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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/96564] [11 Regression] New maybe use of uninitialized variable warning since r11-959 Date: Tue, 11 Aug 2020 17:10:10 +0000 [thread overview] Message-ID: <bug-96564-4-dRlaTr71p0@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-96564-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96564 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- See Also| |https://gcc.gnu.org/bugzill | |a/show_bug.cgi?id=87313 Keywords| |alias, diagnostic, | |missed-optimization --- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> --- r11-959 enabled -Wuninitialized for allocated objects (alloca/VLA and malloc). The underlying problem is the failure to take advantage of the non-aliasing guarantee of the return value of these functions. One report that describes this limitation is pr87313. A slightly simpler but even more obvious test case is: $ cat pr96564.c && gcc -O2 -S -Wall -Wextra -fdump-tree-optimized=/dev/stdout pr96564.c void f (int *x) { int a[*x]; if (a != x) *a = 0; *x = *a; } pr96564.c: In function ‘f’: pr96564.c:8:6: warning: ‘*(<unknown>)[0]’ may be used uninitialized [-Wmaybe-uninitialized] 8 | *x = *a; | ~~~^~~~ ;; Function f (f, funcdef_no=0, decl_uid=1931, cgraph_uid=1, symbol_order=0) Removing basic block 5 f (int * x) { int[0:D.1936] * a.0; sizetype _2; int _8; sizetype _9; int prephitmp_18; int pretmp_20; <bb 2> [local count: 1073741824]: _8 = *x_1(D); _2 = (sizetype) _8; _9 = _2 * 4; a.0_11 = __builtin_alloca_with_align (_9, 32); if (x_1(D) != a.0_11) goto <bb 4>; [70.00%] else goto <bb 3>; [30.00%] <bb 3> [local count: 322122544]: pretmp_20 = (*a.0_11)[0]; <bb 4> [local count: 1073741824]: # prephitmp_18 = PHI <pretmp_20(3), 0(2)> *x_1(D) = prephitmp_18; return; }
next prev parent reply other threads:[~2020-08-11 17:10 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-08-11 7:30 [Bug middle-end/96564] New: New maybe use of uninitialized variable warning since GCC >10 stefansf at linux dot ibm.com 2020-08-11 9:27 ` [Bug middle-end/96564] " glisse at gcc dot gnu.org 2020-08-11 9:47 ` [Bug middle-end/96564] [11 Regression] New maybe use of uninitialized variable warning since r11-959 jakub at gcc dot gnu.org 2020-08-11 17:10 ` msebor at gcc dot gnu.org [this message] 2020-08-11 17:24 ` msebor at gcc dot gnu.org 2020-08-25 8:20 ` rguenth at gcc dot gnu.org 2021-01-14 9:19 ` rguenth at gcc dot gnu.org 2021-02-11 10:48 ` jakub at gcc dot gnu.org 2021-04-27 11:39 ` [Bug middle-end/96564] [11/12 " jakub at gcc dot gnu.org 2021-07-28 7:05 ` rguenth at gcc dot gnu.org 2022-04-21 7:48 ` rguenth at gcc dot gnu.org 2023-03-14 5:00 ` [Bug middle-end/96564] [11/12/13 " pinskia at gcc dot gnu.org 2023-05-29 10:03 ` [Bug middle-end/96564] [11/12/13/14 " jakub at gcc dot gnu.org 2024-03-10 22:49 ` law at gcc dot gnu.org 2024-03-11 10:23 ` rguenth at gcc dot gnu.org 2024-03-11 13:26 ` rguenth at gcc dot gnu.org 2024-03-11 15:20 ` amacleod at redhat dot com 2024-03-12 7:37 ` rguenth at gcc dot gnu.org 2024-05-16 11:23 ` [Bug middle-end/96564] [11/12/13/14/15 " rguenth at gcc dot gnu.org 2024-05-16 12:44 ` cvs-commit at gcc dot gnu.org 2024-05-16 14:27 ` aldyh at gcc dot gnu.org
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