RFR: 8358781: C2 fails with assert "bad profile data type" when TypeProfileCasts is disabled [v2]

[Manuel Hässig]

On Tue, 12 Aug 2025 08:56:02 GMT, Saranya Natarajan <snatarajan at openjdk.org> wrote:

>> **Issue**
>> An error, `assert(data->is_ReceiverTypeData()) failed: bad profile data type`, is encountered during C2 compilation due to bad profile data. This occurs when the code is compiled with `TypeProfileCasts` option disabled. 
>> 
>> **Analysis** 
>> The assertion failure occurs in `record_profiled_receiver_for_speculation` that analyzes the profiling information in the method data to determine whether a null value has been observed in the `instanceof` operation. This information is encoded in the `BitData` during profiling. When the method identifies that a null has been seen, it proceeds to inspect the associated `ReceiverTypeData` to see if the  type check is always performed against null. However, in this scenario, the incoming profiling data is of type `BitData` rather than `ReceiverTypeData`, leading to the assertion failure. 
>> 
>> The profiling information for null seen for operations `aastore`, `instanceof`, and `checkcast` is recorded by the method `profile_null_seen `(in` src/hotspot/cpu/x86/templateTable_x86.cpp `). On investigating this method, it can be observed that the method data pointer is not updated for `VirtualCallData` (which is a subclass of `ReceiverTypeData`) when the `TypeProfileCasts` option is disabled. 
>> 
>> **Solution** 
>> My proposal is to inspect the `ReceiverTypeData` in function `record_profiled_receiver_for_speculation` only if `TypeProfileCasts` is enabled (this is based on the fact that the relevant method data pointer is not updated when `TypeProfileCasts` is disabled).
>> 
>> **Question to reviewers** 
>> Do you think this is a reasonable fix ?
>> 
>> **Testing**
>> GitHub Actions
>> tier1 to tier3 on windows-x64, linux-x64, linux-aarch64, macosx-x64, and macosx-aarch64.
>
> Saranya Natarajan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   adding test

Thank you for adding the test. Apart from my question, this looks good to me.

test/hotspot/jtreg/compiler/arguments/TestProfileCasts.java line 43:

> 41: 
> 42:     public static void main(String[] args) {
> 43:         for (int i = 0; i < 100_000; i++) {

Do you really need 100'000 iterations to get it to compile or can you reduce it a bit?

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Marked as reviewed by mhaessig (Committer).

PR Review: https://git.openjdk.org/jdk/pull/26640#pullrequestreview-3109559187
PR Review Comment: https://git.openjdk.org/jdk/pull/26640#discussion_r2269272446