[InstCombine] Add extra test for eq of parts fold (NFC)

To guard against regression from #112704.

Author: nikic

llvm/test/Transforms/InstCombine/eq-of-parts.ll

@@ -1538,3 +1538,28 @@ define i1 @or_trunc_i1_wrong_operands(i64 %a1, i64 %a2, i64 %a3) {
   %or = or i1 %cmp, %trunc
   ret i1 %or
 }
+
+define i1 @jv_identical(i64 %arg1, i64 %arg2) {
+; CHECK-LABEL: @jv_identical(
+; CHECK-NEXT:    [[ARG1_TRUNC:%.*]] = trunc i64 [[ARG1:%.*]] to i8
+; CHECK-NEXT:    [[ARG2_TRUNC:%.*]] = trunc i64 [[ARG2:%.*]] to i8
+; CHECK-NEXT:    [[EQ1:%.*]] = icmp eq i8 [[ARG1_TRUNC]], [[ARG2_TRUNC]]
+; CHECK-NEXT:    [[DOTUNSHIFTED:%.*]] = xor i64 [[ARG2]], [[ARG1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i64 [[DOTUNSHIFTED]], 65536
+; CHECK-NEXT:    [[AND2:%.*]] = and i1 [[EQ1]], [[TMP1]]
+; CHECK-NEXT:    ret i1 [[AND2]]
+;
+  %arg1.trunc = trunc i64 %arg1 to i8
+  %arg1.shift = lshr i64 %arg1, 16
+  %arg1.shift.trunc = trunc i64 %arg1.shift to i16
+  %arg2.trunc = trunc i64 %arg2 to i8
+  %arg2.shift = lshr i64 %arg2, 16
+  %arg2.shift.trunc = trunc i64 %arg2.shift to i16
+  %eq1 = icmp eq i8 %arg1.trunc, %arg2.trunc
+  %eq2 = icmp eq i16 %arg1.shift.trunc, %arg2.shift.trunc
+  %and1 = and i1 %eq1, %eq2
+  %xor = xor i64 %arg2, %arg1
+  %cmp = icmp ult i64 %xor, 4294967296
+  %and2 = and i1 %cmp, %and1
+  ret i1 %and2
+}