[llvm] r241139 - [NaryReassociate] enhances nsw by leveraging @llvm.assume
Jingyue Wu
jingyue at google.com
Tue Jun 30 20:38:50 PDT 2015
Author: jingyue
Date: Tue Jun 30 22:38:49 2015
New Revision: 241139
URL: http://llvm.org/viewvc/llvm-project?rev=241139&view=rev
Log:
[NaryReassociate] enhances nsw by leveraging @llvm.assume
Summary:
nsw are flaky and can often be removed by optimizations. This patch enhances
nsw by leveraging @llvm.assume in the IR. Specifically, NaryReassociate now
understands that
assume(a + b >= 0) && assume(a >= 0) ==> a +nsw b
As a result, it can split more sext(a + b) into sext(a) + sext(b) for CSE.
Test Plan: nary-gep.ll
Reviewers: broune, meheff
Subscribers: jholewinski, llvm-commits
Differential Revision: http://reviews.llvm.org/D10822
Modified:
llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll
Modified: llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp?rev=241139&r1=241138&r2=241139&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp Tue Jun 30 22:38:49 2015
@@ -74,21 +74,18 @@
// 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.
-//
//===----------------------------------------------------------------------===//
+#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;
@@ -115,6 +112,7 @@ public:
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<ScalarEvolution>();
AU.addPreserved<TargetLibraryInfoWrapperPass>();
+ AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<ScalarEvolution>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
@@ -163,12 +161,18 @@ private:
// 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);
+ // Returns whether V is known to be non-negative at context \c Ctxt.
+ bool isKnownNonNegative(Value *V, Instruction *Ctxt);
+ // Returns whether AO may sign overflow at context \c Ctxt. It computes a
+ // conservative result -- it answers true when not sure.
+ bool maySignOverflow(AddOperator *AO, Instruction *Ctxt);
+ 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
@@ -185,6 +189,7 @@ private:
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(TargetLibraryInfoWrapperPass)
@@ -200,6 +205,7 @@ bool NaryReassociate::runOnFunction(Func
if (skipOptnoneFunction(F))
return false;
+ AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
SE = &getAnalysis<ScalarEvolution>();
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
@@ -346,18 +352,44 @@ bool NaryReassociate::requiresSignExtens
return cast<IntegerType>(Index->getType())->getBitWidth() < PointerSizeInBits;
}
+bool NaryReassociate::isKnownNonNegative(Value *V, Instruction *Ctxt) {
+ bool NonNegative, Negative;
+ // TODO: ComputeSignBits is expensive. Consider caching the results.
+ ComputeSignBit(V, NonNegative, Negative, *DL, 0, AC, Ctxt, DT);
+ return NonNegative;
+}
+
+bool NaryReassociate::maySignOverflow(AddOperator *AO, Instruction *Ctxt) {
+ if (AO->hasNoSignedWrap())
+ return false;
+
+ Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
+ // If LHS or RHS has the same sign as the sum, AO doesn't sign overflow.
+ // TODO: handle the negative case as well.
+ if (isKnownNonNegative(AO, Ctxt) &&
+ (isKnownNonNegative(LHS, Ctxt) || isKnownNonNegative(RHS, Ctxt)))
+ return false;
+
+ return true;
+}
+
GetElementPtrInst *
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), GEP))
+ 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) && maySignOverflow(AO, GEP))
return nullptr;
Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
// IndexToSplit = LHS + RHS.
@@ -373,10 +405,9 @@ NaryReassociate::tryReassociateGEPAtInde
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;
@@ -384,6 +415,16 @@ NaryReassociate::tryReassociateGEPAtInde
IndexExprs.push_back(SE->getSCEV(*Index));
// Replace the I-th index with LHS.
IndexExprs[I] = SE->getSCEV(LHS);
+ if (isKnownNonNegative(LHS, GEP) &&
+ 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());
Modified: 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=241139&r1=241138&r2=241139&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll (original)
+++ llvm/trunk/test/Transforms/NaryReassociate/NVPTX/nary-gep.ll Tue Jun 30 22:38:49 2015
@@ -61,6 +61,40 @@ define void @reassociate_gep_nsw(float*
ret void
}
+; assume(j >= 0);
+; foo(&a[zext(j)]);
+; assume(i + j >= 0);
+; foo(&a[zext(i + j)]);
+; =>
+; t1 = &a[zext(j)];
+; foo(t1);
+; t2 = t1 + sext(i);
+; foo(t2);
+define void @reassociate_gep_assume(float* %a, i32 %i, i32 %j) {
+; CHECK-LABEL: @reassociate_gep_assume(
+ ; assume(j >= 0)
+ %cmp = icmp sgt i32 %j, -1
+ call void @llvm.assume(i1 %cmp)
+ %1 = add i32 %i, %j
+ %cmp2 = icmp sgt i32 %1, -1
+ call void @llvm.assume(i1 %cmp2)
+
+ %idxprom.j = zext 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]])
+
+ %idxprom.1 = zext i32 %1 to i64
+ %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(
@@ -88,3 +122,5 @@ define void @reassociate_gep_128(float*
; CHECK: call void @foo(float* [[t2]])
ret void
}
+
+declare void @llvm.assume(i1)
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