] can be CSE'ed and rewrite GEP accordingly.
+ GetElementPtrInst *tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
+ 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);
+ // Returns the closest dominator of \c Dominatee that computes
+ // \c CandidateExpr. Returns null if not found.
+ Instruction *findClosestMatchingDominator(const SCEV *CandidateExpr,
+ Instruction *Dominatee);
+ // GetElementPtrInst implicitly sign-extends an index if the index is shorter
+ // than the pointer size. This function returns whether Index is shorter than
+ // GEP's pointer size, i.e., whether Index needs to be sign-extended in order
+ // to be an index of GEP.
+ bool requiresSignExtension(Value *Index, GetElementPtrInst *GEP);
+
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
@@ -149,6 +188,7 @@ INITIALIZE_PASS_BEGIN(NaryReassociate, "
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(NaryReassociate, "nary-reassociate", "Nary reassociation",
false, false)
@@ -163,6 +203,7 @@ bool NaryReassociate::runOnFunction(Func
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
SE = &getAnalysis<ScalarEvolution>();
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+ TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
bool Changed = false, ChangedInThisIteration;
do {
@@ -172,26 +213,36 @@ bool NaryReassociate::runOnFunction(Func
return Changed;
}
+// Whitelist the instruction types NaryReassociate handles for now.
+static bool isPotentiallyNaryReassociable(Instruction *I) {
+ switch (I->getOpcode()) {
+ case Instruction::Add:
+ case Instruction::GetElementPtr:
+ return true;
+ default:
+ return false;
+ }
+}
+
bool NaryReassociate::doOneIteration(Function &F) {
bool Changed = false;
SeenExprs.clear();
- // Traverse the dominator tree in the depth-first order. This order makes sure
- // all bases of a candidate are in Candidates when we process it.
+ // Process the basic blocks in pre-order of the dominator tree. This order
+ // ensures that all bases of a candidate are in Candidates when we process it.
for (auto Node = GraphTraits<DominatorTree *>::nodes_begin(DT);
Node != GraphTraits<DominatorTree *>::nodes_end(DT); ++Node) {
BasicBlock *BB = Node->getBlock();
for (auto I = BB->begin(); I != BB->end(); ++I) {
- // Skip vector types which are not SCEVable.
- if (I->getOpcode() == Instruction::Add && !I->getType()->isVectorTy()) {
- if (Instruction *NewI = tryReassociateAdd(I)) {
+ if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(I)) {
+ if (Instruction *NewI = tryReassociate(I)) {
Changed = true;
SE->forgetValue(I);
I->replaceAllUsesWith(NewI);
RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
I = NewI;
}
- // We should add the rewritten instruction because tryReassociateAdd may
- // have invalidated the original one.
+ // Add the rewritten instruction to SeenExprs; the original instruction
+ // is deleted.
SeenExprs[SE->getSCEV(I)].push_back(I);
}
}
@@ -199,7 +250,168 @@ bool NaryReassociate::doOneIteration(Fun
return Changed;
}
-Instruction *NaryReassociate::tryReassociateAdd(Instruction *I) {
+Instruction *NaryReassociate::tryReassociate(Instruction *I) {
+ switch (I->getOpcode()) {
+ case Instruction::Add:
+ return tryReassociateAdd(cast<BinaryOperator>(I));
+ case Instruction::GetElementPtr:
+ return tryReassociateGEP(cast<GetElementPtrInst>(I));
+ default:
+ llvm_unreachable("should be filtered out by isPotentiallyNaryReassociable");
+ }
+}
+
+// FIXME: extract this method into TTI->getGEPCost.
+static bool isGEPFoldable(GetElementPtrInst *GEP,
+ const TargetTransformInfo *TTI,
+ const DataLayout *DL) {
+ GlobalVariable *BaseGV = nullptr;
+ int64_t BaseOffset = 0;
+ bool HasBaseReg = false;
+ int64_t Scale = 0;
+
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getPointerOperand()))
+ BaseGV = GV;
+ else
+ HasBaseReg = true;
+
+ gep_type_iterator GTI = gep_type_begin(GEP);
+ for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I, ++GTI) {
+ if (isa<SequentialType>(*GTI)) {
+ int64_t ElementSize = DL->getTypeAllocSize(GTI.getIndexedType());
+ if (ConstantInt *ConstIdx = dyn_cast<ConstantInt>(*I)) {
+ BaseOffset += ConstIdx->getSExtValue() * ElementSize;
+ } else {
+ // Needs scale register.
+ if (Scale != 0) {
+ // No addressing mode takes two scale registers.
+ return false;
+ }
+ Scale = ElementSize;
+ }
+ } else {
+ StructType *STy = cast<StructType>(*GTI);
+ uint64_t Field = cast<ConstantInt>(*I)->getZExtValue();
+ BaseOffset += DL->getStructLayout(STy)->getElementOffset(Field);
+ }
+ }
+ return TTI->isLegalAddressingMode(GEP->getType()->getElementType(), BaseGV,
+ BaseOffset, HasBaseReg, Scale);
+}
+
+Instruction *NaryReassociate::tryReassociateGEP(GetElementPtrInst *GEP) {
+ // Not worth reassociating GEP if it is foldable.
