Re: [PATCH] Add loongarch native checksum implementation.

Updated the patch based on the comments.

On 2023/6/15 18:30, John Naylor wrote:
>
> On Wed, Jun 14, 2023 at 9:20 AM YANG Xudong <yangxudong(at)ymatrix(dot)cn
> <mailto:yangxudong(at)ymatrix(dot)cn>> wrote:
> >
> > Attached a new patch with fixes based on the comment below.
>
> Note: It's helpful to pass "-v" to git format-patch, to have different
> versions.
>

Added v2

> > > For x86 and Arm, if it fails to link without an -march flag, we allow
> > > for a runtime check. The flags "-march=armv8-a+crc" and "-msse4.2" are
> > > for instructions not found on all platforms. The patch also checks both
> > > ways, and each one results in "Use LoongArch CRC instruction
> > > unconditionally". The -march flag here is general, not specific. In
> > > other words, if this only runs inside "+elif host_cpu ==
> 'loongarch64'",
> > > why do we need both with -march and without?
> > >
> >
> > Removed the elif branch.
>
> Okay, since we've confirmed that no arch flag is necessary, some other
> places can be simplified:
>
> --- a/src/port/Makefile
> +++ b/src/port/Makefile
> @@ -98,6 +98,11 @@ pg_crc32c_armv8.o: CFLAGS+=$(CFLAGS_CRC)
>  pg_crc32c_armv8_shlib.o: CFLAGS+=$(CFLAGS_CRC)
>  pg_crc32c_armv8_srv.o: CFLAGS+=$(CFLAGS_CRC)
>
> +# all versions of pg_crc32c_loongarch.o need CFLAGS_CRC
> +pg_crc32c_loongarch.o: CFLAGS+=$(CFLAGS_CRC)
> +pg_crc32c_loongarch_shlib.o: CFLAGS+=$(CFLAGS_CRC)
> +pg_crc32c_loongarch_srv.o: CFLAGS+=$(CFLAGS_CRC)
>
> This was copy-and-pasted from platforms that use a runtime check, so
> should be unnecessary.
>

Removed these lines.

> +# If the intrinsics are supported, sets pgac_loongarch_crc32c_intrinsics,
> +# and CFLAGS_CRC.
>
> +# Check if __builtin_loongarch_crcc_* intrinsics can be used
> +# with the default compiler flags.
> +# CFLAGS_CRC is set if the extra flag is required.
>
> Same here -- it seems we don't need to set CFLAGS_CRC at all. Can you
> confirm?
>

We don't need to set CFLAGS_CRC as commented. I have updated the
configure script to make it align with the logic in meson build script.

> > > Also, I don't have a Loongarch machine for testing. Could you show that
> > > the instructions are found in the binary, maybe using objdump and grep?
> > > Or a performance test?
> > >
> >
> > The output of the objdump command `objdump -dS
> > ../postgres-build/tmp_install/usr/local/pgsql/bin/postgres  | grep -B 30
> > -A 10 crcc` is attached.
>
> Thanks for confirming.
>
> --
> John Naylor
> EDB: http://www.enterprisedb.com <http://www.enterprisedb.com>