[llvm] r224097 - Fix another infinite loop in InstCombine

[Steven Wu]

Author: steven_wu
Date: Thu Dec 11 22:34:07 2014
New Revision: 224097

URL: http://llvm.org/viewvc/llvm-project?rev=224097&view=rev
Log:
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

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/trunk/test/Transforms/InstCombine/fpcast.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=224097&r1=224096&r2=224097&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Thu Dec 11 22:34:07 2014
@@ -1269,16 +1269,19 @@ Instruction *InstCombiner::visitFPTrunc(
         // 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))

Modified: llvm/trunk/test/Transforms/InstCombine/fpcast.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fpcast.ll?rev=224097&r1=224096&r2=224097&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/fpcast.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/fpcast.ll Thu Dec 11 22:34:07 2014
@@ -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
+}