+ if (isGEPFoldable(GEP, TTI, DL))
+ return nullptr;
+
+ gep_type_iterator GTI = gep_type_begin(*GEP);
+ for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I) {
+ if (isa<SequentialType>(*GTI++)) {
+ if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I - 1, *GTI)) {
+ return NewGEP;
+ }
+ }
+ }
+ return nullptr;
+}
+
+bool NaryReassociate::requiresSignExtension(Value *Index,
+ GetElementPtrInst *GEP) {
+ unsigned PointerSizeInBits =
+ DL->getPointerSizeInBits(GEP->getType()->getPointerAddressSpace());
+ return cast<IntegerType>(Index->getType())->getBitWidth() < PointerSizeInBits;
+}
+
+GetElementPtrInst *
+NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
+ Type *IndexedType) {
+ Value *IndexToSplit = GEP->getOperand(I + 1);
+ if (SExtInst *SExt = dyn_cast<SExtInst>(IndexToSplit))
+ IndexToSplit = SExt->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())
+ return nullptr;
+ Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
+ // IndexToSplit = LHS + RHS.
+ if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I, LHS, RHS, IndexedType))
+ return NewGEP;
+ // Symmetrically, try IndexToSplit = RHS + LHS.
+ if (LHS != RHS) {
+ if (auto *NewGEP =
+ tryReassociateGEPAtIndex(GEP, I, RHS, LHS, IndexedType))
+ return NewGEP;
+ }
+ }
+ return nullptr;
+}
+
+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;
+ for (auto Index = GEP->idx_begin(); Index != GEP->idx_end(); ++Index)
+ IndexExprs.push_back(SE->getSCEV(*Index));
+ // Replace the I-th index with LHS.
+ IndexExprs[I] = SE->getSCEV(LHS);
+ const SCEV *CandidateExpr = SE->getGEPExpr(
+ GEP->getSourceElementType(), SE->getSCEV(GEP->getPointerOperand()),
+ IndexExprs, GEP->isInBounds());
+
+ auto *Candidate = findClosestMatchingDominator(CandidateExpr, GEP);
+ if (Candidate == nullptr)
+ return nullptr;
+
+ PointerType *TypeOfCandidate = dyn_cast<PointerType>(Candidate->getType());
+ // Pretty rare but theoretically possible when a numeric value happens to
+ // share CandidateExpr.
+ if (TypeOfCandidate == nullptr)
+ return nullptr;
+
+ // NewGEP = (char *)Candidate + RHS * sizeof(IndexedType)
+ uint64_t IndexedSize = DL->getTypeAllocSize(IndexedType);
+ Type *ElementType = TypeOfCandidate->getElementType();
+ uint64_t ElementSize = DL->getTypeAllocSize(ElementType);
+ // Another less rare case: because I is not necessarily the last index of the
+ // GEP, the size of the type at the I-th index (IndexedSize) is not
+ // necessarily divisible by ElementSize. For example,
+ //
+ // #pragma pack(1)
+ // struct S {
+ // int a[3];
+ // int64 b[8];
+ // };
+ // #pragma pack()
+ //
+ // sizeof(S) = 100 is indivisible by sizeof(int64) = 8.
+ //
+ // TODO: bail out on this case for now. We could emit uglygep.
+ if (IndexedSize % ElementSize != 0)
+ return nullptr;
+
+ // NewGEP = &Candidate[RHS * (sizeof(IndexedType) / sizeof(Candidate[0])));
+ IRBuilder<> Builder(GEP);
+ Type *IntPtrTy = DL->getIntPtrType(TypeOfCandidate);
+ if (RHS->getType() != IntPtrTy)
+ RHS = Builder.CreateSExtOrTrunc(RHS, IntPtrTy);
+ if (IndexedSize != ElementSize) {
+ RHS = Builder.CreateMul(
+ RHS, ConstantInt::get(IntPtrTy, IndexedSize / ElementSize));
+ }
+ GetElementPtrInst *NewGEP =
+ cast<GetElementPtrInst>(Builder.CreateGEP(Candidate, RHS));
+ NewGEP->setIsInBounds(GEP->isInBounds());
+ NewGEP->takeName(GEP);
+ return NewGEP;
+}
+
+Instruction *NaryReassociate::tryReassociateAdd(BinaryOperator *I) {
Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
if (auto *NewI = tryReassociateAdd(LHS, RHS, I))
return NewI;
@@ -236,22 +448,34 @@ Instruction *NaryReassociate::tryReassoc
if (Pos == SeenExprs.end())
return nullptr;
- auto &LHSCandidates = Pos->second;
// Look for the closest dominator LHS of I that computes LHSExpr, and replace
// I with LHS + RHS.
