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* [Bug c++/105937] New: [12] Regression with maybe-uninitialized
@ 2022-06-12 22:12 janisozaur+gcc at gmail dot com
2022-06-12 22:16 ` [Bug tree-optimization/105937] " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: janisozaur+gcc at gmail dot com @ 2022-06-12 22:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105937
Bug ID: 105937
Summary: [12] Regression with maybe-uninitialized
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: janisozaur+gcc at gmail dot com
Target Milestone: ---
Created attachment 53125
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53125&action=edit
Test case extracted from original code
Commit https://gcc.gnu.org/g:6feb628a706e86eb3f303aff388c74bdb29e7381 "Improve
warning suppression for inlined functions [PR98512]. " introduced a regression
when using std::optional.
Ever since that commit, when building optimized code compiler complains:
/home/mijn/workspace/openrct2/src/openrct2/drawing/Drawing.String.cpp: In
function ‘void ttf_process_string_literal(OpenRCT2::IContext*,
std::string_view)’:
/home/mijn/workspace/openrct2/src/openrct2/drawing/Drawing.String.cpp:215:62:
error: ‘*(long unsigned int*)((char*)&ttfRunIndex + offsetof(std::optional<long
unsigned int>,std::optional<long unsigned
int>::<unnamed>.std::_Optional_base<long unsigned int, true,
true>::<unnamed>))’ may be used uninitialized in this function
[-Werror=maybe-uninitialized]
215 | auto len = it.GetIndex() - ttfRunIndex.value();
| ^
gcc -v:
Using built-in specs.
COLLECT_GCC=/home/mijn/workspace/gcc-install-master/bin/c++
COLLECT_LTO_WRAPPER=/home/mijn/workspace/gcc-install-master/libexec/gcc/x86_64-pc-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure
--prefix=/home/mijn/workspace/gcc-install-master --enable-languages=c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20210702 (experimental) (GCC)
Provided an extracted test case for the issue mentioned.
Original code:
https://github.com/OpenRCT2/OpenRCT2/blob/b0ffa9d28e62b862f68a37788931265cb4528835/src/openrct2/drawing/Drawing.String.cpp#L839
Original bug report for OpenRCT2:
https://github.com/OpenRCT2/OpenRCT2/issues/17371
Test case on godbolt: https://godbolt.org/z/6Y3cn1Ks1
c++ -O2 -c -o foo test.cpp -Werror=maybe-uninitialized
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/105937] [12] Regression with maybe-uninitialized
2022-06-12 22:12 [Bug c++/105937] New: [12] Regression with maybe-uninitialized janisozaur+gcc at gmail dot com
@ 2022-06-12 22:16 ` pinskia at gcc dot gnu.org
2022-06-12 22:25 ` [Bug tree-optimization/105937] [12/13 Regression] maybe-uninitialized with std::optional pinskia at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-06-12 22:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105937
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note your example no longer compiles on the trunk of GCC as it requires to add:
#include <stdint.h>
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/105937] [12/13 Regression] maybe-uninitialized with std::optional
2022-06-12 22:12 [Bug c++/105937] New: [12] Regression with maybe-uninitialized janisozaur+gcc at gmail dot com
2022-06-12 22:16 ` [Bug tree-optimization/105937] " pinskia at gcc dot gnu.org
@ 2022-06-12 22:25 ` pinskia at gcc dot gnu.org
2022-10-11 12:06 ` [Bug tree-optimization/105937] [12 " cvs-commit at gcc dot gnu.org
2022-10-11 12:08 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-06-12 22:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105937
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |needs-reduction
Target Milestone|--- |12.2
Summary|[12] Regression with |[12/13 Regression]
|maybe-uninitialized |maybe-uninitialized with
| |std::optional
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
# ttfRunIndex_64 = PHI <ttfRunIndex_6(52), [/app/example.cpp:207:27] 0(30)>
# ttfRunIndex$8_65 = PHI <ttfRunIndex$8_8(52), [/app/example.cpp:207:27]
0(30)>
...
