The DAG combiner was performing a BT combine. The BT combine had a value of -1,
so it changed it into a 31 via the TLO.ShrinkDemandedConstant() call. Then it
would go through the DAG combiner again. This time it had a value of 31, which
was turned into a -1 by TLI.SimplifyDemandedBits(). This would ping pong
forever.
Teach the TLO.ShrinkDemandedConstant() call not to lower a value if the demanded
value is an XOR of all ones.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65985 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index e92932b..7913c01 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -746,23 +746,34 @@
bool TargetLowering::TargetLoweringOpt::ShrinkDemandedConstant(SDValue Op,
const APInt &Demanded) {
DebugLoc dl = Op.getDebugLoc();
+
// FIXME: ISD::SELECT, ISD::SELECT_CC
switch (Op.getOpcode()) {
default: break;
- case ISD::AND:
- case ISD::OR:
case ISD::XOR:
- if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
- if (C->getAPIntValue().intersects(~Demanded)) {
- MVT VT = Op.getValueType();
- SDValue New = DAG.getNode(Op.getOpcode(), dl, VT, Op.getOperand(0),
- DAG.getConstant(Demanded &
- C->getAPIntValue(),
- VT));
- return CombineTo(Op, New);
- }
+ case ISD::AND:
+ case ISD::OR: {
+ ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1));
+ if (!C) return false;
+
+ if (Op.getOpcode() == ISD::XOR &&
+ (C->getAPIntValue() | (~Demanded)).isAllOnesValue())
+ return false;
+
+ // if we can expand it to have all bits set, do it
+ if (C->getAPIntValue().intersects(~Demanded)) {
+ MVT VT = Op.getValueType();
+ SDValue New = DAG.getNode(Op.getOpcode(), dl, VT, Op.getOperand(0),
+ DAG.getConstant(Demanded &
+ C->getAPIntValue(),
+ VT));
+ return CombineTo(Op, New);
+ }
+
break;
}
+ }
+
return false;
}