AMDGPU: Fold bitcasts of scalar constants to vectors

This cleans up some messes since the individual scalar components
can be CSEed.

llvm-svn: 266376

1 files changed, 34 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
index 75afce0534b..0d325a32347 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
@@ -399,6 +399,8 @@ AMDGPUTargetLowering::AMDGPUTargetLowering(TargetMachine &TM,
   setTargetDAGCombine(ISD::FADD);
   setTargetDAGCombine(ISD::FSUB);
 
+  setTargetDAGCombine(ISD::BITCAST);
+
   setBooleanContents(ZeroOrNegativeOneBooleanContent);
   setBooleanVectorContents(ZeroOrNegativeOneBooleanContent);
 
@@ -2547,6 +2549,38 @@ SDValue AMDGPUTargetLowering::PerformDAGCombine(SDNode *N,
   switch(N->getOpcode()) {
   default:
     break;
+  case ISD::BITCAST: {
+    EVT DestVT = N->getValueType(0);
+    if (DestVT.getSizeInBits() != 64 && !DestVT.isVector())
+      break;
+
+    // Fold bitcasts of constants.
+    //
+    // v2i32 (bitcast i64:k) -> build_vector lo_32(k), hi_32(k)
+    // TODO: Generalize and move to DAGCombiner
+    SDValue Src = N->getOperand(0);
+    if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Src)) {
+      assert(Src.getValueType() == MVT::i64);
+      SDLoc SL(N);
+      uint64_t CVal = C->getZExtValue();
+      return DAG.getNode(ISD::BUILD_VECTOR, SL, DestVT,
+                         DAG.getConstant(Lo_32(CVal), SL, MVT::i32),
+                         DAG.getConstant(Hi_32(CVal), SL, MVT::i32));
+    }
+
+    if (ConstantFPSDNode *C = dyn_cast<ConstantFPSDNode>(Src)) {
+      const APInt &Val = C->getValueAPF().bitcastToAPInt();
+      SDLoc SL(N);
+      uint64_t CVal = Val.getZExtValue();
+      SDValue Vec = DAG.getNode(ISD::BUILD_VECTOR, SL, MVT::v2i32,
+                                DAG.getConstant(Lo_32(CVal), SL, MVT::i32),
+                                DAG.getConstant(Hi_32(CVal), SL, MVT::i32));
+
+      return DAG.getNode(ISD::BITCAST, SL, DestVT, Vec);
+    }
+
+    break;
+  }
   case ISD::SHL: {
     if (DCI.getDAGCombineLevel() < AfterLegalizeDAG)
       break;