[InstCombine] Use disjoint flag for alternate binops

Check the or disjoint flag instead of the weaker MaskedValueIsZero
query.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

@@ -2072,9 +2072,8 @@ static BinopElts getAlternateBinop(BinaryOperator *BO, const DataLayout &DL) {
     break;
   }
   case Instruction::Or: {
-    // or X, C --> add X, C (when X and C have no common bits set)
-    const APInt *C;
-    if (match(BO1, m_APInt(C)) && MaskedValueIsZero(BO0, *C, DL))
+    // or disjoin X, C --> add X, C
+    if (cast<PossiblyDisjointInst>(BO)->isDisjoint())
       return {Instruction::Add, BO0, BO1};
     break;
   }

llvm/test/Transforms/InstCombine/shuffle_select.ll

@@ -1466,6 +1466,17 @@ define <4 x i32> @add_or(<4 x i32> %v) {
   ret <4 x i32> %t3
 }
 
+define <4 x i32> @add_or_disjoint(<4 x i32> %v) {
+; CHECK-LABEL: @add_or_disjoint(
+; CHECK-NEXT:    [[T3:%.*]] = add <4 x i32> [[V:%.*]], <i32 31, i32 31, i32 65536, i32 65537>
+; CHECK-NEXT:    ret <4 x i32> [[T3]]
+;
+  %t1 = add <4 x i32> %v, <i32 65534, i32 65535, i32 65536, i32 65537>
+  %t2 = or disjoint <4 x i32> %v, <i32 31, i32 31, i32 31, i32 31>
+  %t3 = shufflevector <4 x i32> %t1, <4 x i32> %t2, <4 x i32> <i32 4, i32 5, i32 2, i32 3>
+  ret <4 x i32> %t3
+}
+
 ; Try with 'or' as operand 0 of the shuffle.
 
 define <4 x i8> @or_add(<4 x i8> %v) {