RFR: 8372634: C2: Materialize type information from instanceof checks [v2]

[Vladimir Ivanov]

On Thu, 27 Nov 2025 14:56:51 GMT, ExE Boss <duke at openjdk.org> wrote:

>> There are corresponding test cases (`testInstanceOfCondPre` et al) where conditions are embedded.
>> 
>> The idea of `testInstanceOfCondLate` and similar test cases is to check how inlining works when condition improves receiver type during incremental inlining phase.
>
> What I meant was where the `instanceof` is in the called method, the `testInstanceOfCondPre` all have the `instanceof` checks as part of the `if` statement.
> 
> --------------------------------------------------------------------------------
> 
> Something like:
> 
> static void testInstanceOfCondDefaultInlinePre(A a, boolean cond) {
> 	if (defaultInlineInstanceOfCondPre(a, cond)) {
> 		a.m();
> 	}
> }
> static void testInstanceOfCondDefaultInlinePost(A a, boolean cond) {
> 	if (defaultInlineInstanceOfCondPost(a, cond)) {
> 		a.m();
> 	}
> }
> 
> static void testIsInstanceCondDefaultInlinePre(A a, boolean cond) {
> 	if (defaultInlineIsInstanceCondPre(a, cond)) {
> 		a.m();
> 	}
> }
> static void testIsInstanceCondDefaultInlinePost(A a, boolean cond) {
> 	if (defaultInlineIsInstanceCondPost(a, cond)) {
> 		a.m();
> 	}
> }
> 
> 
> --------------------------------------------------------------------------------
> 
> I suggest adding such a test because of real world code which use different internal implementation classes but expose their public API as only a single common supertype, like `java.lang.constant.ClassDesc` and its `isPrimitive()`/`isArray()`/`isClassOrInterface()` methods (which currently don’t do the `instanceof` check, but they probably should so that they can be reliably inlined).

The test is intended as a white-box test. It focuses on bytecode shapes which result in different IR representations and exercise different optimizations. From compiler perspective, there's no difference between  `if (defaultInlineInstanceOfCond(a)) { ... }` and `if (a instanceof B) {...}` when inlining happens during parsing. Both test cases produce the very same IR after parsing is over.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28517#discussion_r2578972141