Reimplement r114460 in target-independent DAGCombine rather than target-dependent, by using
the predicate to discover the number of sign bits. Enhance X86's target lowering to provide
a useful response to this query.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114473 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c71b3c0..1bd1e00 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1424,6 +1424,20 @@
N0.getOperand(0).getOperand(1),
N0.getOperand(1)));
+ if (N1.getOpcode() == ISD::AND) {
+ SDValue AndOp0 = N1.getOperand(0);
+ ConstantSDNode *AndOp1 = dyn_cast<ConstantSDNode>(N1->getOperand(1));
+ unsigned NumSignBits = DAG.ComputeNumSignBits(AndOp0);
+ unsigned DestBits = VT.getScalarType().getSizeInBits();
+
+ // (add z, (and (sbbl x, x), 1)) -> (sub z, (sbbl x, x))
+ // and similar xforms where the inner op is either ~0 or 0.
+ if (NumSignBits == DestBits && AndOp1 && AndOp1->isOne()) {
+ DebugLoc DL = N->getDebugLoc();
+ return DAG.getNode(ISD::SUB, DL, VT, N->getOperand(0), AndOp0);
+ }
+ }
+
return SDValue();
}