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[DA] Improve alias checking in dependence analysis
Improve the alias analysis to account for cases where we know that src/dst pairs cannot alias due to things like TBAA. As we know they are noalias, we know no dependency can occur. Also fixes issues around the size parameter to AA being incorrect. Differential Revision: https://reviews.llvm.org/D42381 llvm-svn: 329692
This commit is contained in:
David Green
parent
4152237804
commit
5c2971f373
@ -621,13 +621,38 @@ void Dependence::dump(raw_ostream &OS) const {
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OS << "!\n";
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}
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// Returns NoAlias/MayAliass/MustAlias for two memory locations based upon their
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// underlaying objects. If LocA and LocB are known to not alias (for any reason:
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// tbaa, non-overlapping regions etc), then it is known there is no dependecy.
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// Otherwise the underlying objects are checked to see if they point to
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// different identifiable objects.
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static AliasResult underlyingObjectsAlias(AliasAnalysis *AA,
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const DataLayout &DL, const Value *A,
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const Value *B) {
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const Value *AObj = GetUnderlyingObject(A, DL);
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const Value *BObj = GetUnderlyingObject(B, DL);
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return AA->alias(AObj, DL.getTypeStoreSize(AObj->getType()),
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BObj, DL.getTypeStoreSize(BObj->getType()));
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const DataLayout &DL,
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const MemoryLocation &LocA,
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const MemoryLocation &LocB) {
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// Check the original locations (minus size) for noalias, which can happen for
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// tbaa, incompatible underlying object locations, etc.
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MemoryLocation LocAS(LocA.Ptr, MemoryLocation::UnknownSize, LocA.AATags);
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MemoryLocation LocBS(LocB.Ptr, MemoryLocation::UnknownSize, LocB.AATags);
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if (AA->alias(LocAS, LocBS) == NoAlias)
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return NoAlias;
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// Check the underlying objects are the same
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const Value *AObj = GetUnderlyingObject(LocA.Ptr, DL);
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const Value *BObj = GetUnderlyingObject(LocB.Ptr, DL);
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// If the underlying objects are the same, they must alias
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if (AObj == BObj)
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return MustAlias;
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// We may have hit the recursion limit for underlying objects, or have
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// underlying objects where we don't know they will alias.
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if (!isIdentifiedObject(AObj) || !isIdentifiedObject(BObj))
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return MayAlias;
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// Otherwise we know the objects are different and both identified objects so
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// must not alias.
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return NoAlias;
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}
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@ -3298,8 +3323,9 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
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Value *SrcPtr = getLoadStorePointerOperand(Src);
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Value *DstPtr = getLoadStorePointerOperand(Dst);
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switch (underlyingObjectsAlias(AA, F->getParent()->getDataLayout(), DstPtr,
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SrcPtr)) {
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switch (underlyingObjectsAlias(AA, F->getParent()->getDataLayout(),
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MemoryLocation::get(Dst),
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MemoryLocation::get(Src))) {
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case MayAlias:
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case PartialAlias:
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// cannot analyse objects if we don't understand their aliasing.
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@ -3715,8 +3741,9 @@ const SCEV *DependenceInfo::getSplitIteration(const Dependence &Dep,
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assert(isLoadOrStore(Dst));
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Value *SrcPtr = getLoadStorePointerOperand(Src);
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Value *DstPtr = getLoadStorePointerOperand(Dst);
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assert(underlyingObjectsAlias(AA, F->getParent()->getDataLayout(), DstPtr,
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SrcPtr) == MustAlias);
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assert(underlyingObjectsAlias(AA, F->getParent()->getDataLayout(),
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MemoryLocation::get(Dst),
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MemoryLocation::get(Src)) == MustAlias);
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// establish loop nesting levels
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establishNestingLevels(Src, Dst);
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140
test/Analysis/DependenceAnalysis/AA.ll
Normal file
140
test/Analysis/DependenceAnalysis/AA.ll
Normal file
@ -0,0 +1,140 @@
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; RUN: opt < %s -analyze -basicaa -tbaa -da | FileCheck %s
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; CHECK-LABEL: 'Dependence Analysis' for function 'test_no_noalias'
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; CHECK: da analyze - none!
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; CHECK: da analyze - confused!
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; CHECK: da analyze - none!