- //
- // Because we traverse the dominator tree in the pre-order, a
+ auto *LHS = findClosestMatchingDominator(LHSExpr, I);
+ if (LHS == nullptr)
+ return nullptr;
+
+ Instruction *NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
+ NewI->takeName(I);
+ return NewI;
+}
+
+Instruction *
+NaryReassociate::findClosestMatchingDominator(const SCEV *CandidateExpr,
+ Instruction *Dominatee) {
+ auto Pos = SeenExprs.find(CandidateExpr);
+ if (Pos == SeenExprs.end())
+ return nullptr;
+
+ auto &Candidates = Pos->second;
+ // Because we process the basic blocks in pre-order of the dominator tree, a
// candidate that doesn't dominate the current instruction won't dominate any
// future instruction either. Therefore, we pop it out of the stack. This
// optimization makes the algorithm O(n).
- while (!LHSCandidates.empty()) {
- Instruction *LHS = LHSCandidates.back();
- if (DT->dominates(LHS, I)) {
- Instruction *NewI = BinaryOperator::CreateAdd(LHS, RHS, "", I);
- NewI->takeName(I);
- return NewI;
- }
- LHSCandidates.pop_back();
+ while (!Candidates.empty()) {
+ Instruction *Candidate = Candidates.back();
+ if (DT->dominates(Candidate, Dominatee))
+ return Candidate;
+ Candidates.pop_back();
}
return nullptr;
}
Added: llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll?rev=237971&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll (added)
+++ llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll Thu May 21 18:17:30 2015
@@ -0,0 +1,77 @@
+; RUN: opt < %s -nary-reassociate -S | FileCheck %s
+
+target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
+target triple = "nvptx64-unknown-unknown"
+
+declare void @foo(float*)
+
+; foo(&a[i]);
+; foo(&a[i + j]);
+; =>
+; t = &a[i];
+; foo(t);
+; foo(t + j);
+define void @reassociate_gep(float* %a, i64 %i, i64 %j) {
+; CHECK-LABEL: @reassociate_gep(
+ %1 = add i64 %i, %j
+ %2 = getelementptr float, float* %a, i64 %i
+; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i64 %i
+ call void @foo(float* %2)
+; CHECK: call void @foo(float* [[t1]])
+ %3 = getelementptr float, float* %a, i64 %1
+; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 %j
+ call void @foo(float* %3)
+; CHECK: call void @foo(float* [[t2]])
+ ret void
+}
+
+; foo(&a[sext(j)]);
+; foo(&a[sext(i +nsw j)]);
+; =>
+; t = &a[sext(j)];
+; foo(t);
+; foo(t + sext(i));
+define void @reassociate_gep_nsw(float* %a, i32 %i, i32 %j) {
+; CHECK-LABEL: @reassociate_gep_nsw(
+ %1 = add nsw i32 %i, %j
+ %idxprom.1 = sext i32 %1 to i64
+ %idxprom.j = sext i32 %j to i64
+ %2 = getelementptr float, float* %a, i64 %idxprom.j
+; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i64 %idxprom.j
+ call void @foo(float* %2)
+; CHECK: call void @foo(float* [[t1]])
+ %3 = getelementptr float, float* %a, i64 %idxprom.1
+; CHECK: [[sexti:[^ ]+]] = sext i32 %i to i64
+; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 [[sexti]]
+ call void @foo(float* %3)
+; CHECK: call void @foo(float* [[t2]])
+ ret void
+}
+
+; Do not split the second GEP because sext(i + j) != sext(i) + sext(j).
+define void @reassociate_gep_no_nsw(float* %a, i32 %i, i32 %j) {
+; CHECK-LABEL: @reassociate_gep_no_nsw(
+ %1 = add i32 %i, %j
+ %2 = getelementptr float, float* %a, i32 %j
+; CHECK: getelementptr float, float* %a, i32 %j
+ call void @foo(float* %2)
+ %3 = getelementptr float, float* %a, i32 %1
+; CHECK: getelementptr float, float* %a, i32 %1
+ call void @foo(float* %3)
+ ret void
+}
+
+define void @reassociate_gep_128(float* %a, i128 %i, i128 %j) {
+; CHECK-LABEL: @reassociate_gep_128(
+ %1 = add i128 %i, %j
+ %2 = getelementptr float, float* %a, i128 %i
+; CHECK: [[t1:[^ ]+]] = getelementptr float, float* %a, i128 %i
+ call void @foo(float* %2)
+; CHECK: call void @foo(float* [[t1]])
+ %3 = getelementptr float, float* %a, i128 %1
+; CHECK: [[truncj:[^ ]+]] = trunc i128 %j to i64
+; CHECK: [[t2:[^ ]+]] = getelementptr float, float* [[t1]], i64 [[truncj]]
+ call void @foo(float* %3)
+; CHECK: call void @foo(float* [[t2]])
+ ret void
+}
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