RFR: 8356865: C2: Unreasonable values for debug flag FastAllocateSizeLimit can lead to left-shift-overflow, which is UB [v2]

[Benoît Maillard]

On Tue, 17 Jun 2025 08:36:39 GMT, Manuel Hässig <mhaessig at openjdk.org> wrote:

>> Benoît Maillard has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8356865: Add comment to clarify the flag range
>
> src/hotspot/share/runtime/globals.hpp line 1100:
> 
>> 1098:           /* Note:  This value is zero mod 1<<13 for a cheap sparc set. */  \
>> 1099:           "Inline allocations larger than this in doublewords must go slow")\
>> 1100:           range(0, (1 << (BitsPerInt - LogBytesPerLong - 1)) - 1)           \
> 
> It would be good to add a comment as to why this specific upper limit is necessary.

Thanks, done!

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PR Review Comment: https://git.openjdk.org/jdk/pull/25834#discussion_r2153848744