AMDGPU: Constant fold rcp node

When doing arcp optimization with a constant denominator,
this was leaving behind rcps with constant inputs.

llvm-svn: 297248

1 files changed, 12 insertions, 2 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
index edaab0063da..41a4f762018 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -1295,8 +1295,8 @@ SDValue AMDGPUTargetLowering::LowerDIVREM24(SDValue Op, SelectionDAG &DAG,
   SDValue fqneg = DAG.getNode(ISD::FNEG, DL, FltVT, fq);
 
   // float fr = mad(fqneg, fb, fa);
-  unsigned OpCode = Subtarget->hasFP32Denormals() ? 
-                    (unsigned)AMDGPUISD::FMAD_FTZ : 
+  unsigned OpCode = Subtarget->hasFP32Denormals() ?
+                    (unsigned)AMDGPUISD::FMAD_FTZ :
                     (unsigned)ISD::FMAD;
   SDValue fr = DAG.getNode(OpCode, DL, FltVT, fqneg, fb, fa);
 
@@ -3351,6 +3351,16 @@ SDValue AMDGPUTargetLowering::PerformDAGCombine(SDNode *N,
     return performStoreCombine(N, DCI);
   case AMDGPUISD::CLAMP:
     return performClampCombine(N, DCI);
+  case AMDGPUISD::RCP: {
+    if (const auto *CFP = dyn_cast<ConstantFPSDNode>(N->getOperand(0))) {
+      // XXX - Should this flush denormals?
+      const APFloat &Val = CFP->getValueAPF();
+      APFloat One(Val.getSemantics(), "1.0");
+      return DAG.getConstantFP(One / Val, SDLoc(N), N->getValueType(0));
+    }
+
+    break;
+  }
   }
   return SDValue();
 }