RE: [PATCH] Disable -mbranch-likely for -Os when targetting generic architecture

["Moore, Catherine" <Catherine_Moore@mentor.com>]

> -----Original Message-----
> From: Robert Suchanek [mailto:Robert.Suchanek@imgtec.com]
> Sent: Friday, September 04, 2015 10:21 AM
> To: Matthew Fortune; Richard Sandiford
> Cc: Moore, Catherine; gcc-patches@gcc.gnu.org
> Subject: RE: [PATCH] Disable -mbranch-likely for -Os when targetting generic
> architecture
> 
> Hi,
> 
> > Richard Sandiford <rdsandiford@googlemail.com> writes:
> > > Robert Suchanek <Robert.Suchanek@imgtec.com> writes:
> > > > The patch below disables generation of the branch likely
> > > > instructions for -
> > Os
> > > > but only for generic architecture.  The branch likely may result
> > > > in some code size reduction but the cost of running the code on R6
> > > > core is
> > significant.
> > >
> > > How about instead splitting PTF_AVOID_BRANCHLIKELY into
> > > PTF_AVOID_BRANCHLIKELY_SPEED and
> PTF_AVOID_BRANCHLIKELY_SIZE?
> > > We could have PTF_AVOID_BRANCHLIKELY_ALWAYS as an OR of the two.
> >
> > This sounds OK and is nicer.
> >
> > > Anything that does string ops on the architecture is suspicious :-)
> >
> > You can blame me for this.  I advocated the string comparison approach
> > as I had to do the same thing in gas IIRC for some feature and
> > couldn't think of anything better to suggest.
> 
> Here is an updated version that use the suggested method. Ok to apply?
> 
> Regards,
> Robert
> 
> gcc/
> 	* config/mips/mips-cpus.def: Replace PTF_AVOID_BRANCHLIKELY
> with
> 	PTF_AVOID_BRANCHLIKELY_ALWAYS for generic architecture and
> with
> 	PTF_AVOID_BRANCHLIKELY_SPEED for others.
> 	(mips2, mips3, mips4): Add PTF_AVOID_BRANCHLIKELY_SIZE to tune
> flags.
> 	* config/mips/mips.c (mips_option_override): Enable the branch
> likely
> 	depending on the tune flags and optimization level.
> 	* config/mips/mips.h (PTF_AVOID_BRANCHLIKELY): Remove.
> 	(PTF_AVOID_BRANCHLIKELY_SPEED): Define.
> 	(PTF_AVOID_BRANCHLIKELY_SIZE): Likewise.
> 	(PTF_AVOID_BRANCHLIKELY_ALWAYS): Likewise.
> ---
>  gcc/config/mips/mips-cpus.def | 56 +++++++++++++++++++++---------------
> -------
>  gcc/config/mips/mips.c        |  6 +++--
>  gcc/config/mips/mips.h        | 20 ++++++++++++----
>  3 files changed, 47 insertions(+), 35 deletions(-)
> 
> a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c index 0e0ecf2..f8775c4
> 100644
> --- a/gcc/config/mips/mips.c
> +++ b/gcc/config/mips/mips.c
> @@ -17916,8 +17916,10 @@ mips_option_override (void)
>    if ((target_flags_explicit & MASK_BRANCHLIKELY) == 0)
>      {
>        if (ISA_HAS_BRANCHLIKELY
> -	  && (optimize_size
> -	      || (mips_tune_info->tune_flags & PTF_AVOID_BRANCHLIKELY)
> == 0))
> +	  && ((optimize_size && (mips_tune_info->tune_flags
> +				 & PTF_AVOID_BRANCHLIKELY_SIZE) == 0)
> +	       || (!optimize_size && (mips_tune_info->tune_flags
> +				      & PTF_AVOID_BRANCHLIKELY_SPEED) ==
> 0)))
>  	target_flags |= MASK_BRANCHLIKELY;
>        else
>  	target_flags &= ~MASK_BRANCHLIKELY;

Should this check be:
Index: mips.c
===================================================================
--- mips.c      (revision 229138)
+++ mips.c      (working copy)
@@ -17758,8 +17758,15 @@
   if ((target_flags_explicit & MASK_BRANCHLIKELY) == 0)
     {
       if (ISA_HAS_BRANCHLIKELY
-         && (optimize_size
-             || (mips_tune_info->tune_flags & PTF_AVOID_BRANCHLIKELY) == 0))
+         && ((optimize_size
+              && (mips_tune_info->tune_flags
+                  & PTF_AVOID_BRANCHLIKELY_SIZE) == 0)
+             || (!optimize_size
+                && optimize > 0
+                && ((mips_tune_info->tune_flags
+                     & PTF_AVOID_BRANCHLIKELY_SPEED) == 0))
+            || (mips_tune_info->tune_flags
+                 & PTF_AVOID_BRANCHLIKELY_ALWAYS) == 0))
        target_flags |= MASK_BRANCHLIKELY;
       else
        target_flags &= ~MASK_BRANCHLIKELY;

Instead?  I don't see a use of PTF_AVOID_BRANCH_ALWAYS in your patch, but it seems like it should be checked.