[PATCH] Make mempcpy more optimal (PR middle-end/70140).

[Martin Liška]

On 08/01/2017 09:50 PM, Jakub Jelinek wrote:
> On Thu, Jul 20, 2017 at 08:59:29AM +0200, Martin Liška wrote:
>> Hello.
>>
>> Following patch does sharing of expansion for mem{p,}cpy and also strpcy (with a known constant as source)
>> so that we use same type of expansion (direct insns emission, direct emission with a loop instruction and
>> library call). As mentioned in the PR, glibc does not provide an optimized version for majority of targets.
>>
>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
> 
> This broke e.g.
> FAIL: gcc.dg/20050503-1.c scan-assembler-not call
> on i686-linux, the result is significantly worse.
> Also, while perhaps majority of targets don't provide optimized version,
> some targets do, including i?86/x86_64, and if the memcpy would be expanded
> as a call, it is much better to just emit mempcpy call instead.
> Just look at the testcase, because of this misoptimization we suddenly can't
> use a tail call.
> 
> 	Jakub
> 

I see. That said, should I introduce some target hook that will tell whether to expand to
'return memcpy(dst, src,l) + dst;' or call library mempcpy routine?

Martin