[InstCombine] Preserve disjoint or after folding casted bitwise logic (#136815)

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

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

Author: tclin914

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -1869,6 +1869,10 @@ 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());
+    auto *Disjoint = dyn_cast<PossiblyDisjointInst>(&I);
+    auto *NewDisjoint = dyn_cast<PossiblyDisjointInst>(NarrowLogic);
+    if (Disjoint && NewDisjoint)
+      NewDisjoint->setIsDisjoint(Disjoint->isDisjoint());
     return CastInst::Create(CastOpcode, NarrowLogic, DestTy);
   }
 

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

@@ -4334,6 +4334,33 @@ define i16 @or_zext_zext_2_use1(i8 %x, i8 %y) {
   ret i16 %r
 }
 
+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 disjoint i8 [[X]], [[TMP1]]
+; CHECK-NEXT:    [[R:%.*]] = zext i8 [[R1]] to i16
+; CHECK-NEXT:    ret i16 [[R]]
+;
+  %zx = zext i8 %x to i16
+  %zy = zext i4 %y to i16
+  %r = or disjoint i16 %zy, %zx
+  ret i16 %r
+}
+
+define i16 @or_disjoint_zext_zext_2(i8 %x, i8 %y) {
+; CHECK-LABEL: define {{[^@]+}}@or_disjoint_zext_zext_2
+; CHECK-SAME: (i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[R1:%.*]] = or disjoint i8 [[Y]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = zext i8 [[R1]] to i16
+; CHECK-NEXT:    ret i16 [[R]]
+;
+  %zx = zext i8 %x to i16
+  %zy = zext i8 %y to i16
+  %r = or disjoint i16 %zy, %zx
+  ret i16 %r
+}
+
 define <2 x i16> @xor_zext_zext(<2 x i8> %x, <2 x i4> %y) {
 ; CHECK-LABEL: define {{[^@]+}}@xor_zext_zext
 ; CHECK-SAME: (<2 x i8> [[X:%.*]], <2 x i4> [[Y:%.*]]) {
@@ -4463,6 +4490,33 @@ define i16 @or_sext_sext_2_use1(i8 %x, i8 %y) {
   ret i16 %r
 }
 
+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 disjoint i8 [[X]], [[TMP1]]
+; CHECK-NEXT:    [[R:%.*]] = sext i8 [[R1]] to i16
+; CHECK-NEXT:    ret i16 [[R]]
+;
+  %sx = sext i8 %x to i16
+  %sy = sext i4 %y to i16
+  %r = or disjoint i16 %sx, %sy
+  ret i16 %r
+}
+
+define i16 @or_disjoint_sext_sext_2(i8 %x, i8 %y) {
+; CHECK-LABEL: define {{[^@]+}}@or_disjoint_sext_sext_2
+; CHECK-SAME: (i8 [[X:%.*]], i8 [[Y:%.*]]) {
+; CHECK-NEXT:    [[R1:%.*]] = or disjoint i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[R:%.*]] = sext i8 [[R1]] to i16
+; CHECK-NEXT:    ret i16 [[R]]
+;
+  %sx = sext i8 %x to i16
+  %sy = sext i8 %y to i16
+  %r = or disjoint i16 %sx, %sy
+  ret i16 %r
+}
+
 define i16 @xor_sext_sext(i8 %x, i4 %y) {
 ; CHECK-LABEL: define {{[^@]+}}@xor_sext_sext
 ; CHECK-SAME: (i8 [[X:%.*]], i4 [[Y:%.*]]) {