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Make this transformation slightly less agressive and more correct. 

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
View File

@ -1609,23 +1609,33 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
if (llvm::isKnownNonNull(LHSPtr) || llvm::isKnownNonNull(RHSPtr)) { if (llvm::isKnownNonNull(LHSPtr) || llvm::isKnownNonNull(RHSPtr)) {
// If both sides are different identified objects, they aren't equal // If both sides are different identified objects, they aren't equal
// unless they're null. // unless they're null.
if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr)) if (LHSPtr != RHSPtr && llvm::isIdentifiedObject(RHSPtr) &&
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred)); (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 // A local identified object (alloca or noalias call) can't equal any
// incoming argument, unless they're both null. // incoming argument, unless they're both null.
if (isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr)) if (isa<Instruction>(LHSPtr) && isa<Argument>(RHSPtr) &&
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred)); (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::FCMP_UEQ))
return ConstantInt::get(ITy, false);
} }
// Assume that the constant null is on the right. // Assume that the constant null is on the right.
if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr)) if (llvm::isKnownNonNull(LHSPtr) && isa<ConstantPointerNull>(RHSPtr)) {
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred)); 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)) { } else if (isa<Argument>(LHSPtr)) {
RHSPtr = RHSPtr->stripInBoundsOffsets(); RHSPtr = RHSPtr->stripInBoundsOffsets();
// An alloca can't be equal to an argument. // An alloca can't be equal to an argument.
if (isa<AllocaInst>(RHSPtr)) if (isa<AllocaInst>(RHSPtr)) {
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred)); 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. // If we are comparing with zero then try hard since this is a common case.

35
llvm/test/Transforms/InstCombine/2012-03-10-InstCombine.ll Normal file
View File

@ -0,0 +1,35 @@
; RUN: opt < %s -instcombine | FileCheck %s
; Derived from gcc.c-torture/execute/frame-address.c
; CHECK: @func
; CHECK: return:
; CHECK-NOT: ret i32 0
; CHECK: ret i32 %retval
define i32 @func(i8* %c, i8* %f) nounwind uwtable readnone noinline ssp {
entry:
%d = alloca i8, align 1
store i8 0, i8* %d, align 1
%cmp = icmp ugt i8* %d, %c
br i1 %cmp, label %if.else, label %if.then
if.then: ; preds = %entry
%cmp2 = icmp ule i8* %d, %f
%not.cmp1 = icmp uge i8* %c, %f
%.cmp2 = and i1 %cmp2, %not.cmp1
%land.ext = zext i1 %.cmp2 to i32
br label %return
if.else: ; preds = %entry
%cmp5 = icmp uge i8* %d, %f
%not.cmp3 = icmp ule i8* %c, %f
%.cmp5 = and i1 %cmp5, %not.cmp3
%land.ext7 = zext i1 %.cmp5 to i32
br label %return
return: ; preds = %if.else, %if.then
%retval.0 = phi i32 [ %land.ext, %if.then ], [ %land.ext7, %if.else ]
ret i32 %retval.0
}