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Teach BasicAA how to analyze Select instructions, and make it more
aggressive on PHI instructions. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85158 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
parent
cadd4b9ced
commit
6665b0ea68
@ -217,7 +217,7 @@ namespace {
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private:
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// VisitedPHIs - Track PHI nodes visited by a aliasCheck() call.
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SmallPtrSet<const PHINode*, 16> VisitedPHIs;
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SmallPtrSet<const Value*, 16> VisitedPHIs;
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// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
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// against another.
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@ -229,6 +229,10 @@ namespace {
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AliasResult aliasPHI(const PHINode *PN, unsigned PNSize,
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const Value *V2, unsigned V2Size);
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/// aliasSelect - Disambiguate a Select instruction against another value.
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AliasResult aliasSelect(const SelectInst *SI, unsigned SISize,
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const Value *V2, unsigned V2Size);
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AliasResult aliasCheck(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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@ -519,6 +523,41 @@ BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
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return MayAlias;
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}
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// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select instruction
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// against another.
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AliasAnalysis::AliasResult
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BasicAliasAnalysis::aliasSelect(const SelectInst *SI, unsigned SISize,
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const Value *V2, unsigned V2Size) {
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// If the values are Selects with the same condition, we can do a more precise
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// check: just check for aliases between the values on corresponding arms.
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if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
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if (SI->getCondition() == SI2->getCondition()) {
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AliasResult Alias =
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aliasCheck(SI->getTrueValue(), SISize,
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SI2->getTrueValue(), V2Size);
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if (Alias == MayAlias)
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return MayAlias;
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AliasResult ThisAlias =
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aliasCheck(SI->getFalseValue(), SISize,
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SI2->getFalseValue(), V2Size);
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if (ThisAlias != Alias)
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return MayAlias;
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return Alias;
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}
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// If both arms of the Select node NoAlias or MustAlias V2, then returns
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// NoAlias / MustAlias. Otherwise, returns MayAlias.
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AliasResult Alias =
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aliasCheck(SI->getTrueValue(), SISize, V2, V2Size);
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if (Alias == MayAlias)
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return MayAlias;
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AliasResult ThisAlias =
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aliasCheck(SI->getFalseValue(), SISize, V2, V2Size);
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if (ThisAlias != Alias)
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return MayAlias;
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return Alias;
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}
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// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
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// against another.
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AliasAnalysis::AliasResult
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@ -528,6 +567,28 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
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if (!VisitedPHIs.insert(PN))
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return MayAlias;
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// If the values are PHIs in the same block, we can do a more precise
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// as well as efficient check: just check for aliases between the values
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// on corresponding edges.
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if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
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if (PN2->getParent() == PN->getParent()) {
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AliasResult Alias =
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aliasCheck(PN->getIncomingValue(0), PNSize,
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PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
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V2Size);
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if (Alias == MayAlias)
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return MayAlias;
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for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
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AliasResult ThisAlias =
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aliasCheck(PN->getIncomingValue(i), PNSize,
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PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
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V2Size);
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if (ThisAlias != Alias)
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return MayAlias;
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}
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return Alias;
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}
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SmallPtrSet<Value*, 4> UniqueSrc;
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SmallVector<Value*, 4> V1Srcs;
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
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@ -542,7 +603,7 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
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V1Srcs.push_back(PV1);
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}
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AliasResult Alias = aliasCheck(V1Srcs[0], PNSize, V2, V2Size);
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AliasResult Alias = aliasCheck(V2, V2Size, V1Srcs[0], PNSize);
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// Early exit if the check of the first PHI source against V2 is MayAlias.
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// Other results are not possible.
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if (Alias == MayAlias)
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@ -552,6 +613,12 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
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// NoAlias / MustAlias. Otherwise, returns MayAlias.
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for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
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Value *V = V1Srcs[i];
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// If V2 is a PHI, the recursive case will have been caught in the
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// above aliasCheck call, so these subsequent calls to aliasCheck
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// don't need to assume that V2 is being visited recursively.
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VisitedPHIs.erase(V2);
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AliasResult ThisAlias = aliasCheck(V2, V2Size, V, PNSize);
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if (ThisAlias != Alias || ThisAlias == MayAlias)
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return MayAlias;
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@ -628,6 +695,13 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
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if (const PHINode *PN = dyn_cast<PHINode>(V1))
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return aliasPHI(PN, V1Size, V2, V2Size);
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if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
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std::swap(V1, V2);
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std::swap(V1Size, V2Size);
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}
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if (const SelectInst *S1 = dyn_cast<SelectInst>(V1))
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return aliasSelect(S1, V1Size, V2, V2Size);
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return MayAlias;
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}
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73
test/Analysis/BasicAA/phi-and-select.ll
Normal file
73
test/Analysis/BasicAA/phi-and-select.ll
Normal file
@ -0,0 +1,73 @@
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; RUN: opt < %s -aa-eval -print-all-alias-modref-info -disable-output \
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; RUN: |& grep {NoAlias: double\\* \[%\]a, double\\* \[%\]b\$} | count 4
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; BasicAA should detect NoAliases in PHIs and Selects.
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; Two PHIs in the same block.
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define void @foo(i1 %m, double* noalias %x, double* noalias %y) {
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entry:
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br i1 %m, label %true, label %false
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true:
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br label %exit
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false:
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br label %exit
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exit:
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%a = phi double* [ %x, %true ], [ %y, %false ]
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%b = phi double* [ %x, %false ], [ %y, %true ]
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volatile store double 0.0, double* %a
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volatile store double 1.0, double* %b
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ret void
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}
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; Two selects with the same condition.
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define void @bar(i1 %m, double* noalias %x, double* noalias %y) {
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entry:
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%a = select i1 %m, double* %x, double* %y
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%b = select i1 %m, double* %y, double* %x
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volatile store double 0.000000e+00, double* %a
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volatile store double 1.000000e+00, double* %b
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ret void
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}
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; Two PHIs with disjoint sets of inputs.
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define void @qux(i1 %m, double* noalias %x, double* noalias %y,
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i1 %n, double* noalias %v, double* noalias %w) {
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entry:
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br i1 %m, label %true, label %false
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true:
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br label %exit
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false:
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br label %exit
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exit:
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%a = phi double* [ %x, %true ], [ %y, %false ]
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br i1 %n, label %ntrue, label %nfalse
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ntrue:
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br label %nexit
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nfalse:
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br label %nexit
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nexit:
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%b = phi double* [ %v, %ntrue ], [ %w, %nfalse ]
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volatile store double 0.0, double* %a
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volatile store double 1.0, double* %b
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ret void
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}
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; Two selects with disjoint sets of arms.
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define void @fin(i1 %m, double* noalias %x, double* noalias %y,
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i1 %n, double* noalias %v, double* noalias %w) {
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entry:
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%a = select i1 %m, double* %x, double* %y
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%b = select i1 %n, double* %v, double* %w
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volatile store double 0.000000e+00, double* %a
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volatile store double 1.000000e+00, double* %b
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ret void
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}
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