[InstCombine] Keep or disjoint after folding casted bitwise logic

Optimize
`or disjoint (zext/sext a) (zext/sext b))`
to
`(zext/sext (or disjoint a, b))`
without losing disjoint.

Confirmed by: https://alive2.llvm.org/ce/z/kQ5fJv.

Author: tclin914

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -1869,6 +1869,9 @@ Instruction *InstCombinerImpl::foldCastedBitwiseLogic(BinaryOperator &I) {
 
     // Do the logic op in the intermediate width, then widen more.
     Value *NarrowLogic = Builder.CreateBinOp(LogicOpc, X, Y, I.getName());
+    if (auto *Disjoint = dyn_cast<PossiblyDisjointInst>(&I);
+        Disjoint && Disjoint->isDisjoint())
+      cast<PossiblyDisjointInst>(NarrowLogic)->setIsDisjoint(true);
     return CastInst::Create(CastOpcode, NarrowLogic, DestTy);
   }
 

llvm/test/Transforms/InstCombine/and-xor-or.ll

@@ -4338,7 +4338,7 @@ define i16 @or_disjoint_zext_zext(i8 %x, i4 %y) {
 ; CHECK-LABEL: define {{[^@]+}}@or_disjoint_zext_zext
 ; CHECK-SAME: (i8 [[X:%.*]], i4 [[Y:%.*]]) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext i4 [[Y]] to i8
-; CHECK-NEXT:    [[R1:%.*]] = or i8 [[X]], [[TMP1]]
+; CHECK-NEXT:    [[R1:%.*]] = or disjoint i8 [[X]], [[TMP1]]
 ; CHECK-NEXT:    [[R:%.*]] = zext i8 [[R1]] to i16
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
@@ -4481,7 +4481,7 @@ define i16 @or_disjoint_sext_sext(i8 %x, i4 %y) {
 ; CHECK-LABEL: define {{[^@]+}}@or_disjoint_sext_sext
 ; CHECK-SAME: (i8 [[X:%.*]], i4 [[Y:%.*]]) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = sext i4 [[Y]] to i8
-; CHECK-NEXT:    [[R1:%.*]] = or i8 [[X]], [[TMP1]]
+; CHECK-NEXT:    [[R1:%.*]] = or disjoint i8 [[X]], [[TMP1]]
 ; CHECK-NEXT:    [[R:%.*]] = sext i8 [[R1]] to i16
 ; CHECK-NEXT:    ret i16 [[R]]
 ;