patch to fix PR57468

patch to fix PR57468

[Vladimir Makarov]

The following patch fixes

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57468

The patch actually restore the LRA behaviour for x86/x86-64 before rev. 
199298.  The revision was added for PPC SDmode value correct 
generation.  So it is really needed for PPC64 and badly hurts x86/x86-64 
performance (by doing secondary memory reloads when one pseudo is spilled).

The patch was successfully bootstrapped and tested on x86/x86-64 (with 
patch for pr57459).

   Although the change in i386.c, it only concerns to LRA.  So I've 
decided to commit it without x86/x86-64 maintainer approval.  May be I 
am wrong in this situation.  If somebody objects I am ready to revert 
the patch and wait for an approval.

Committed as rev. 199764.

2013-06-06  Vladimir Makarov  <vmakarov@redhat.com>

         PR rtl-optimization/57468
         * config/i386/i386.c (inline_secondary_memory_needed): Ignore
         spilled pseudos.

Re: patch to fix PR57468

[Vladimir Makarov]

On 13-06-06 9:22 PM, David Edelsohn wrote:
>> The patch actually restore the LRA behaviour for x86/x86-64 before rev. 199298. The revision was added for PPC SDmode value correct generation. So it is really needed for PPC64 and badly hurts x86/x86-64 performance (by doing secondary memory reloads when one pseudo is spilled).
>          Should the solution for PPC64 be further limited, even on
> PPC64? Is this going to hurt more normal spilling code on PPC64 that
> does not have the strange restrictions of SDmode?
>
>
   No, it does not hurt ppc performance.  In ppc case, it works the same 
way as reload does (and only for SDmode values).  I also found LRA 
generates a better code for SDmode than reload.  I did not figure out 
why reload pass uses secondary memory when one pseudo is spilled for ppc 
and does not use this for x86/x86-64 although both targets report 
necessity of secondary memory in case when one pseudo is spilled.  It 
requires a lot of time but I should probably still do this.

   I hope that Mike checks performance of LRA as I have no hardware to 
do this.  If he finds any performance degradation, I look at it.

Re: patch to fix PR57468

[David Edelsohn]

> The patch actually restore the LRA behaviour for x86/x86-64 before rev. 199298. The revision was added for PPC SDmode value correct generation. So it is really needed for PPC64 and badly hurts x86/x86-64 performance (by doing secondary memory reloads when one pseudo is spilled).

        Should the solution for PPC64 be further limited, even on
PPC64? Is this going to hurt more normal spilling code on PPC64 that
does not have the strange restrictions of SDmode?

Thanks, David