diff mbox

Disable -mbranch-likely for -Os when targetting generic architecture

Message ID B5E67142681B53468FAF6B7C31356562441B05F4@hhmail02.hh.imgtec.org
State New
Headers show

Commit Message

Robert Suchanek Aug. 14, 2015, 12:21 p.m. UTC 
Hi,

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.

Disabling this for generic architecture would therefore be desirable for now.

Ok to apply?

Regards,
Robert

gcc/
	* mips.c (mips_option_override): Enable branch likely for non-generic
	architecture.
---
 gcc/config/mips/mips.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Richard Sandiford Aug. 20, 2015, 8:09 p.m. UTC | #1 
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.

Anything that does string ops on the architecture is suspicious :-)

Thanks,
Richard
Matthew Fortune Aug. 20, 2015, 9:42 p.m. UTC | #2 
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.

Thanks,
Matthew
diff mbox

Patch

diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index a9829bd..68def06 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -19564,7 +19564,7 @@  mips_option_override (void)
   if ((target_flags_explicit & MASK_BRANCHLIKELY) == 0)
     {
       if (ISA_HAS_BRANCHLIKELY
-	  && (optimize_size
+	  && ((optimize_size && strncmp (mips_arch_info->name, "mips", 4) != 0)
 	      || (mips_tune_info->tune_flags & PTF_AVOID_BRANCHLIKELY) == 0))
 	target_flags |= MASK_BRANCHLIKELY;
       else