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InstCombine: Fix another infinite loop caused by visitFPTrunc

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We would attempt to replace an frem's operand with the same operand.
This would cause InstCombine to think real work was done, causing
InstCombine to enter an infinite loop.

This fixes the second part of PR21576.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222265 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-11-18 22:06:45 +00:00
parent ed37b1e2d0
commit 643bef9333
2 changed files with 14 additions and 5 deletions
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9
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -1269,13 +1269,12 @@ 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)
NewLHS = Builder->CreateFPExt(NewLHS, RHSOrig->getType());
LHSOrig = Builder->CreateFPExt(LHSOrig, RHSOrig->getType());
else if (RHSWidth <= SrcWidth)
NewRHS = Builder->CreateFPExt(NewRHS, LHSOrig->getType());
if (NewLHS != LHSOrig || NewRHS != RHSOrig) {
Value *ExactResult = Builder->CreateFRem(NewLHS, NewRHS);
RHSOrig = Builder->CreateFPExt(RHSOrig, LHSOrig->getType());
if (LHSOrig != OpI->getOperand(0) || RHSOrig != OpI->getOperand(1)) {
Value *ExactResult = Builder->CreateFRem(LHSOrig, RHSOrig);
if (Instruction *RI = dyn_cast<Instruction>(ExactResult))
RI->copyFastMathFlags(OpI);
return CastInst::CreateFPCast(ExactResult, CI.getType());

10
test/Transforms/InstCombine/fpcast.ll
View File

@ -63,3 +63,13 @@ define <1 x float> @test6(<1 x double> %V) {
; CHECK-NEXT: %[[trunc:.*]] = fptrunc <1 x double> %[[frem]] to <1 x float>
; CHECK-NEXT: ret <1 x float> %trunc
}
define float @test7(double %V) {
%frem = frem double %V, 1.000000e+00
%trunc = fptrunc double %frem to float
ret float %trunc
; CHECK-LABEL: @test7
; CHECK-NEXT: %[[frem:.*]] = frem double %V, 1.000000e+00
; CHECK-NEXT: %[[trunc:.*]] = fptrunc double %frem to float
; CHECK-NEXT: ret float %trunc
}