InstCombine: fold fcmp pred (fneg x), C -> fcmp swap(pred) x, -C

llvm-svn: 128626

2 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 48ce7cffb58..6743885cd42 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2834,6 +2834,14 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
           return SelectInst::Create(LHSI->getOperand(0), Op1, Op2);
         break;
       }
+      case Instruction::FSub: {
+        // fcmp pred (fneg x), C -> fcmp swap(pred) x, -C
+        Value *Op;
+        if (match(LHSI, m_FNeg(m_Value(Op))))
+          return new FCmpInst(I.getSwappedPredicate(), Op,
+                              ConstantExpr::getFNeg(RHSC));
+        break;
+      }
       case Instruction::Load:
         if (GetElementPtrInst *GEP =
             dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) {
diff --git a/llvm/test/Transforms/InstCombine/fcmp.ll b/llvm/test/Transforms/InstCombine/fcmp.ll
index 49bd50717dc..f869a18992d 100644
--- a/llvm/test/Transforms/InstCombine/fcmp.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp.ll
@@ -32,3 +32,11 @@ define i1 @test4(float %a) nounwind {
 ; CHECK: @test4
 ; CHECK-NEXT: fpext float %a to double
 }
+
+define i1 @test5(float %a) nounwind {
+  %neg = fsub float -0.000000e+00, %a
+  %cmp = fcmp ogt float %neg, 1.000000e+00
+  ret i1 %cmp
+; CHECK: @test5
+; CHECK-NEXT: fcmp olt float %a, -1.0
+}