InstCombine: Fix another infinite loop caused by visitFPTrunc

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.

llvm-svn: 222265

1 files changed, 4 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index a0570f7ebd4..aba77bb4462 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -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());