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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/95622] [11 Regression] force_output flag on a variable prevents optimization / regresses c-c++-common/goacc/kernels-alias-ipa-pta{-2,-4,}.c
Date: Fri, 12 Jun 2020 13:10:08 +0000 [thread overview]
Message-ID: <bug-95622-4-JRNRMLvpcw@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-95622-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95622
--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> ---
I think there are three related issues here:
(a) force_output = 1 prevents at least one optimization
(b) If not using force_output = 1, we need to find another way to
tell the compiler that the variable is actually needed – even if
unused. (cf. comment 1)
(c) There are missed optimizations related to offloading – both
before streaming-out the offload table and afterward.
* * *
(See also PR 92029 for another test case fixed – but I think we cannot learn
much from that one as there the optimization happens before the stream out.)
(In reply to Thomas Schwinge from comment #2)
> We'll need to analyze if we need to restore that functionality now, or if
> it's OK to lose that optimization.
Fixing "now" is only possible by reverting the patch. But given that the patch
fixes a wrong code generation (link errors or ICE) and comes after the first
optimizations have been done (before LTO streamout), I would not undo it. –
Hence: not fixing now but the more optimizations the better :-)
[In particular, my impression is that artificial, read-only static variables do
not need to be linked between host and device as one cannot really take their
address and they cannot be updated or changed.]
next prev parent reply other threads:[~2020-06-12 13:10 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 9:08 [Bug middle-end/95622] New: force_output flag on a variable prevents optimization / regresses c-c++-common/goacc/kernels-alias-ipa-pta-2.c burnus at gcc dot gnu.org
2020-06-10 9:18 ` [Bug middle-end/95622] " jakub at gcc dot gnu.org
2020-06-12 10:58 ` [Bug middle-end/95622] [11 Regression] force_output flag on a variable prevents optimization / regresses c-c++-common/goacc/kernels-alias-ipa-pta{-2,-4,}.c tschwinge at gcc dot gnu.org
2020-06-12 13:10 ` burnus at gcc dot gnu.org [this message]
2020-06-16 13:15 ` cvs-commit at gcc dot gnu.org
2020-06-16 13:22 ` cvs-commit at gcc dot gnu.org
2020-07-15 6:56 ` rguenth at gcc dot gnu.org
2020-07-15 7:06 ` burnus at gcc dot gnu.org
2021-01-14 9:00 ` rguenth at gcc dot gnu.org
2021-03-25 18:28 ` burnus at gcc dot gnu.org
2021-03-26 8:21 ` rguenther at suse dot de
2021-04-27 11:39 ` [Bug middle-end/95622] [11/12 " jakub at gcc dot gnu.org
2021-07-28 7:04 ` rguenth at gcc dot gnu.org
2022-04-21 7:48 ` rguenth at gcc dot gnu.org
2023-05-29 10:02 ` [Bug middle-end/95622] [11/12/13/14 " jakub at gcc dot gnu.org
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