[InstCombine] Explicitly set disjoint flag when converting xor to or. (#74229)

Author: topperc

llvm/include/llvm/IR/InstrTypes.h

@@ -336,6 +336,15 @@ class BinaryOperator : public Instruction {
     return BO;
   }
 
+  static inline BinaryOperator *
+  CreateDisjoint(BinaryOps Opc, Value *V1, Value *V2, const Twine &Name = "");
+  static inline BinaryOperator *CreateDisjoint(BinaryOps Opc, Value *V1,
+                                               Value *V2, const Twine &Name,
+                                               BasicBlock *BB);
+  static inline BinaryOperator *CreateDisjoint(BinaryOps Opc, Value *V1,
+                                               Value *V2, const Twine &Name,
+                                               Instruction *I);
+
 #define DEFINE_HELPERS(OPC, NUWNSWEXACT)                                       \
   static BinaryOperator *Create##NUWNSWEXACT##OPC(Value *V1, Value *V2,        \
                                                   const Twine &Name = "") {    \
@@ -364,6 +373,8 @@ class BinaryOperator : public Instruction {
   DEFINE_HELPERS(AShr, Exact)  // CreateExactAShr
   DEFINE_HELPERS(LShr, Exact)  // CreateExactLShr
 
+  DEFINE_HELPERS(Or, Disjoint) // CreateDisjointOr
+
 #undef DEFINE_HELPERS
 
   /// Helper functions to construct and inspect unary operations (NEG and NOT)
@@ -438,6 +449,27 @@ class PossiblyDisjointInst : public BinaryOperator {
   }
 };
 
+BinaryOperator *BinaryOperator::CreateDisjoint(BinaryOps Opc, Value *V1,
+                                               Value *V2, const Twine &Name) {
+  BinaryOperator *BO = Create(Opc, V1, V2, Name);
+  cast<PossiblyDisjointInst>(BO)->setIsDisjoint(true);
+  return BO;
+}
+BinaryOperator *BinaryOperator::CreateDisjoint(BinaryOps Opc, Value *V1,
+                                               Value *V2, const Twine &Name,
+                                               BasicBlock *BB) {
+  BinaryOperator *BO = Create(Opc, V1, V2, Name, BB);
+  cast<PossiblyDisjointInst>(BO)->setIsDisjoint(true);
+  return BO;
+}
+BinaryOperator *BinaryOperator::CreateDisjoint(BinaryOps Opc, Value *V1,
+                                               Value *V2, const Twine &Name,
+                                               Instruction *I) {
+  BinaryOperator *BO = Create(Opc, V1, V2, Name, I);
+  cast<PossiblyDisjointInst>(BO)->setIsDisjoint(true);
+  return BO;
+}
+
 //===----------------------------------------------------------------------===//
 //                               CastInst Class
 //===----------------------------------------------------------------------===//

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

@@ -1582,11 +1582,8 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
 
   // A+B --> A|B iff A and B have no bits set in common.
   WithCache<const Value *> LHSCache(LHS), RHSCache(RHS);
-  if (haveNoCommonBitsSet(LHSCache, RHSCache, SQ.getWithInstruction(&I))) {
-    auto *Or = BinaryOperator::CreateOr(LHS, RHS);
-    cast<PossiblyDisjointInst>(Or)->setIsDisjoint(true);
-    return Or;
-  }
+  if (haveNoCommonBitsSet(LHSCache, RHSCache, SQ.getWithInstruction(&I)))
+    return BinaryOperator::CreateDisjointOr(LHS, RHS);
 
   if (Instruction *Ext = narrowMathIfNoOverflow(I))
     return Ext;

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -4462,7 +4462,7 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
   Value *M;
   if (match(&I, m_c_Xor(m_c_And(m_Not(m_Value(M)), m_Value()),
                         m_c_And(m_Deferred(M), m_Value()))))
-    return BinaryOperator::CreateOr(Op0, Op1);
+    return BinaryOperator::CreateDisjointOr(Op0, Op1);
 
   if (Instruction *Xor = visitMaskedMerge(I, Builder))
     return Xor;

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -315,6 +315,8 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     if (DemandedMask.isSubsetOf(RHSKnown.Zero | LHSKnown.Zero)) {
       Instruction *Or =
           BinaryOperator::CreateOr(I->getOperand(0), I->getOperand(1));
+      if (DemandedMask.isAllOnes())
+        cast<PossiblyDisjointInst>(Or)->setIsDisjoint(true);
       Or->takeName(I);
       return InsertNewInstWith(Or, I->getIterator());
     }