diff mbox series

fix PowerPC < 7 w/ Altivec not to default to power7

Message ID 20240308.123342.1112119677226246836.rene@exactcode.de
State New
Headers show
Series fix PowerPC < 7 w/ Altivec not to default to power7 | expand

Commit Message

Rene Rebe March 8, 2024, 11:33 a.m. UTC 
This might not be the best timing -short before a major release-,
however, Sam just commented on the bug I filled years ago [1], so here
we go:

Glibc uses .machine to determine assembler optimizations to use.
However, since reworking the rs6000 .machine output selection in
commit e154242724b084380e3221df7c08fcdbd8460674 22 May 2019, G5 as
well as Cell, and even power4 w/ -maltivec currently resulted in
power7. Mask _ALTIVEC away as the .machine selection already did for
GFX and GPOPT.

powerpc64-t2-linux-gnu-gcc  test.c -S -o - -mcpu=G5
	.file	"test.c"
	.machine power7
	.abiversion 2
	.section	".text"
	.ident	"GCC: (GNU) 10.2.0"
	.section	.note.GNU-stack,"",@progbits

We ship this in T2/Linux [2] since 2020 and it is tested on G5, Cell
and Power8.

Signed-of-by: René Rebe <rene@exactcode.de>

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97367
[2] https://t2sde.org

Comments

Kewen.Lin March 11, 2024, 3:09 a.m. UTC | #1 
Hi,

on 2024/3/8 19:33, Rene Rebe wrote:
> This might not be the best timing -short before a major release-,
> however, Sam just commented on the bug I filled years ago [1], so here
> we go:
> 
> Glibc uses .machine to determine assembler optimizations to use.
> However, since reworking the rs6000 .machine output selection in
> commit e154242724b084380e3221df7c08fcdbd8460674 22 May 2019, G5 as
> well as Cell, and even power4 w/ -maltivec currently resulted in
> power7. Mask _ALTIVEC away as the .machine selection already did for
> GFX and GPOPT.

Thanks for fixing, this fix looks reasonable to me, OPTION_MASK_ALTIVEC
is a part of POWERPC_7400_MASK so any specified cpu type which has this
POWERPC_7400_MASK by default and isn't handled early in function
rs6000_machine_from_flags can suffer from this issue.

> 
> powerpc64-t2-linux-gnu-gcc  test.c -S -o - -mcpu=G5
> 	.file	"test.c"
> 	.machine power7
> 	.abiversion 2
> 	.section	".text"
> 	.ident	"GCC: (GNU) 10.2.0"
> 	.section	.note.GNU-stack,"",@progbits
> 

Nit: Could you also add one test case for this?

btw, -mdejagnu-cpu=G5 can force the cpu type in dg-options.

> We ship this in T2/Linux [2] since 2020 and it is tested on G5, Cell
> and Power8.
> 
> Signed-of-by: René Rebe <rene@exactcode.de>
> 
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97367
> [2] https://t2sde.org
> 
> --- gcc-11.1.0-RC-20210423/gcc/config/rs6000/rs6000.cc.vanilla	2021-04-25 22:57:16.964223106 +0200
> +++ gcc-11.1.0-RC-20210423/gcc/config/rs6000/rs6000.cc	2021-04-25 22:57:27.193223841 +0200
> @@ -5765,7 +5765,7 @@
>    HOST_WIDE_INT flags = rs6000_isa_flags;
>  
>    /* Disable the flags that should never influence the .machine selection.  */
> -  flags &= ~(OPTION_MASK_PPC_GFXOPT | OPTION_MASK_PPC_GPOPT | OPTION_MASK_ISEL);
> +  flags &= ~(OPTION_MASK_PPC_GFXOPT | OPTION_MASK_PPC_GPOPT | OPTION_MASK_ALTIVEC | OPTION_MASK_ISEL);

Nit: This line is too long and needs re-format.

BR,
Kewen

>  
>    if ((flags & (ISA_3_1_MASKS_SERVER & ~ISA_3_0_MASKS_SERVER)) != 0)
>      return "power10";
>
diff mbox series

Patch

--- gcc-11.1.0-RC-20210423/gcc/config/rs6000/rs6000.cc.vanilla	2021-04-25 22:57:16.964223106 +0200
+++ gcc-11.1.0-RC-20210423/gcc/config/rs6000/rs6000.cc	2021-04-25 22:57:27.193223841 +0200
@@ -5765,7 +5765,7 @@ 
   HOST_WIDE_INT flags = rs6000_isa_flags;
 
   /* Disable the flags that should never influence the .machine selection.  */
-  flags &= ~(OPTION_MASK_PPC_GFXOPT | OPTION_MASK_PPC_GPOPT | OPTION_MASK_ISEL);
+  flags &= ~(OPTION_MASK_PPC_GFXOPT | OPTION_MASK_PPC_GPOPT | OPTION_MASK_ALTIVEC | OPTION_MASK_ISEL);
 
   if ((flags & (ISA_3_1_MASKS_SERVER & ~ISA_3_0_MASKS_SERVER)) != 0)
     return "power10";