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@ymatrix.cn 
> <mailto:yangxudong@ymatrix.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>