[TargetLowering] SimplifyDemandedBits - add EXTRACT_SUBVECTOR support.

Call SimplifyDemandedBits on the source vector.

llvm-svn: 371923

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 4fc9f2465d3..41b3ba1733d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -907,6 +907,21 @@ bool TargetLowering::SimplifyDemandedBits(
     }
     break;
   }
+  case ISD::EXTRACT_SUBVECTOR: {
+    // If index isn't constant, assume we need all the source vector elements.
+    SDValue Src = Op.getOperand(0);
+    ConstantSDNode *SubIdx = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+    unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
+    APInt SrcElts = APInt::getAllOnesValue(NumSrcElts);
+    if (SubIdx && SubIdx->getAPIntValue().ule(NumSrcElts - NumElts)) {
+      // Offset the demanded elts by the subvector index.
+      uint64_t Idx = SubIdx->getZExtValue();
+      SrcElts = DemandedElts.zextOrSelf(NumSrcElts).shl(Idx);
+    }
+    if (SimplifyDemandedBits(Src, DemandedBits, SrcElts, Known, TLO, Depth + 1))
+      return true;
+    break;
+  }
   case ISD::CONCAT_VECTORS: {
     Known.Zero.setAllBits();
     Known.One.setAllBits();