Re: CRC32C Parallel Computation Optimization on ARM

On Wed, Nov 22, 2023 at 10:16:44AM +0000, Xiang Gao wrote:
> On Date: Fri, 10 Nov 2023 10:36:08AM -0600, Nathan Bossart wrote:
>>+__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.

IMHO we should stick with CFLAGS_CRC for now. If we want to switch to
using __attribute__((target("..."))), I think we should do so in a separate
patch. We are cautious about checking the availability of an attribute
before using it (see c.h), and IIUC we'd need to verify that this works for
all supported compilers that can target ARM before removing CFLAGS_CRC
here.

> 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?

pg_crc32c_armv8.o: CFLAGS += ${CFLAGS_CRC} ${CFLAGS_CRYPTO}

--
Nathan Bossart
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