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Make this transformation slightly less agressive and more correct.

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The 'CmpInst::isFalseWhenEqual' function returns 'false' for values other than
simply equality. For instance, it returns 'false' for <= or >=. This isn't the
correct behavior for this transformation, which is checking for strict equality
and non-equality. It was causing the gcc.c-torture/execute/frame-address.c test
to fail because it would completely (and incorrectly) optimize a whole function
into a 'ret i32 0'.

llvm-svn: 152497
This commit is contained in:
Bill Wendling
2012-03-10 17:56:03 +00:00
parent b52221e941
commit 0624d2a1ec
2 changed files with 53 additions and 8 deletions
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26
llvm/lib/Analysis/InstructionSimplify.cpp
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@@ -1609,23 +1609,33 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
if (llvm::isKnownNonNull(LHSPtr) || llvm::isKnownNonNull(RHSPtr)) {
// If both sides are different identified objects, they aren't equal
// unless they're null.
if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr) &&
(Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ))
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))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
if (isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr) &&
(Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ))
return ConstantInt::get(ITy, false);
}
// Assume that the constant null is on the right.
if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr)) {
if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ)
return ConstantInt::get(ITy, false);
else if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::FCMP_ONE)
return ConstantInt::get(ITy, true);
}
} else if (isa<Argument>(LHSPtr)) {
RHSPtr = RHSPtr->stripInBoundsOffsets();
// An alloca can't be equal to an argument.
if (isa<AllocaInst>(RHSPtr))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
if (isa<AllocaInst>(RHSPtr)) {
if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ)
return ConstantInt::get(ITy, false);
else if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::FCMP_ONE)
return ConstantInt::get(ITy, true);
}
}
// If we are comparing with zero then try hard since this is a common case.