RFR: 8359920: Use names for frame types in stackmaps [v2]

[Coleen Phillimore]

On Thu, 19 Jun 2025 06:24:03 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update src/hotspot/share/prims/jvmtiRedefineClasses.cpp
>>   
>>   Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>
>
> src/hotspot/share/classfile/stackMapTable.hpp line 154:
> 
>> 152:     SAME_FRAME = 64,
>> 153:     SAME_LOCALS_1_STACK_ITEM_FRAME = 128,
>> 154:     SAME_LOCALS_1_STACK_ITEM_EXTENDED = 247,
> 
> I find these definitions a little confusing. SAME_FRAME is actually 0-63, with SAME_LOCALS_1_STACK_ITEM_FRAME being 64-127. Given many of these frame types imply tag ranges it may be clearer to define enum's for the start and end of ranges as applicable eg.
> 
> enum {
>   SAME_FRAME_START = 0,
>   SAME_FRAME_END = 63,
>   SAME_LOCALS_1_STACK_ITEM_FRAME_START = 64,
>   SAME_LOCALS_1_STACK_ITEM_FRAME_END = 127,
>   RESERVED_START = 128,
>   RESERVED_END = 246,
>   SAME_LOCALS_1_STACK_ITEM_EXTENDED = 247,
>   CHOP_FRAME_START = 248,
>   CHOP_FRAME_END = 250,
>   SAME_FRAME_EXTENDED = 251,
>   APPEND_FRAME_START = 252,
>   APPEND_FRAME_END = 254,
>   FULL_FRAME = 255
> }
> 
> and then adjust the code usage as appropriate e.g.
> 
> if (frame_type <= SAME_FRAME_END) {
> ...
> if (frame_type <= SAME_LOCALS_1_STACK_ITEM_FRAME_END) {
>   if (_first) {
>     offset = frame_type - SAME_LOCALS_1_STACK_ITEM_FRAME_START;
> ...
> 
> What do you think?

I wasn't really up for a big rewrite but having the complete set of names would be really good.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25870#discussion_r2158789990