[TargetLowering] SimplifyDemandedBits - add ANY_EXTEND_VECTOR_INREG support

Add 'lowest' demanded elt -> bitcast fold to all *_EXTEND_VECTOR_INREG cases.

Reapplies rL363856.

llvm-svn: 364311

1 files changed, 18 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 933d4f3c..d83bd10 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1415,6 +1415,13 @@ bool TargetLowering::SimplifyDemandedBits(
 
     // If none of the top bits are demanded, convert this into an any_extend.
     if (DemandedBits.getActiveBits() <= InBits) {
+      // If we only need the non-extended bits of the bottom element
+      // then we can just bitcast to the result.
+      if (IsVecInReg && DemandedElts == 1 &&
+          VT.getSizeInBits() == SrcVT.getSizeInBits() &&
+          TLO.DAG.getDataLayout().isLittleEndian())
+        return TLO.CombineTo(Op, TLO.DAG.getBitcast(VT, Src));
+
       unsigned Opc =
           IsVecInReg ? ISD::ANY_EXTEND_VECTOR_INREG : ISD::ANY_EXTEND;
       if (!TLO.LegalOperations() || isOperationLegal(Opc, VT))
@@ -1446,12 +1453,21 @@ bool TargetLowering::SimplifyDemandedBits(
     }
     break;
   }
-  case ISD::ANY_EXTEND: {
-    // TODO: Add ISD::ANY_EXTEND_VECTOR_INREG support.
+  case ISD::ANY_EXTEND:
+  case ISD::ANY_EXTEND_VECTOR_INREG: {
     SDValue Src = Op.getOperand(0);
     EVT SrcVT = Src.getValueType();
     unsigned InBits = SrcVT.getScalarSizeInBits();
     unsigned InElts = SrcVT.isVector() ? SrcVT.getVectorNumElements() : 1;
+    bool IsVecInReg = Op.getOpcode() == ISD::ANY_EXTEND_VECTOR_INREG;
+
+    // If we only need the bottom element then we can just bitcast.
+    // TODO: Handle ANY_EXTEND?
+    if (IsVecInReg && DemandedElts == 1 &&
+        VT.getSizeInBits() == SrcVT.getSizeInBits() &&
+        TLO.DAG.getDataLayout().isLittleEndian())
+      return TLO.CombineTo(Op, TLO.DAG.getBitcast(VT, Src));
+
     APInt InDemandedBits = DemandedBits.trunc(InBits);
     APInt InDemandedElts = DemandedElts.zextOrSelf(InElts);
     if (SimplifyDemandedBits(Src, InDemandedBits, InDemandedElts, Known, TLO,