[llvm-commits] [llvm] r107071 - in /llvm/trunk: lib/Analysis/BasicAliasAnalysis.cpp lib/VMCore/Value.cpp test/Analysis/BasicAA/unreachable-block.ll
Dan Gohman
gohman at apple.com
Mon Jun 28 14:16:52 PDT 2010
Author: djg
Date: Mon Jun 28 16:16:52 2010
New Revision: 107071
URL: http://llvm.org/viewvc/llvm-project?rev=107071&view=rev
Log:
Fix Value::stripPointerCasts and BasicAA to avoid trouble on
code in unreachable blocks, which have have use-def cycles.
This fixes PR7514.
Added:
llvm/trunk/test/Analysis/BasicAA/unreachable-block.ll
Modified:
llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
llvm/trunk/lib/VMCore/Value.cpp
Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=107071&r1=107070&r2=107071&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Mon Jun 28 16:16:52 2010
@@ -189,9 +189,9 @@
BasicAliasAnalysis() : NoAA(&ID) {}
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
- assert(VisitedPHIs.empty() && "VisitedPHIs must be cleared after use!");
+ assert(Visited.empty() && "Visited must be cleared after use!");
AliasResult Alias = aliasCheck(V1, V1Size, V2, V2Size);
- VisitedPHIs.clear();
+ Visited.clear();
return Alias;
}
@@ -213,8 +213,8 @@
}
private:
- // VisitedPHIs - Track PHI nodes visited by a aliasCheck() call.
- SmallPtrSet<const Value*, 16> VisitedPHIs;
+ // Visited - Track instructions visited by a aliasPHI, aliasSelect(), and aliasGEP().
+ SmallPtrSet<const Value*, 16> Visited;
// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
// instruction against another.
@@ -440,6 +440,13 @@
const Value *V2, unsigned V2Size,
const Value *UnderlyingV1,
const Value *UnderlyingV2) {
+ // If this GEP has been visited before, we're on a use-def cycle.
+ // Such cycles are only valid when PHI nodes are involved or in unreachable
+ // code. The visitPHI function catches cycles containing PHIs, but there
+ // could still be a cycle without PHIs in unreachable code.
+ if (!Visited.insert(GEP1))
+ return MayAlias;
+
int64_t GEP1BaseOffset;
SmallVector<std::pair<const Value*, int64_t>, 4> GEP1VariableIndices;
@@ -550,6 +557,13 @@
AliasAnalysis::AliasResult
BasicAliasAnalysis::aliasSelect(const SelectInst *SI, unsigned SISize,
const Value *V2, unsigned V2Size) {
+ // If this select has been visited before, we're on a use-def cycle.
+ // Such cycles are only valid when PHI nodes are involved or in unreachable
+ // code. The visitPHI function catches cycles containing PHIs, but there
+ // could still be a cycle without PHIs in unreachable code.
+ if (!Visited.insert(SI))
+ return MayAlias;
+
// If the values are Selects with the same condition, we can do a more precise
// check: just check for aliases between the values on corresponding arms.
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
@@ -570,11 +584,17 @@
// If both arms of the Select node NoAlias or MustAlias V2, then returns
// NoAlias / MustAlias. Otherwise, returns MayAlias.
AliasResult Alias =
- aliasCheck(SI->getTrueValue(), SISize, V2, V2Size);
+ aliasCheck(V2, V2Size, SI->getTrueValue(), SISize);
if (Alias == MayAlias)
return MayAlias;
+
+ // If V2 is visited, the recursive case will have been caught in the
+ // above aliasCheck call, so these subsequent calls to aliasCheck
+ // don't need to assume that V2 is being visited recursively.
+ Visited.erase(V2);
+
AliasResult ThisAlias =
- aliasCheck(SI->getFalseValue(), SISize, V2, V2Size);
+ aliasCheck(V2, V2Size, SI->getFalseValue(), SISize);
if (ThisAlias != Alias)
return MayAlias;
return Alias;
@@ -586,7 +606,7 @@
BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
const Value *V2, unsigned V2Size) {
// The PHI node has already been visited, avoid recursion any further.
- if (!VisitedPHIs.insert(PN))
+ if (!Visited.insert(PN))
return MayAlias;
// If the values are PHIs in the same block, we can do a more precise
@@ -636,10 +656,10 @@
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
Value *V = V1Srcs[i];
- // If V2 is a PHI, the recursive case will have been caught in the
+ // If V2 is visited, the recursive case will have been caught in the
// above aliasCheck call, so these subsequent calls to aliasCheck
// don't need to assume that V2 is being visited recursively.
- VisitedPHIs.erase(V2);
+ Visited.erase(V2);
AliasResult ThisAlias = aliasCheck(V2, V2Size, V, PNSize);
if (ThisAlias != Alias || ThisAlias == MayAlias)
Modified: llvm/trunk/lib/VMCore/Value.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/VMCore/Value.cpp?rev=107071&r1=107070&r2=107071&view=diff
==============================================================================
--- llvm/trunk/lib/VMCore/Value.cpp (original)
+++ llvm/trunk/lib/VMCore/Value.cpp Mon Jun 28 16:16:52 2010
@@ -322,7 +322,13 @@
Value *Value::stripPointerCasts() {
if (!getType()->isPointerTy())
return this;
+
+ // Even though we don't look through PHI nodes, we could be called on an
+ // instruction in an unreachable block, which may be on a cycle.
+ SmallPtrSet<Value *, 4> Visited;
+
Value *V = this;
+ Visited.insert(V);
do {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
if (!GEP->hasAllZeroIndices())
@@ -338,7 +344,9 @@
return V;
}
assert(V->getType()->isPointerTy() && "Unexpected operand type!");
- } while (1);
+ } while (Visited.insert(V));
+
+ return V;
}
Value *Value::getUnderlyingObject(unsigned MaxLookup) {
Added: llvm/trunk/test/Analysis/BasicAA/unreachable-block.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/unreachable-block.ll?rev=107071&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/BasicAA/unreachable-block.ll (added)
+++ llvm/trunk/test/Analysis/BasicAA/unreachable-block.ll Mon Jun 28 16:16:52 2010
@@ -0,0 +1,16 @@
+; RUN: opt -aa-eval -disable-output < %s >& /dev/null
+
+; BasicAA shouldn't infinitely recurse on the use-def cycles in
+; unreachable code.
+
+define void @func_2() nounwind {
+entry:
+ unreachable
+
+bb:
+ %t = select i1 undef, i32* %t, i32* undef
+ %p = select i1 undef, i32* %p, i32* %p
+ %q = select i1 undef, i32* undef, i32* %p
+ %a = getelementptr i8* %a, i32 0
+ unreachable
+}
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