From: Jan Hubicka <hubicka@ucw.cz>
To: Alexander Monakov <amonakov@ispras.ru>
Cc: Jan Hubicka <hubicka@ucw.cz>,
gcc-patches@gcc.gnu.org, Uros Bizjak <ubizjak@gmail.com>,
Rich Felker <dalias@libc.org>
Subject: Re: [PATCH i386] Extend sibcall peepholes to allow source in %eax
Date: Mon, 11 May 2015 18:00:00 -0000 [thread overview]
Message-ID: <20150511180038.GA22960@kam.mff.cuni.cz> (raw)
In-Reply-To: <alpine.LNX.2.11.1505112039590.22867@monopod.intra.ispras.ru>
> On Sun, 10 May 2015, Jan Hubicka wrote:
>
> > > On i386, peepholes that transform memory load and register-indirect jump into
> > > memory-indirect jump are overly restrictive in that they don't allow combining
> > > when the jump target is loaded into %eax, and the called function returns a
> > > value (also in %eax, so it's not dead after the call). Fix this by checking
> > > for same source and output register operands separately.
> > >
> > > OK?
> > > * config/i386/i386.md (sibcall_value_memory): Extend peepholes to
> > > allow memory address in %eax.
> > > (sibcall_value_pop_memory): Likewise.
> >
> > Why do we need the check for liveness after all? There is SIBLING_CALL_P
> > (peep2_next_insn (1)) so we know that the function terminates by the call
> > and there are no other uses of the value.
>
> Indeed. Uros, the peep2_reg_dead_p check was added by your patch as svn
> revision 211776, git commit e51f8b8fed. Would you agree that the check is not
> necessary for sibcalls as Honza explains? Would you approve a patch that
> removes it in the sibcall peepholes I modify in the patch under discussion?
>
> > Don't we however need to check that operands[0] is not used by the call_insn as
> > parameter of the call? I.e. something like
> >
> > void
> > test(void (*callback ()))
> > {
> > callback(callback);
> > }
>
> You need a pointer-to-pointer-to-function to trigger the peephole. Something
> like this:
>
> void foo()
> {
> void (**bar)(void*);
> asm("":"=r"(bar));
> (*bar)(*bar);
> }
>
> > I think instead of peep2_reg_dead_p we want to check that the parameter is not in
> > CALL_INSN_FUNCTION_USAGE of the sibcall..
>
> Playing with the above testcase I can't induce failure. It seems today GCC
> won't allocate the same register as callee address and one of the arguments.
> Do you want me to implement such a check anyway?
Hmm, only way I can trigger same register is:
void foo()
{
void (**bar)(void*);
asm("":"=r"(bar));
register void (*var)(void *) asm("%eax");
var=*bar;
asm("":"+r"(var));
var(var);
}
removing the second asm makes CSE to forward propagae the memory operand
to call that makes the call different from the register variable.
Still I would check for that, but this is more Uros' area.
Honza
next prev parent reply other threads:[~2015-05-11 18:00 UTC|newest]
Thread overview: 106+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-04 16:38 PIC calls without PLT, generic implementation Alexander Monakov
2015-05-04 16:38 ` [PATCH i386] Extend sibcall peepholes to allow source in %eax Alexander Monakov
2015-05-10 16:54 ` Jan Hubicka
2015-05-11 17:50 ` Alexander Monakov
2015-05-11 18:00 ` Jan Hubicka [this message]
2015-05-11 19:46 ` Uros Bizjak
2015-05-11 19:48 ` Jeff Law
2015-05-11 20:16 ` Jan Hubicka
2015-05-13 19:05 ` Alexander Monakov
2015-05-13 20:04 ` Jan Hubicka
2015-05-14 17:36 ` Alexander Monakov
2015-05-04 16:38 ` [PATCH i386] Move CLOBBERED_REGS earlier in register class list Alexander Monakov