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define void @test_no_noalias(i32* %A, i32* %B) {
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store i32 1, i32* %A
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store i32 2, i32* %B
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ret void
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}
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; CHECK-LABEL: test_one_noalias
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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define void @test_one_noalias(i32* noalias %A, i32* %B) {
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store i32 1, i32* %A
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store i32 2, i32* %B
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ret void
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}
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; CHECK-LABEL: test_two_noalias
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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define void @test_two_noalias(i32* noalias %A, i32* noalias %B) {
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store i32 1, i32* %A
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store i32 2, i32* %B
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ret void
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}
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; CHECK-LABEL: test_global_alias
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; CHECK: da analyze - none!
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; CHECK: da analyze - confused!
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; CHECK: da analyze - none!
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@g = global i32 5
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define void @test_global_alias(i32* %A) {
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store i32 1, i32* %A
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store i32 2, i32* @g
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ret void
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}
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; CHECK-LABEL: test_global_noalias
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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define void @test_global_noalias(i32* noalias %A) {
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store i32 1, i32* %A
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store i32 2, i32* @g
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ret void
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}
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; CHECK-LABEL: test_global_size
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; CHECK: da analyze - none!
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; CHECK: da analyze - confused!
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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; CHECK: da analyze - confused!
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; CHECK: da analyze - none!
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@a = global i16 5, align 2
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@b = global i16* @a, align 4
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define void @test_global_size() {
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%l0 = load i16*, i16** @b, align 4
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%l1 = load i16, i16* %l0, align 2
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store i16 1, i16* @a, align 2
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ret void
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}
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; CHECK-LABEL: test_tbaa_same
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; CHECK: da analyze - none!
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; CHECK: da analyze - confused!
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; CHECK: da analyze - none!
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define void @test_tbaa_same(i32* %A, i32* %B) {
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store i32 1, i32* %A, !tbaa !5
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store i32 2, i32* %B, !tbaa !5
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ret void
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}
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; CHECK-LABEL: test_tbaa_diff
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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; CHECK: da analyze - none!
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define void @test_tbaa_diff(i32* %A, i16* %B) {
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store i32 1, i32* %A, !tbaa !5
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store i16 2, i16* %B, !tbaa !9
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ret void
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}
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; CHECK-LABEL: tbaa_loop
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; CHECK: da analyze - input
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; CHECK: da analyze - none
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; CHECK: da analyze - output
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define void @tbaa_loop(i32 %I, i32 %J, i32* nocapture %A, i16* nocapture readonly %B) {
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entry:
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%cmp = icmp ne i32 %J, 0
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%cmp122 = icmp ne i32 %I, 0
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%or.cond = and i1 %cmp, %cmp122
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br i1 %or.cond, label %for.outer.preheader, label %for.end
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for.outer.preheader:
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br label %for.outer
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for.outer:
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%i.us = phi i32 [ %add8.us, %for.latch ], [ 0, %for.outer.preheader ]
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br label %for.inner
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for.inner:
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%j.us = phi i32 [ 0, %for.outer ], [ %inc.us, %for.inner ]
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%sum1.us = phi i32 [ 0, %for.outer ], [ %add.us, %for.inner ]
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%arrayidx.us = getelementptr inbounds i16, i16* %B, i32 %j.us
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%0 = load i16, i16* %arrayidx.us, align 4, !tbaa !9
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%sext = sext i16 %0 to i32
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%add.us = add i32 %sext, %sum1.us
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%inc.us = add nuw i32 %j.us, 1
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%exitcond = icmp eq i32 %inc.us, %J
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br i1 %exitcond, label %for.latch, label %for.inner
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for.latch:
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%add.us.lcssa = phi i32 [ %add.us, %for.inner ]
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%arrayidx6.us = getelementptr inbounds i32, i32* %A, i32 %i.us
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store i32 %add.us.lcssa, i32* %arrayidx6.us, align 4, !tbaa !5
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%add8.us = add nuw i32 %i.us, 1
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%exitcond25 = icmp eq i32 %add8.us, %I
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br i1 %exitcond25, label %for.end.loopexit, label %for.outer
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for.end.loopexit:
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br label %for.end
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for.end:
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ret void
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}
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!5 = !{!6, !6, i64 0}
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!6 = !{!"int", !7, i64 0}
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!7 = !{!"omnipotent char", !8, i64 0}
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!8 = !{!"Simple C/C++ TBAA"}
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!9 = !{!10, !10, i64 0}
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!10 = !{!"short", !7, i64 0}
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