RFR: 8278871: [JVMCI] assert((uint)reason < 2* _trap_hist_limit) failed: oob

[Tom Rodriguez]

On Wed, 15 Dec 2021 23:11:58 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

> This PR fixes a discrepancy between `MethodData::_trap_hist_list` and `Deoptimization::Reason_LIMIT` in terms of JVMCI specific usage.
> 
> JVMCI doubles the size of the deopt history for a method so that it can distinguish deopts in a normal method compilation from deopts in an OSR compilation:
> 
>     union {
>       intptr_t _align;
>       u1 _array[JVMCI_ONLY(2 *) MethodData::_trap_hist_limit];
>     } _trap_hist;
> 
> 
> To access the history for OSR deopts, the index for a deopt reason needs to be adjusted to the upper half of the history array. The amount used for the adjustment was incorrect and this PR fixes it:
> 
> 
>   if (update_total_trap_count) {
>     uint idx = reason;
> #if INCLUDE_JVMCI
>     if (is_osr) {
>       idx += Reason_TRAP_HISTORY_LENGTH;
>     }
> #endif
> 
> 
> I introduced `Reason_TRAP_HISTORY_LENGTH` as a replacement for `25 JVMCI_ONLY(+5),  // decoupled from Deoptimization::Reason_LIMIT` as this decoupling is unnecessary (as dangerous) as far as I can see.

Marked as reviewed by never (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/6855