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Re: [PATCH] Avoid some unnecessary set_cfun calls


On Wed, Nov 13, 2013 at 10:49:09AM +0100, Jakub Jelinek wrote:
> Hi!
> void f1 (void) {}
> __attribute__((target ("avx"))) void f2 (void) {}
> __attribute__((target ("avx2"))) void f3 (void) {}
> __attribute__((target ("sse3"))) void f4 (void) {}
> __attribute__((target ("ssse3"))) void f5 (void) {}
> __attribute__((target ("sse4"))) void f6 (void) {}
> takes about 3 seconds to compile at -O2, because set_cfun is terribly
> expensive and there are hundreds of such calls.
> The following patch is just a quick change to avoid some of them:
> execute_function_todo starts with:
>   unsigned int flags = (size_t)data;
>   flags &= ~cfun->last_verified;
>   if (!flags)
>     return;
> and if flags is initially zero, it does nothing.
> Similarly, execute_function_dump has the whole body surrounded by
>   if (dump_file && current_function_decl)
> and thus if dump_file is NULL, there is nothing to do.
> So IMHO in neither case (which happens pretty frequently) we need to
> set_cfun to every function during IPA.
> Also, I wonder if we couldn't defer the expensive ira_init, if the info
> computed by it is used only during RTL optimization passes (haven't verified
> it yet), then supposedly we could just remember using some target hook
> what the last state was when we did ira_init last time, and call ira_init
> again at the start of expansion or so if it is different from the
> last time.

I was wondering whether the expensive parts of set_cfun could only be
run in pass_all_optimizations (and the -Og equivalent) but not when
changing functions in early and IPA passes.


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