Re: patch to fix PR57468

[Vladimir Makarov <vmakarov@redhat.com>]

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.