From: Hongtao Liu <crazylht@gmail.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: liuhongt <hongtao.liu@intel.com>,
Jakub Jelinek <jakub@redhat.com>,
Richard Sandiford <richard.sandiford@arm.com>,
GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH 1/2] CALL_INSN may not be a real function call.
Date: Tue, 6 Jul 2021 09:37:12 +0800 [thread overview]
Message-ID: <CAMZc-bxu8oiAFK0H7LNB-zCxMqARyF+uh+L6bpk5P5G_sSFU+A@mail.gmail.com> (raw)
In-Reply-To: <20210705233008.GJ1583@gate.crashing.org>
On Tue, Jul 6, 2021 at 7:31 AM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> Hi!
>
> I ran into this in shrink-wrap.c today.
>
> On Thu, Jun 03, 2021 at 02:54:07PM +0800, liuhongt via Gcc-patches wrote:
> > Use "used" flag for CALL_INSN to indicate it's a fake call. If it's a
> > fake call, it won't have its own function stack.
>
> Could you document somewhere what a "fake call" *is*? Including what
> that means to RTL, how this is expected to be used, etc.? In rtl.h is
fake call is used for TARGET_INSN_CALLEE_ABI, i'll add comments for
#define FAKE_CALL_P(RTX) in rtl.h
> fine with me, but as it is, no one can know when to use this. What does
> "its own function stack" mean in the description here? You can only put
> FAKE_CALL on functions that do not have a stack frame? But that is
> never true on x86, so that cannot be it, unless there isn't a call
> instruction at all? But then, why use an RTL call insn for this?
>
> Other targets simply do not use an RTL "call" when they want to hide
> such an instruction, why can't you do that here, wouldn't that work much
> better? There are many more insns that you may want to hide. The
> traditional solution is to use unspecs, which very directly hides all
> details.
It's explained here,
> >> Yeah. Initially clobber_high seemed like the best appraoch for
> >> handling the tlsdesc thing, but in practice it was too difficult
> >> to shoe-horn the concept in after the fact, when so much rtl
> >> infrastructure wasn't prepared to deal with it. The old support
> >> didn't handle all cases and passes correctly, and handled others
> >> suboptimally.
> >>
> >> I think it would be worth using the same approach as
> >> https://gcc.gnu.org/legacy-ml/gcc-patches/2019-09/msg01466.html for
> >> vzeroupper: represent the instructions as call_insns in which the
> >> call has a special vzeroupper ABI. I think that's likely to lead
> >> to better code than clobber_high would (or at least, it did for tlsdesc).
refer to [1] for more details
[1] https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570265.html
>
>
> Segher
--
BR,
Hongtao
next prev parent reply other threads:[~2021-07-06 1:32 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-13 9:23 [PATCH] [i386] Fix _mm256_zeroupper to notify LRA that vzeroupper will kill sse registers. [PR target/82735] Hongtao Liu
2021-05-13 9:40 ` Uros Bizjak
2021-05-13 9:43 ` Uros Bizjak
2021-05-13 9:54 ` Jakub Jelinek
2021-05-13 11:32 ` Richard Sandiford
2021-05-13 11:37 ` Jakub Jelinek
2021-05-13 11:52 ` Richard Sandiford
2021-05-14 2:27 ` Hongtao Liu
2021-05-17 8:44 ` Hongtao Liu
2021-05-17 9:56 ` Richard Sandiford
2021-05-18 13:12 ` Hongtao Liu
2021-05-18 15:18 ` Richard Sandiford
2021-05-25 6:04 ` Hongtao Liu
2021-05-25 6:30 ` Hongtao Liu
2021-05-27 5:07 ` Hongtao Liu
2021-05-27 7:05 ` Uros Bizjak
2021-06-01 2:24 ` Hongtao Liu
2021-06-03 6:54 ` [PATCH 1/2] CALL_INSN may not be a real function call liuhongt
2021-06-03 6:54 ` [PATCH 2/2] Fix _mm256_zeroupper by representing the instructions as call_insns in which the call has a special vzeroupper ABI liuhongt
2021-06-04 2:56 ` Hongtao Liu
2021-06-04 6:26 ` Uros Bizjak
2021-06-04 6:34 ` Hongtao Liu
2021-06-07 19:04 ` [PATCH] x86: Don't compile pr82735-[345].c for x32 H.J. Lu
2021-06-04 2:55 ` [PATCH 1/2] CALL_INSN may not be a real function call Hongtao Liu
2021-06-04 7:50 ` Jakub Jelinek
2021-07-05 23:30 ` Segher Boessenkool
2021-07-06 0:03 ` Jeff Law
2021-07-06 1:49 ` Hongtao Liu
2021-07-07 14:55 ` Segher Boessenkool
2021-07-07 17:56 ` Jeff Law
2021-07-06 1:37 ` Hongtao Liu [this message]
2021-07-07 2:44 ` Hongtao Liu
2021-07-07 8:15 ` Richard Biener
2021-07-07 14:52 ` Segher Boessenkool
2021-07-07 15:23 ` Hongtao Liu
2021-07-07 23:42 ` Segher Boessenkool
2021-07-08 4:14 ` Hongtao Liu
2021-07-07 15:32 ` Hongtao Liu
2021-07-07 23:54 ` Segher Boessenkool
2021-07-09 7:20 ` Hongtao Liu
2021-07-07 15:52 ` Hongtao Liu
2021-05-27 7:20 ` [PATCH] [i386] Fix _mm256_zeroupper to notify LRA that vzeroupper will kill sse registers. [PR target/82735] Jakub Jelinek
2021-05-27 10:50 ` Richard Sandiford
2021-06-01 2:22 ` Hongtao Liu
2021-06-01 2:25 ` Hongtao Liu
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