RE: CRC32C Parallel Computation Optimization on ARM

On Date: Fri, 10 Nov 2023 10:36:08AM -0600, Nathan Bossart wrote:

>-# all versions of pg_crc32c_armv8.o need CFLAGS_CRC
>-pg_crc32c_armv8.o: CFLAGS+=$(CFLAGS_CRC)
>-pg_crc32c_armv8_shlib.o: CFLAGS+=$(CFLAGS_CRC)
>-pg_crc32c_armv8_srv.o: CFLAGS+=$(CFLAGS_CRC)
>
>Why are these lines deleted?
>
>- ['pg_crc32c_armv8', 'USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK', 'crc'],
>+ ['pg_crc32c_armv8', 'USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK'],
>
>What is the purpose of this change?

Because I added `__attribute__((target("+crc+crypto")))` before the functions that require crc extension and crypto extension, so they are removed here.

>+__attribute__((target("+crc+crypto")))
>
>I'm not sure we can assume that all compilers will understand this, and I'm
>not sure we need it.

CFLAGS_CRC is "-march=armv8-a+crc". Generally, if -march is supported, __attribute__ is also supported.
In addition, I am not sure about the source file pg_crc32c_armv8.c, if CFLAGS_CRC and CFLAGS_CRYPTO are needed at the same time, how should it be expressed in the makefile?

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