Handle a special case xor undef, undef -> 0. Technically this should be transformed to undef. But this is such a common idiom (misuse) we are going to handle it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48792 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 2229743..e24a294 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2119,6 +2119,9 @@
if (FoldedVOp.Val) return FoldedVOp;
}
+ // fold (xor undef, undef) -> 0. This is a common idiom (misuse).
+ if (N0.getOpcode() == ISD::UNDEF && N1.getOpcode() == ISD::UNDEF)
+ return DAG.getConstant(0, VT);
// fold (xor x, undef) -> undef
if (N0.getOpcode() == ISD::UNDEF)
return N0;
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 05f7edb..ed564b2 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2245,6 +2245,12 @@
// Fold a bunch of operators when the RHS is undef.
if (N2.getOpcode() == ISD::UNDEF) {
switch (Opcode) {
+ case ISD::XOR:
+ if (N1.getOpcode() == ISD::UNDEF)
+ // Handle undef ^ undef -> 0 special case. This is a common
+ // idiom (misuse).
+ return getConstant(0, VT);
+ // fallthrough
case ISD::ADD:
case ISD::ADDC:
case ISD::ADDE:
@@ -2258,7 +2264,6 @@
case ISD::SDIV:
case ISD::UREM:
case ISD::SREM:
- case ISD::XOR:
return N2; // fold op(arg1, undef) -> undef
case ISD::MUL:
case ISD::AND: