DAGCombine (shl (anyext x, c)) to (anyext (shl x, c)) if the high bits
are not demanded. This often allows the anyext to be folded away.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109242 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 6e6fede..389f2ea 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1367,9 +1367,29 @@
}
}
- if (SimplifyDemandedBits(Op.getOperand(0), NewMask.lshr(ShAmt),
+ if (SimplifyDemandedBits(InOp, NewMask.lshr(ShAmt),
KnownZero, KnownOne, TLO, Depth+1))
return true;
+
+ // Convert (shl (anyext x, c)) to (anyext (shl x, c)) if the high bits
+ // are not demanded. This will likely allow the anyext to be folded away.
+ if (InOp.getNode()->getOpcode() == ISD::ANY_EXTEND) {
+ SDValue InnerOp = InOp.getNode()->getOperand(0);
+ EVT InnerVT = InnerOp.getValueType();
+ if ((APInt::getHighBitsSet(BitWidth,
+ BitWidth - InnerVT.getSizeInBits()) &
+ DemandedMask) == 0 &&
+ isTypeDesirableForOp(ISD::SHL, InnerVT)) {
+ SDValue NarrowShl =
+ TLO.DAG.getNode(ISD::SHL, dl, InnerVT, InnerOp,
+ TLO.DAG.getConstant(ShAmt, InnerVT));
+ return
+ TLO.CombineTo(Op,
+ TLO.DAG.getNode(ISD::ANY_EXTEND, dl, Op.getValueType(),
+ NarrowShl));
+ }
+ }
+
KnownZero <<= SA->getZExtValue();
KnownOne <<= SA->getZExtValue();
// low bits known zero.