[SelectionDAG][X86] Add a NoWrap flag to SelectionDAG::isAddLike. NFC (#90681)

If this flag is set, Xor will not be considered AddLike. If an Xor were
treated as an Add it may wrap. If we can prove there would be no carry out and
thus no wrap, the Xor would be turned into a disjoint Or by DAGCombine.

Use this new flag to fix a bug in X86 where an Xor is incorrectly being treated
as an NUWAdd.

Fixes #90668.

Author: topperc

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -2083,8 +2083,9 @@ class SelectionDAG {
   /// Return true if the specified operand is an ISD::OR or ISD::XOR node
   /// that can be treated as an ISD::ADD node.
   /// or(x,y) == add(x,y) iff haveNoCommonBitsSet(x,y)
-  /// xor(x,y) == add(x,y) iff isMinSignedConstant(y)
-  bool isADDLike(SDValue Op) const;
+  /// xor(x,y) == add(x,y) iff isMinSignedConstant(y) && !NoWrap
+  /// If \p NoWrap is true, this will not match ISD::XOR.
+  bool isADDLike(SDValue Op, bool NoWrap = false) const;
 
   /// Return true if the specified operand is an ISD::ADD with a ConstantSDNode
   /// on the right-hand side, or if it is an ISD::OR with a ConstantSDNode that

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -5231,13 +5231,13 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   return true;
 }
 
-bool SelectionDAG::isADDLike(SDValue Op) const {
+bool SelectionDAG::isADDLike(SDValue Op, bool NoWrap) const {
   unsigned Opcode = Op.getOpcode();
   if (Opcode == ISD::OR)
     return Op->getFlags().hasDisjoint() ||
            haveNoCommonBitsSet(Op.getOperand(0), Op.getOperand(1));
   if (Opcode == ISD::XOR)
-    return isMinSignedConstant(Op.getOperand(1));
+    return !NoWrap && isMinSignedConstant(Op.getOperand(1));
   return false;
 }
 

llvm/lib/Target/X86/X86ISelDAGToDAG.cpp

@@ -2353,7 +2353,7 @@ SDValue X86DAGToDAGISel::matchIndexRecursively(SDValue N,
     SDValue Src = N.getOperand(0);
     unsigned SrcOpc = Src.getOpcode();
     if (((SrcOpc == ISD::ADD && Src->getFlags().hasNoUnsignedWrap()) ||
-         CurDAG->isADDLike(Src)) &&
+         CurDAG->isADDLike(Src, /*NoWrap=*/true)) &&
         Src.hasOneUse()) {
       if (CurDAG->isBaseWithConstantOffset(Src)) {
         SDValue AddSrc = Src.getOperand(0);

llvm/test/CodeGen/X86/pr90668.ll

@@ -4,8 +4,9 @@
 define i64 @off(i8 signext %a) {
 ; CHECK-LABEL: off:
 ; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    addb $-128, %dil
 ; CHECK-NEXT:    movzbl %dil, %eax
-; CHECK-NEXT:    leal 1024(,%rax,8), %eax
+; CHECK-NEXT:    shll $3, %eax
 ; CHECK-NEXT:    retq
 entry:
   %add = xor i8 %a, -128