2015-05-10 16:44 ` Jan Hubicka
2015-05-10 17:51 ` Uros Bizjak
2015-05-10 18:09 ` Uros Bizjak
2015-05-11 16:26 ` Alexander Monakov
2015-05-11 16:30 ` Uros Bizjak
2015-05-04 16:38 ` [PATCH i386] PR65753: allow PIC tail calls via function pointers Alexander Monakov
2015-05-10 16:37 ` Jan Hubicka
2015-05-11 16:11 ` Alexander Monakov
2015-05-04 16:38 ` [RFC PATCH] ira: accept loads via argp rtx in validate_equiv_mem Alexander Monakov
2015-05-04 17:37 ` Jeff Law
2015-05-04 16:38 ` [PATCH] Expand PIC calls without PLT with -fno-plt Alexander Monakov
2015-05-04 17:34 ` Jeff Law
2015-05-04 17:40 ` Jakub Jelinek
2015-05-04 17:42 ` Jeff Law
2015-05-06 3:08 ` Rich Felker
2015-05-10 17:07 ` Jan Hubicka
2015-05-06 15:25 ` Alexander Monakov
2015-05-06 15:46 ` Jakub Jelinek
2015-05-06 15:55 ` Jeff Law
2015-05-06 16:44 ` Alexander Monakov
2015-05-06 17:35 ` Rich Felker
2015-05-06 18:26 ` H.J. Lu
2015-05-06 18:37 ` Rich Felker
2015-05-06 18:45 ` H.J. Lu
2015-05-06 19:01 ` Rich Felker
2015-05-06 19:05 ` H.J. Lu
2015-05-06 19:18 ` Rich Felker
2015-05-06 19:24 ` H.J. Lu
2015-05-11 11:48 ` Michael Matz
2015-05-11 14:20 ` Rich Felker
2015-05-07 18:22 ` Jeff Law
2015-05-07 19:13 ` H.J. Lu
2015-05-10 16:59 ` Jan Hubicka
2015-05-11 20:36 ` Jeff Law
2015-05-11 20:55 ` H.J. Lu
2015-05-11 22:13 ` Jan Hubicka
2015-06-22 15:52 ` Jiong Wang
2015-06-22 18:18 ` Alexander Monakov
2015-06-23 8:41 ` Ramana Radhakrishnan
2015-06-23 10:43 ` Alexander Monakov
2015-06-23 13:28 ` Jeff Law
2015-07-16 10:37 ` [AArch64] Tighten direct call pattern to repair -fno-plt Jiong Wang
2015-07-16 10:47 ` Alexander Monakov
2015-07-16 10:48 ` Jiong Wang
2015-07-21 12:52 ` [AArch64][sibcall]Tighten " Jiong Wang
2015-08-04 9:50 ` James Greenhalgh
2015-08-06 16:18 ` [COMMITTED][AArch64][sibcall]Tighten " Jiong Wang
2015-08-07 8:22 ` James Greenhalgh
2015-08-07 13:28 ` Jiong Wang
2015-08-04 9:50 ` [AArch64] Tighten " James Greenhalgh
2015-08-06 16:16 ` [COMMITTED][AArch64] " Jiong Wang
2015-05-04 16:38 ` [PATCH i386] Allow sibcalls in no-PLT PIC Alexander Monakov
2015-05-15 16:37 ` Alexander Monakov
2015-05-15 16:48 ` H.J. Lu
2015-05-15 20:08 ` Jan Hubicka
2015-05-15 20:23 ` H.J. Lu
2015-05-15 20:35 ` Rich Felker
2015-05-15 20:37 ` H.J. Lu
2015-05-15 20:45 ` Rich Felker
2015-05-15 22:16 ` H.J. Lu
2015-05-15 23:14 ` Jan Hubicka
2015-05-15 23:30 ` H.J. Lu
2015-05-15 23:35 ` H.J. Lu
2015-05-15 23:44 ` H.J. Lu
2015-05-16 0:18 ` Rich Felker
2015-05-16 14:33 ` H.J. Lu
2015-05-16 19:03 ` H.J. Lu
2015-05-16 19:32 ` Rich Felker
2015-05-16 23:23 ` H.J. Lu
2015-05-15 23:49 ` Rich Felker
2015-05-19 14:48 ` Michael Matz
2015-05-19 15:11 ` Jeff Law
2015-05-19 16:03 ` Michael Matz
2015-05-19 19:11 ` Rich Felker
2015-05-19 18:08 ` Rich Felker
2015-05-19 19:03 ` Richard Henderson
2015-05-19 19:10 ` H.J. Lu
2015-05-19 19:17 ` Richard Henderson
2015-05-19 19:20 ` H.J. Lu
2015-05-19 19:54 ` Richard Henderson
2015-05-19 20:27 ` Rich Felker
2015-05-19 20:44 ` H.J. Lu
2015-05-19 21:28 ` Rich Felker
2015-05-20 0:52 ` H.J. Lu
2015-05-20 1:09 ` Rich Felker
2015-05-22 19:32 ` Richard Henderson
2015-05-19 19:48 ` Rich Felker
2015-05-19 20:16 ` Richard Henderson
2015-05-20 12:13 ` Michael Matz
2015-05-20 12:40 ` H.J. Lu
2015-05-20 14:17 ` Rich Felker
2015-05-20 14:33 ` Michael Matz
2015-05-18 18:25 ` Alexander Monakov
2015-05-18 19:03 ` Jan Hubicka
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