Re: [PATCH] invoke.texi: Clarify -march=lujiazui

[mayshao-oc <mayshao-oc@zhaoxin.com>]

Hi Jakub:

   I think the modified lujiazui description is what actually 
happens,thanks.

BR
Mayshao
> 
> 
> [这封邮件来自外部发件人 谨防风险]
> 
> Hi!
> 
> Yesterday I was searching which exact CPUs are affected by the PR114576
> wrong-code issue and went from the PTA_* bitmasks in GCC, so arrived
> at the goldmont, goldmont-plus, tremont and lujiazui CPUs (as -march=
> cases which do enable -maes and don't enable -mavx).
> But when double-checking that against the invoke.texi documentation,
> that was true for the first 3, but lujiazui said it supported AVX.
> I was really confused by that, until I found the
> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/604407.html
> explanation.  So, seems the CPUs do have AVX and F16C but -march=lujiazui
> doesn't enable those and even activelly attempts to filter those out from
> the announced CPUID features, in glibc as well as e.g. in libgcc.
> 
> Thus, I think we should document what actually happens, otherwise
> users could assume that
> gcc -march=lujiazui predefines __AVX__ and __F16C__, which it doesn't.
> 
> Tested on x86_64, ok for trunk?
> 
> 2024-04-11  Jakub Jelinek  <jakub@redhat.com>
> 
>          * doc/invoke.texi (lujiazui): Clarify that while the CPUs do support
>          AVX and F16C, -march=lujiazui actually doesn't enable those.
> 
> --- gcc/doc/invoke.texi.jj      2024-04-11 09:26:01.156865894 +0200
> +++ gcc/doc/invoke.texi 2024-04-11 10:47:53.457582922 +0200
> @@ -34696,8 +34696,10 @@ instruction set support.
> 
>   @item lujiazui
>   ZHAOXIN lujiazui CPU with x86-64, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,
> -SSE4.2, AVX, POPCNT, AES, PCLMUL, RDRND, XSAVE, XSAVEOPT, FSGSBASE, CX16,
> -ABM, BMI, BMI2, F16C, FXSR, RDSEED instruction set support.
> +SSE4.2, POPCNT, AES, PCLMUL, RDRND, XSAVE, XSAVEOPT, FSGSBASE, CX16,
> +ABM, BMI, BMI2, FXSR, RDSEED instruction set support.  While the CPUs
> +do support AVX and F16C, these aren't enabled by @code{-march=lujiazui}
> +for performance reasons.
> 
>   @item yongfeng
>   ZHAOXIN yongfeng CPU with x86-64, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,
> 
>          Jakub
>