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* [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher @ 2023-01-19 16:08 vincent-gcc at vinc17 dot net 2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org ` (3 more replies) 0 siblings, 4 replies; 5+ messages in thread From: vincent-gcc at vinc17 dot net @ 2023-01-19 16:08 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467 Bug ID: 108467 Summary: false positive -Wmaybe-uninitialized warning at -O1 or higher Product: gcc Version: 12.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: vincent-gcc at vinc17 dot net Target Milestone: --- Consider the following code, derived from MPFR's sub1sp.c (where the issue occurred since at least GCC 4.9.4 and the warning was silenced with the "sh = sh" trick via an INITIALIZED() macro): extern long emin; extern long emax; int f(void); int g(void) { int sh, rb, sb; if (f()) rb = sb = 0; else { sh = f(); sb = f(); rb = f(); } (0 >= emin && 0 <= emax) || (f(), __builtin_unreachable(), 0); if (rb == 0 && sb == 0) return 0; else return sh; } With gcc-12 (Debian 12.2.0-14) 12.2.0, I get: $ gcc-12 -O2 -Wmaybe-uninitialized -c tst.c tst.c: In function ‘g’: tst.c:23:12: warning: ‘sh’ may be used uninitialized [-Wmaybe-uninitialized] 23 | return sh; | ^~ tst.c:8:7: note: ‘sh’ was declared here 8 | int sh, rb, sb; | ^~ The warning also occurs at -O1 and -O3. It disappears if I slightly modify the code. Note: During the code reduction, I also got the warning, but with a different location. However, the code was more complex, and I've already reported PR108466 about a location issue (where the -Wmaybe-uninitialized is correct). So I haven't reported an additional issue about the location. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher 2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net @ 2023-01-19 16:15 ` pinskia at gcc dot gnu.org 2023-01-20 8:28 ` rguenth at gcc dot gnu.org ` (2 subsequent siblings) 3 siblings, 0 replies; 5+ messages in thread From: pinskia at gcc dot gnu.org @ 2023-01-19 16:15 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Known to fail| |4.1.2 Last reconfirmed| |2023-01-19 Status|UNCONFIRMED |NEW --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- After normalization [USE]: _7 = PHI <0(13), sh_4(8)> is conditional on: ((NOT (_3 == 0)) AND (emax.3_2 >= 0) AND (emin.2_1 <= 0)) _3 = rb_5 | sb_6; if (_3 == 0) Confirmed. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher 2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net 2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org @ 2023-01-20 8:28 ` rguenth at gcc dot gnu.org 2024-06-15 2:07 ` sjames at gcc dot gnu.org 2024-06-15 9:41 ` vincent-gcc at vinc17 dot net 3 siblings, 0 replies; 5+ messages in thread From: rguenth at gcc dot gnu.org @ 2023-01-20 8:28 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467 --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- There's some special code dealing with checking on a conditional set value but that's confused by the two-value guard here. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher 2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net 2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org 2023-01-20 8:28 ` rguenth at gcc dot gnu.org @ 2024-06-15 2:07 ` sjames at gcc dot gnu.org 2024-06-15 9:41 ` vincent-gcc at vinc17 dot net 3 siblings, 0 replies; 5+ messages in thread From: sjames at gcc dot gnu.org @ 2024-06-15 2:07 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467 Sam James <sjames at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |sjames at gcc dot gnu.org --- Comment #3 from Sam James <sjames at gcc dot gnu.org> --- For 14/15, it seems gone with -O2, but I see it with -Og. ^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/108467] false positive -Wmaybe-uninitialized warning at -O1 or higher 2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net ` (2 preceding siblings ...) 2024-06-15 2:07 ` sjames at gcc dot gnu.org @ 2024-06-15 9:41 ` vincent-gcc at vinc17 dot net 3 siblings, 0 replies; 5+ messages in thread From: vincent-gcc at vinc17 dot net @ 2024-06-15 9:41 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108467 --- Comment #4 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- (In reply to Sam James from comment #3) > For 14/15, it seems gone with -O2, but I see it with -Og. The warning still occurs with -O1 too. ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-06-15 9:41 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2023-01-19 16:08 [Bug tree-optimization/108467] New: false positive -Wmaybe-uninitialized warning at -O1 or higher vincent-gcc at vinc17 dot net 2023-01-19 16:15 ` [Bug tree-optimization/108467] " pinskia at gcc dot gnu.org 2023-01-20 8:28 ` rguenth at gcc dot gnu.org 2024-06-15 2:07 ` sjames at gcc dot gnu.org 2024-06-15 9:41 ` vincent-gcc at vinc17 dot net
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