Replace sra with srl if a single sign bit is required
E.g. (and (sra (i32 x) 31) 2) -> (and (srl (i32 x) 30) 2).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192884 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 9d6a3b4..4d30e7b 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -750,13 +750,24 @@
// If the input sign bit is known to be zero, or if none of the top bits
// are demanded, turn this into an unsigned shift right.
- if (KnownZero.intersects(SignBit) || (HighBits & ~NewMask) == HighBits) {
+ if (KnownZero.intersects(SignBit) || (HighBits & ~NewMask) == HighBits)
return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, dl, VT,
Op.getOperand(0),
Op.getOperand(1)));
- } else if (KnownOne.intersects(SignBit)) { // New bits are known one.
- KnownOne |= HighBits;
+
+ int Log2 = NewMask.exactLogBase2();
+ if (Log2 >= 0) {
+ // The bit must come from the sign.
+ SDValue NewSA =
+ TLO.DAG.getConstant(BitWidth - 1 - Log2,
+ Op.getOperand(1).getValueType());
+ return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, dl, VT,
+ Op.getOperand(0), NewSA));
}
+
+ if (KnownOne.intersects(SignBit))
+ // New bits are known one.
+ KnownOne |= HighBits;
}
break;
case ISD::SIGN_EXTEND_INREG: {