<L17>:
[/app/example.cpp:213:13] if (ttfRunIndex$8_65 != 0)
goto <bb 22>; [33.00%]
else
goto <bb 48>; [67.00%]
...
<bb 22> [local count: 157594832]:
[/app/example.cpp:216:62] len_15 = _20 - ttfRunIndex_64;
...
# ttfRunIndex_6 = PHI <ttfRunIndex_14(D)(26), ttfRunIndex_64(48), _20(21),
ttfRunIndex_64(49)>
# ttfRunIndex$8_8 = PHI <0(26), 0(48), [/app/example.cpp:227:29] 1(21),
1(49)>
So if anything this is both a missed optimization and the maybe uninitialized
predicates is not doing its job correctly.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/105937] [12 Regression] maybe-uninitialized with std::optional
2022-06-12 22:12 [Bug c++/105937] New: [12] Regression with maybe-uninitialized janisozaur+gcc at gmail dot com
2022-06-12 22:16 ` [Bug tree-optimization/105937] " pinskia at gcc dot gnu.org
2022-06-12 22:25 ` [Bug tree-optimization/105937] [12/13 Regression] maybe-uninitialized with std::optional pinskia at gcc dot gnu.org
@ 2022-10-11 12:06 ` cvs-commit at gcc dot gnu.org
2022-10-11 12:08 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-10-11 12:06 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105937
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:627132c9bf9439bf0ac83bb092182055c1e0f3ab
commit r12-8818-g627132c9bf9439bf0ac83bb092182055c1e0f3ab
Author: Richard Biener <rguenther@suse.de>
Date: Fri Aug 19 14:12:52 2022 +0200
tree-optimization/105937 - avoid uninit diagnostics crossing iterations
The following avoids adding PHIs to the worklist for uninit processing
if we reach them following backedges. That confuses predicate analysis
because it assumes the use is happening in the same iteration as the the
definition. For the testcase in the PR the situation is like
void foo (int val)
{
int uninit;
# val = PHI <..> (B)
for (..)
{
if (..)
{
.. = val; (C)
val = uninit;
}
# val = PHI <..> (A)
}
}
and starting from (A) with 'uninit' as argument we arrive at (B)
and from there at (C). Predicate analysis then tries to prove
the predicate of (B) (not the backedge) can prove that the
path from (B) to (C) is unreachable which isn't really what it
necessary - that's what we'd need to do when the preheader
edge of the loop were the edge with the uninitialized def.
So the following makes those cases intentionally false negatives.
PR tree-optimization/105937
* tree-ssa-uninit.cc (find_uninit_use): Do not queue PHIs
on backedges.
(execute_late_warn_uninitialized): Mark backedges.
* g++.dg/uninit-pr105937.C: New testcase.
(cherry picked from commit c77fae1ca796d6ea06d5cd437909905c3d3d771c)
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/105937] [12 Regression] maybe-uninitialized with std::optional
2022-06-12 22:12 [Bug c++/105937] New: [12] Regression with maybe-uninitialized janisozaur+gcc at gmail dot com
` (2 preceding siblings ...)
2022-10-11 12:06 ` [Bug tree-optimization/105937] [12 " cvs-commit at gcc dot gnu.org
@ 2022-10-11 12:08 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-10-11 12:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105937
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Known to fail| |12.2.0
Resolution|--- |FIXED
Known to work| |12.2.1
--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2022-06-12 22:12 [Bug c++/105937] New: [12] Regression with maybe-uninitialized janisozaur+gcc at gmail dot com
2022-06-12 22:16 ` [Bug tree-optimization/105937] " pinskia at gcc dot gnu.org
2022-06-12 22:25 ` [Bug tree-optimization/105937] [12/13 Regression] maybe-uninitialized with std::optional pinskia at gcc dot gnu.org
2022-10-11 12:06 ` [Bug tree-optimization/105937] [12 " cvs-commit at gcc dot gnu.org
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