rfc:jit-ir

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rfc:jit-ir [2023/10/24 09:43] – Updated "Implemenetation" section dmitryrfc:jit-ir [2025/01/17 11:22] (current) – Link to correct merge commits, and fix typos/grammar theodorejb
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 ===== Introduction ===== ===== Introduction =====
-The first version of JIT for PHP was released in PHP-8.0 (https://wiki.php.net/rfc/jit). That time we took a quite simple approach. We are generating native code directly from Zend VM byte code. This approach allowed to deliver JIT in a quite short time, but it also created significant limitations in possible optimizations. Smart optimizations require a more formal and detailed **Intermediate Representation** (IR). The introduction of the AArch64 JIT back-end in PHP-8.1, made the maintenance of JIT a bit more complex, because now we often have to update assembler code in two back-ends.+The first version of JIT for PHP was released in PHP-8.0 (https://wiki.php.net/rfc/jit). That time we took a quite simple approach. We are generating native code directly from Zend VM byte code. This approach allowed to deliver JIT in a quite short time, but it also created significant limitations in possible optimizations. Smart optimizations require a more formal and detailed **Intermediate Representation** (IR). The introduction of the AArch64 JIT back-end in PHP-8.1 made the maintenance of JIT a bit more complex, because now we often have to update assembler code in two back-ends.
    
-A smarter JIT compiler with some Intermediate Representation was planned a long time. The real work was started in January 2022.+A smarter JIT compiler with some Intermediate Representation was planned for a long time, and the real work was started in January 2022.
 This proposal is the result of these 1.75 years of work. This proposal is the result of these 1.75 years of work.
    
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 At the current state the PR doesn't remove the sources of the old JIT implementation. It is possible to switch to the old implementation by configuring PHP with **--disable-opcache-jit-ir**. At the current state the PR doesn't remove the sources of the old JIT implementation. It is possible to switch to the old implementation by configuring PHP with **--disable-opcache-jit-ir**.
  
-JIT is a quite complex subsystem. Its first implementation will likely have bugs, but I am confident that these can be addressed. We have more time to fix potential issues, the sooner this proposal passes, and the patch is merged.+JIT is a quite complex subsystem. Its first implementation will likely have bugs, but I am confident that these can be addressed. We have more time to fix potential issues the sooner this proposal passes, and the patch is merged.
  
-The main goal of a separate IR Framework development is the collaboration with other compiler experts (sharing expertise, contribution, etc.). I'm doing my best to make the IR project interesting outside the PHP world and involve others. In case of success, this will reduce the PHP "bus-factor".+The main goal of a separate IR Framework development is the collaboration with other compiler experts (sharing expertise, contributions, etc.). I'm doing my best to make the IR project interesting outside the PHP world and involve others. In case of success, this will reduce the PHP "bus-factor".
  
 The necessary part of the IR Framework is embedded into the PHP source tree, and won't introduce any new external dependencies. The necessary part of the IR Framework is embedded into the PHP source tree, and won't introduce any new external dependencies.
  
-The details of the IR framework are complex. This [[https://www.researchgate.net/publication/374470404_IR_JIT_Framework_a_base_for_the_next_generation_JIT_for_PHP|presentation]] explains design ideas and makes overview of the most important implementaion details.+The details of the IR framework are complex. This [[https://www.researchgate.net/publication/374470404_IR_JIT_Framework_a_base_for_the_next_generation_JIT_for_PHP|presentation]] explains design ideas and provides an overview of the most important implementation details.
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
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 Because the IR Framework provides more optimizations and has a smarter Register Allocator, the JIT produces a bit faster (5-10%) and smaller code. Because the IR Framework provides more optimizations and has a smarter Register Allocator, the JIT produces a bit faster (5-10%) and smaller code.
  
-This is visible with **bench.php** and **micro_bench.php**. The speed of the real-life applications is not affected.+This is visible with **bench.php** and **micro_bench.php**. The speed of real-life applications is not affected.
  
 The compilation speed of the Tracing JIT is almost the same. The compilation speed of the Function JIT is up to 4 times slower (tested on Wordpress). The compilation speed of the Tracing JIT is almost the same. The compilation speed of the Function JIT is up to 4 times slower (tested on Wordpress).
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 ==== php.ini Defaults ==== ==== php.ini Defaults ====
  
-The PR does not introduce new php.ini detectives or changes any default values.+The PR does not introduce new php.ini directives or change any default values.
  
 It adds few new IR related JIT debugging capabilities that may be enabled through **opcache.jit_debug** directive bits: It adds few new IR related JIT debugging capabilities that may be enabled through **opcache.jit_debug** directive bits:
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 ===== Future Scope ===== ===== Future Scope =====
  
-The usage of IR opens the door for more powerful optimizations. Some of these are going to be PHP independent (e.g.): the planned +The usage of IR opens the door for more powerful optimizations. Some of these are going to be PHP independent (e.g. the planned introduction of new loop optimization passes, improved LOAD/STORE motion and redundancy, and improvements to the code generator).
-introduction of new loop optimization passes, improvement in LOAD/STORE motion and redundancy, improvements to the code generator.+
  
 The other part is PHP specific (for example, we can extend CPU register usage for more instructions). The other part is PHP specific (for example, we can extend CPU register usage for more instructions).
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 Secondary vote: Should we keep the old JIT implementation for a while or remove it right after merge? Secondary vote: Should we keep the old JIT implementation for a while or remove it right after merge?
  
-Note, that old implementation is not going to be tested (by CI) and we can't guarantee its work anyway.+Note, that old implementation is not going to be tested (by CI) and we can't guarantee its functionality anyway.
  
 <doodle title="Remove the old JIT implementation right after merging the new one?" auth="user" voteType="single" closed="true"> <doodle title="Remove the old JIT implementation right after merging the new one?" auth="user" voteType="single" closed="true">
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 ===== Implementation ===== ===== Implementation =====
  
-   - merged into master via 25cb2a40d640b64f8881a894f2247d46a781ef75 +   - merged into master via https://github.com/php/php-src/commit/caf102dfaef1ef4191c76a4502c6b4fef20cba46 
-   - old JIT implementation is removed via be275433d936e41d95b2fd656464bcc4d7138b76+   - old JIT implementation is removed via https://github.com/php/php-src/commit/be275433d936e41d95b2fd656464bcc4d7138b76
  
 ===== References ===== ===== References =====
rfc/jit-ir.txt · Last modified: 2025/01/17 11:22 by theodorejb

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