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Re: [PATCH] New attribute to create target clones
- From: Jan Hubicka <hubicka at ucw dot cz>
- To: Evgeny Stupachenko <evstupac at gmail dot com>
- Cc: Jan Hubicka <hubicka at ucw dot cz>, Jeff Law <law at redhat dot com>, Bernd Schmidt <bschmidt at redhat dot com>, Bernd Schmidt <bernds_cb1 at t-online dot de>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 9 Oct 2015 22:04:22 +0200
- Subject: Re: [PATCH] New attribute to create target clones
- Authentication-results: sourceware.org; auth=none
- References: <5601C375 dot 5050706 at redhat dot com> <CAOvf_xwUK1k=zx=f7eAWs4xs2J4KBCZGzeom_a5SfdkfF_gqSQ at mail dot gmail dot com> <CAOvf_xy6Kq_AGArurgxYC65K=LMNt6_gXHK15VFsoCd64F+TTA at mail dot gmail dot com> <5616BD37 dot 2000307 at redhat dot com> <20151008192349 dot GB90964 at kam dot mff dot cuni dot cz> <5616C9CA dot 2010702 at redhat dot com> <20151008213644 dot GD5527 at kam dot mff dot cuni dot cz> <5617FD1D dot 9010406 at redhat dot com> <20151009182753 dot GA7750 at kam dot mff dot cuni dot cz> <CAOvf_xyO5_s6ZF56SErj24N8ARbSHEH_nHAKfKFa1uWX+T9xiQ at mail dot gmail dot com>
> On Fri, Oct 9, 2015 at 9:27 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >> >Of course it also depends what you inline into function. You can have
> >> >
> >> >bar() target(-mavx) {fancy avx code}
> >> >foobar() { ...... if (avx) bar();}
> >> >foo() ctarget(-mavx,-mno-avx) {....foobar();....}
>
> "no-" targets are not supported
Why not? I suppose I can use -march=x86_64 in a file compiled with -march=core-avx2 or something like that, too.
>
> >> >
> >> >Now if you compile with -mavx and because ctarget takes effect only after inlining,
> >> >at inlining time the target attributes will match and we can edn up inline bar->foobar->foo.
> >> >After that we multiversion foo and drop AVX flag we will likely get ICE at expansion
> >> >time.
> >> But isn't that avoided by fixing up the call graph so that all calls
> >> to the affected function are going through the dispatcher? Or is
> >> that happening too late?
> >
> > There is dispatcher only for foo that is the root of the callgarph tree.
> > When inlining we compare target attributes for match (in can_inline_edge_p).
> > We do not compare ctarget attributes. Expanding ctarget to target early would
> > avoid need for ctarget handling.
> Currently inlining is disabled for functions with target_clone attribute:
Do you also disable inlining into functions with target_clone?
What I am concerned about is early inliner inlining (say) AVX code into ctarget
function because at early inlining time the target is not applied, yet.
Honza