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Ventana: Jeff Law – oversight, patch review
External:
Significant design work and theoretical background provided by Philipp Tomsich and Henry Brausen of VRULL
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Updates
- Mariam has posted the CRC optimization work for upstream review. This includes methods to generate CRC using clmul, table lookups for RISC-V. For testing purposes it also supports AArch64 and x86_64's clmul variants as well as the x86_64 crc instruction if the proper polynomial is used.
- Jeff Law has started review work. Expecting to get input from Intel and ARM/Linaro engineers as the implementation includes support for those architectures.
- Simple tests using this code to detect a CRC loop that is compatible with the x86 crc32 instruction and generating the crc32 instruction for such loops show using the crc32 instruction is at least 5X faster than a loop.
- Currently investigating generating aarch64 clmul as there is a bit time to do this as a proof of concept before focusing on the upstreaming effort.
- It had been speculated that this work could generate a "crc" instruction on suitable ISAs if a loop with the right field polynomial were encountered. This has been implemented as a proof of concept on x86
- It has also been speculated that this work could be used to detect clmul idioms outside of a CRC loop. This appears to work by relaxing various aspects of the CRC loop verifier. It is not an area of focus though.
- Minor bugs have been fixed in the implementation as it is prepared for upstreaming. Goal is still integration for gcc-15 in the late spring.
- Implementation done for x86_64 using its clmul. Primary purpose was to show that using clmul, while requiring target specific development, is not a major effort. This is expected to help with the upstreaming effort.
- Code drop from 1/26 integrated into the upstream GCC tester.
- Expectation is to submit code for upstream review in Feb with a goal of integrating for gcc-15 in the late spring.
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