On Mon, Aug 3, 2020 at 7:44 PM Benjamin Eberlei <kont...@beberlei.de> wrote:
> Hi, > > I am going to pick up a discussion from > https://github.com/php/php-src/pull/5915 about the @@Jit attribute. > > Nikita mentioned he is still not 100% clear what the usecase is for @@Jit > attribute and asked to discuss here. > > The reason is that the default tracing JIT is clever to decide itself when > to JIT or not, better not interfere with that. In case you run the tracing > JIT, only @@Jit("off") has an effect the others @@Jit("tracing") and > @@Jit("function") get ignored. > > Only the trigger mode 4 (attributes) is actually using @@Jit("tracing") > and "function". This trigger mode feels like micro-management for > developers and since it has virtually no spotlight in discussions and blog > posts about the JIT at the moment, we don't know if it brings benefits. > > Maybe for now it would be better to remove docblock / attribute support > for the JIT, and take a new attempt at it in 8.1? That prevents us from > rolling something we regret having to maintain later. > I updated the PR https://github.com/php/php-src/pull/5915 with the following things: - Removed attribute trigger mode for now. - Removed obsolete doc comment trigger mode - Add @@Jit("off") to disable JIT for an op_array or script Open questions: - Are we ok with removing @Jit("on"), @@Jit("tracing") and @@Jit("function") for now to thoroughly discuss best approach for 8.1? - Rename @@Jit to something more specific like @@JitOptions or @@JitHint? - Remove the attribute trigger constant 4, and move tracing JIT to use 4 instead of 5? Outlook: We need to think about what the @@Jit attribute should actually mean in context of the function or tracing JIT. Personally it probably means "Always Jit this function regardless of hot counter or tracing results". I believe we don't need the attributes trigger mode, as everything happens either in context of function or tracing JIT. > greetings > Benjamin >
