RE: [PATCH] aarch64: Fix -march=native when -mtune is used [PR124629]

> -----Original Message-----
> From: Alice Carlotti <[email protected]>
> Sent: 07 August 2026 18:19
> To: [email protected]
> Cc: Richard Earnshaw <[email protected]>; Tamar Christina
> <[email protected]>; Kyrylo Tkachov <[email protected]>; Alex
> Coplan <[email protected]>; Andrew Pinski
> <[email protected]>; Wilco Dijkstra
> <[email protected]>; Cutie Deng <[email protected]>
> Subject: [PATCH] aarch64: Fix -march=native when -mtune is used
> [PR124629]
> 
> Handling of -march=native for recognised cores was broken by
> r13-2937-g00c22ba69d8e73, which added "V" to ARCH_IDENT values and
> filtered it out in some locations.  This causes a lookup by stringified
> ARCH_IDENT values to fail.  If no -mtune or -mcpu option is used, then
> we avoid this bug by upgrading -march=native to -mcpu=native.
> 
> Fix this by removing the '+ 1' string offset, so that the ident strings
> match again.  It would be marginally more efficient to use enum values
> here, but I've stuck with this simpler fix instead.
> 
> 
> This is the alternative fix I suggested in my review of Cutie Deng's patch [1],
> with an added test case.
> 
> Ok for master and backport to all open branches?

OK with a minor nit below.  OK for branches too but give it some time on trunk.

> 
> [1] https://gcc.gnu.org/pipermail/gcc-patches/2026-March/711748.html
> 
> 
> gcc/ChangeLog:
> 
> 	PR target/124629
> 	* config/aarch64/driver-aarch64.cc (AARCH64_ARCH):
> 	Don't skip first character of #ARCH_IDENT.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR target/124629
> 	* gcc.target/aarch64/cpunative/info_36: New test file.
> 	* gcc.target/aarch64/cpunative/native_cpu_36.c: New test.
> 
> 
> diff --git a/gcc/config/aarch64/driver-aarch64.cc
> b/gcc/config/aarch64/driver-aarch64.cc
> index
> 278f26c92194801739c57862de097a3093487de2..300cdceca63c3c984406
> 37258bd85a212b300952 100644
> --- a/gcc/config/aarch64/driver-aarch64.cc
> +++ b/gcc/config/aarch64/driver-aarch64.cc
> @@ -81,7 +81,7 @@ struct aarch64_arch_driver_info
> 
>  /* Skip the leading "V" in the architecture name.  */

This comment is no longer accurate.

Thanks,
Tamar

>  #define AARCH64_ARCH(NAME, CORE, ARCH_IDENT, ARCH_REV, FLAGS) \
> -  { #ARCH_IDENT + 1, NAME, feature_deps::ARCH_IDENT ().enable },
> +  { #ARCH_IDENT, NAME, feature_deps::ARCH_IDENT ().enable },
> 
>  static constexpr const aarch64_arch_driver_info aarch64_arches[] =
>  {
> diff --git a/gcc/testsuite/gcc.target/aarch64/cpunative/info_36
> b/gcc/testsuite/gcc.target/aarch64/cpunative/info_36
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..620340fdfaeb8d0bdf9
> 43a5563603bc04ab88ce4
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/cpunative/info_36
> @@ -0,0 +1,9 @@
> +processor	: 0
> +BogoMIPS	: 100.00
> +Features	: fp asimd evtstrm aes pmull sha1 sha2 crc32 asimddp sve
> sve2 fphp asimdhp fcma
> +CPU implementer	: 0x41
> +CPU architecture: 8
> +CPU variant	: 0x0
> +CPU part	: 0xd08
> +CPU revision	: 2
> +
> diff --git a/gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_36.c
> b/gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_36.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..04af5b04ba5f9c2193f
> d4725ad3aa67d185461ea
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/cpunative/native_cpu_36.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile { target { { aarch64*-*-linux*} && native } } } */
> +/* { dg-set-compiler-env-var GCC_CPUINFO
> "$srcdir/gcc.target/aarch64/cpunative/info_36" } */
> +/* { dg-additional-options "-march=native -mtune=cortex-a34" } */
> +
> +int main()
> +{
> +  return 0;
> +}
> +
> +/* { dg-final { scan-assembler {\.arch armv8-
> a\+dotprod\+crc\+crypto\+sve2\n} } } */