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Fix PR13412, a nasty miscompile due to the interleaved

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instsimplify+inline strategy.

The crux of the problem is that instsimplify was reasonably relying on
an invariant that is true within any single function, but is no longer
true mid-inline the way we use it. This invariant is that an argument
pointer != a local (alloca) pointer.

The fix is really light weight though, and allows instsimplify to be
resiliant to these situations: when checking the relation ships to
function arguments, ensure that the argumets come from the same
function. If they come from different functions, then none of these
assumptions hold. All credit to Benjamin Kramer for coming up with this
clever solution to the problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161410 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth
2012-08-07 10:59:59 +00:00
parent e6450dc2af
commit 961e1acfb2
2 changed files with 79 additions and 11 deletions
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28
lib/Analysis/InstructionSimplify.cpp
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@ -1719,10 +1719,13 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
return ConstantInt::get(ITy, false);
// A local identified object (alloca or noalias call) can't equal any
// incoming argument, unless they're both null.
if (isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr) &&
Pred == CmpInst::ICMP_EQ)
return ConstantInt::get(ITy, false);
// incoming argument, unless they're both null or they belong to
// different functions. The latter happens during inlining.
if (Instruction *LHSInst = dyn_cast<Instruction>(LHSPtr))
if (Argument *RHSArg = dyn_cast<Argument>(RHSPtr))
if (LHSInst->getParent()->getParent() == RHSArg->getParent() &&
Pred == CmpInst::ICMP_EQ)
return ConstantInt::get(ITy, false);
}
// Assume that the constant null is on the right.
@ -1732,14 +1735,17 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
else if (Pred == CmpInst::ICMP_NE)
return ConstantInt::get(ITy, true);
}
} else if (isa<Argument>(LHSPtr)) {
} else if (Argument *LHSArg = dyn_cast<Argument>(LHSPtr)) {
RHSPtr = RHSPtr->stripInBoundsOffsets();
// An alloca can't be equal to an argument.
if (isa<AllocaInst>(RHSPtr)) {
if (Pred == CmpInst::ICMP_EQ)
return ConstantInt::get(ITy, false);
else if (Pred == CmpInst::ICMP_NE)
return ConstantInt::get(ITy, true);
// An alloca can't be equal to an argument unless they come from separate
// functions via inlining.
if (AllocaInst *RHSInst = dyn_cast<AllocaInst>(RHSPtr)) {
if (LHSArg->getParent() == RHSInst->getParent()->getParent()) {
if (Pred == CmpInst::ICMP_EQ)
return ConstantInt::get(ITy, false);
else if (Pred == CmpInst::ICMP_NE)
return ConstantInt::get(ITy, true);
}
}
}