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* [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og [not found] <bug-78394-4@http.gcc.gnu.org/bugzilla/> @ 2021-04-01 20:42 ` msebor at gcc dot gnu.org 2021-04-02 8:02 ` linux at carewolf dot com ` (2 subsequent siblings) 3 siblings, 0 replies; 4+ messages in thread From: msebor at gcc dot gnu.org @ 2021-04-01 20:42 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78394 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Last reconfirmed|2017-07-20 00:00:00 |2021-4-1 Known to fail| |10.2.0, 11.0, 6.3.0, 7.0.1, | |8.3.0, 9.3.0 CC| |msebor at gcc dot gnu.org --- Comment #16 from Martin Sebor <msebor at gcc dot gnu.org> --- Reconfirming with GCC 11. Both instances of the warning go back as far as support for -Og so it's not a regression. With my patched GCC the output for just the first function is: pr78394.C: In function ‘float foo()’: pr78394.C:19:17: warning: ‘vy’ may be used uninitialized in this function [-Wmaybe-uninitialized] 19 | return vx + vy; | ^~ pr78394.C:13:15: note: used when ‘(a <= i)’ 13 | float vx, vy; | ^~ pr78394.C:13:15: note: ‘vy’ was declared here pr78394.C:19:17: warning: ‘vx’ may be used uninitialized in this function [-Wmaybe-uninitialized] 19 | return vx + vy; | ^~ pr78394.C:13:11: note: used when ‘(a <= i)’ 13 | float vx, vy; | ^~ pr78394.C:13:11: note: ‘vx’ was declared here The dump the warning sees is below as as noted the root cause is that the IL satisfies the conditions under which it's designed to trigger. So the only ways to avoid it would seem to be to either a) extend the warning to figure out that the condition it uses cannot happen (basically implement some of the optimizations disabled at -Og) or b) turn off -Wmaybe-uninitialized at -Og (i.e,. remove it from -Wall). I'm not in favor of (a) but (b) makes sense to me. I'd like to try to improve it for GCC 12 so unless I fail at that I'm not for disabling it at other optimization levels. float foo () { int i; float vy; float vx; int a; float _6; float _8; <bb 2> [local count: 118111600]: # VUSE <.MEM_4(D)> a_5 = b; if (a_5 <= 3) goto <bb 3>; [50.00%] else goto <bb 8>; [50.00%] <bb 8> [local count: 59055800]: goto <bb 4>; [100.00%] <bb 3> [local count: 59055800]: <bb 4> [local count: 118111600]: # a_1 = PHI <a_5(8), 4(3)> goto <bb 6>; [100.00%] <bb 5> [local count: 955630225]: _8 = (float) i_2; i_7 = i_2 + 1; <bb 6> [local count: 1073741824]: # i_2 = PHI <1(4), i_7(5)> # .MEM_3 = PHI <.MEM_4(D)(4), .MEM_3(5)> # vx_9 = PHI <vx_11(D)(4), _8(5)> # vy_10 = PHI <vy_12(D)(4), _8(5)> if (a_1 > i_2) goto <bb 5>; [89.00%] else goto <bb 7>; [11.00%] <bb 7> [local count: 118111600]: _6 = vx_9 + vy_10; # VUSE <.MEM_3> return _6; } ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og [not found] <bug-78394-4@http.gcc.gnu.org/bugzilla/> 2021-04-01 20:42 ` [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og msebor at gcc dot gnu.org @ 2021-04-02 8:02 ` linux at carewolf dot com 2021-06-01 9:21 ` marxin at gcc dot gnu.org 2022-08-31 11:04 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 4+ messages in thread From: linux at carewolf dot com @ 2021-04-02 8:02 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78394 --- Comment #17 from Allan Jensen <linux at carewolf dot com> --- Yes, if you can figure out exactly what optimization passes it needs, then we could disable the warning when those passes are disabled. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og [not found] <bug-78394-4@http.gcc.gnu.org/bugzilla/> 2021-04-01 20:42 ` [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og msebor at gcc dot gnu.org 2021-04-02 8:02 ` linux at carewolf dot com @ 2021-06-01 9:21 ` marxin at gcc dot gnu.org 2022-08-31 11:04 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 4+ messages in thread From: marxin at gcc dot gnu.org @ 2021-06-01 9:21 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78394 Bug 78394 depends on bug 100845, which changed state. Bug 100845 Summary: [11/12 Regression] False positive for -Werror=maybe-uninitialized since r11-959-gb825a22890740f34 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100845 What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og [not found] <bug-78394-4@http.gcc.gnu.org/bugzilla/> ` (2 preceding siblings ...) 2021-06-01 9:21 ` marxin at gcc dot gnu.org @ 2022-08-31 11:04 ` rguenth at gcc dot gnu.org 3 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2022-08-31 11:04 UTC (permalink / raw) To: gcc-bugs https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78394 Bug 78394 depends on bug 65244, which changed state. Bug 65244 Summary: Bogus -Wmaybe-uninitialized warning with posix_memalign() and -Og https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65244 What |Removed |Added ---------------------------------------------------------------------------- Status|ASSIGNED |RESOLVED Resolution|--- |FIXED ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-08-31 11:04 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <bug-78394-4@http.gcc.gnu.org/bugzilla/> 2021-04-01 20:42 ` [Bug tree-optimization/78394] False positives of maybe-uninitialized with -Og msebor at gcc dot gnu.org 2021-04-02 8:02 ` linux at carewolf dot com 2021-06-01 9:21 ` marxin at gcc dot gnu.org 2022-08-31 11:04 ` rguenth at gcc dot gnu.org
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