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InstCombine: Fix infinite loop caused by visitFPTrunc

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We would attempt to replace a fptrunc of an frem with an identical
fptrunc.  This would cause the new fptrunc to be added to the worklist.
Of course, this results in an infinite loop because we will keep
visiting the newly created fptruncs.

This fixes PR21576.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222040 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-11-14 21:21:15 +00:00
parent 1523db7c64
commit 9019a6092d
2 changed files with 19 additions and 6 deletions
lib/Transforms/InstCombine
InstCombineCasts.cpp
test/Transforms/InstCombine
fpcast.ll

15
lib/Transforms/InstCombine/InstCombineCasts.cpp

@ -1269,14 +1269,17 @@ Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) {
// type of OpI doesn't enter into things at all. We simply evaluate
// in whichever source type is larger, then convert to the
// destination type.
Value *NewLHS = LHSOrig, *NewRHS = RHSOrig;
if (LHSWidth < SrcWidth)
LHSOrig = Builder->CreateFPExt(LHSOrig, RHSOrig->getType());
NewLHS = Builder->CreateFPExt(NewLHS, RHSOrig->getType());
else if (RHSWidth <= SrcWidth)
RHSOrig = Builder->CreateFPExt(RHSOrig, LHSOrig->getType());
Value *ExactResult = Builder->CreateFRem(LHSOrig, RHSOrig);
if (Instruction *RI = dyn_cast<Instruction>(ExactResult))
RI->copyFastMathFlags(OpI);
return CastInst::CreateFPCast(ExactResult, CI.getType());
NewRHS = Builder->CreateFPExt(NewRHS, LHSOrig->getType());
if (NewLHS != LHSOrig || NewRHS != RHSOrig) {
Value *ExactResult = Builder->CreateFRem(NewLHS, NewRHS);
if (Instruction *RI = dyn_cast<Instruction>(ExactResult))
RI->copyFastMathFlags(OpI);
return CastInst::CreateFPCast(ExactResult, CI.getType());
}
}
// (fptrunc (fneg x)) -> (fneg (fptrunc x))

10
test/Transforms/InstCombine/fpcast.ll

@ -53,3 +53,13 @@ define half @test5(float %a, float %b, float %c) {
}
declare float @llvm.fabs.f32(float) nounwind readonly
define <1 x float> @test6(<1 x double> %V) {
%frem = frem <1 x double> %V, %V
%trunc = fptrunc <1 x double> %frem to <1 x float>
ret <1 x float> %trunc
; CHECK-LABEL: @test6
; CHECK-NEXT: %[[frem:.*]] = frem <1 x double> %V, %V
; CHECK-NEXT: %[[trunc:.*]] = fptrunc <1 x double> %[[frem]] to <1 x float>
; CHECK-NEXT: ret <1 x float> %trunc
}