Re: [PATCH] Add loongarch native checksum implementation.

On Wed, Jun 14, 2023 at 9:20 AM YANG Xudong <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.

> > 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.

+# 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?

> > 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