Fix another infinite loop in InstCombine

Summary:
InstCombine infinite-loops for the testcase added
It is because InstCombine is generating instructions that can be
optimized by itself. Fix by not optimizing frem if the optimized
type is the same as original type.
rdar://problem/19150820

Reviewers: majnemer

Differential Revision: http://reviews.llvm.org/D6634

llvm-svn: 224097

2 files changed, 24 insertions, 9 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index aba77bb4462..357bf24ebe2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1269,16 +1269,19 @@ 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.
-        if (LHSWidth < SrcWidth)
-          LHSOrig = Builder->CreateFPExt(LHSOrig, RHSOrig->getType());
-        else if (RHSWidth <= SrcWidth)
-          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());
+        if (SrcWidth != OpWidth) {
+          if (LHSWidth < SrcWidth)
+            LHSOrig = Builder->CreateFPExt(LHSOrig, RHSOrig->getType());
+          else if (RHSWidth <= SrcWidth)
+            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());
+          }
         }
+        break;
     }
 
     // (fptrunc (fneg x)) -> (fneg (fptrunc x))
diff --git a/llvm/test/Transforms/InstCombine/fpcast.ll b/llvm/test/Transforms/InstCombine/fpcast.ll
index ac034028b22..8319624b87c 100644
--- a/llvm/test/Transforms/InstCombine/fpcast.ll
+++ b/llvm/test/Transforms/InstCombine/fpcast.ll
@@ -73,3 +73,15 @@ define float @test7(double %V) {
 ; CHECK-NEXT: %[[trunc:.*]] = fptrunc double %frem to float
 ; CHECK-NEXT: ret float %trunc
 }
+
+define float @test8(float %V) {
+  %fext = fpext float %V to double
+  %frem = frem double %fext, 1.000000e-01
+  %trunc = fptrunc double %frem to float
+  ret float %trunc
+; CHECK-LABEL: @test8
+; CHECK-NEXT: %[[fext:.*]]  = fpext float %V to double
+; CHECK-NEXT: %[[frem:.*]]  = frem double %fext, 1.000000e-01
+; CHECK-NEXT: %[[trunc:.*]] = fptrunc double %frem to float
+; CHECK-NEXT: ret float %trunc
+}