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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/109609] [12/13/14 Regression] tail call for function even when passing a ptr which references a local array still Date: Tue, 25 Apr 2023 07:15:05 +0000 [thread overview] Message-ID: <bug-109609-4-dA0dWf03rc@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-109609-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109609 --- Comment #11 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #10) > On the first testcase reverting the offending rev. shows that it causes > > <bb 2> [local count: 137085152]: > - MEM[(char *)&buf + 12B] = 0; > - _19 = *id_8(D); > - if (_19 != 0) > + _18 = *id_7(D); > + if (_18 != 0) > > thus we DSE the store to the end. > > The issue is that the fnspec we have for strncpy says the access size > is specified by argument 3 but what it specified there is the _maximum_ > size read, not the actual size. So instead of "1cO313" it should be > "1cO31 " ('1' is somewhat odd then, it says we copy 'src' to 'dst' > but we only say the 'dst' write covers arg 3 size - I guess that's OK > for points-to analysis, the additional zeros written do not have pointers, > but if we use it differently it might be a wrong spec?) > > I'm scanning other builtins for similar issues. Note a different fix would be to re-interpret the case of reads and say the size is _up to_ the specified length, thus use ao_ref_init_from_ptr_and_range instead of _and_size. strncat, stpncpy, strncmp, strnlen, strndup are affected similarly. for functions like memchr I'm not sure if we can assume all 'n' bytes are read (thus if that would cause known overread -> undefined behavior). Honza? Any opinion? Fix for the testcase, but incomplete as noted above: diff --git a/gcc/builtins.cc b/gcc/builtins.cc index 0e06fa5b2e0..133707c1617 100644 --- a/gcc/builtins.cc +++ b/gcc/builtins.cc @@ -11562,11 +11562,12 @@ builtin_fnspec (tree callee) case BUILT_IN_STPCPY_CHK: return ".cO 1 "; case BUILT_IN_STRNCPY: + case BUILT_IN_STRNCPY_CHK: + return "1cO31 "; case BUILT_IN_MEMCPY: case BUILT_IN_MEMMOVE: case BUILT_IN_TM_MEMCPY: case BUILT_IN_TM_MEMMOVE: - case BUILT_IN_STRNCPY_CHK: case BUILT_IN_MEMCPY_CHK: case BUILT_IN_MEMMOVE_CHK: return "1cO313";
next prev parent reply other threads:[~2023-04-25 7:15 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-04-24 19:34 [Bug c++/109609] New: Invalid strncpy/strncat optimization in GCC 12 gburca-gnu at ebixio dot com 2023-04-24 19:38 ` [Bug middle-end/109609] " pinskia at gcc dot gnu.org 2023-04-24 19:40 ` pinskia at gcc dot gnu.org 2023-04-24 19:47 ` [Bug middle-end/109609] [12/13/14 Regression] " jakub at gcc dot gnu.org 2023-04-24 19:50 ` pinskia at gcc dot gnu.org 2023-04-24 19:52 ` [Bug middle-end/109609] [12/13/14 Regression] tail call for function even when passing a ptr which references a local array still jakub at gcc dot gnu.org 2023-04-24 19:56 ` pinskia at gcc dot gnu.org 2023-04-24 20:30 ` gburca-gnu at ebixio dot com 2023-04-24 20:52 ` jakub at gcc dot gnu.org 2023-04-25 6:30 ` rguenth at gcc dot gnu.org 2023-04-25 7:06 ` rguenth at gcc dot gnu.org 2023-04-25 7:15 ` rguenth at gcc dot gnu.org [this message] 2023-04-25 7:37 ` jakub at gcc dot gnu.org 2023-04-25 7:42 ` jakub at gcc dot gnu.org 2023-04-25 12:54 ` rguenth at gcc dot gnu.org 2023-04-25 14:53 ` cvs-commit at gcc dot gnu.org 2023-04-25 14:53 ` [Bug middle-end/109609] [12/13 " rguenth at gcc dot gnu.org 2023-04-25 16:14 ` gburca-gnu at ebixio dot com 2023-04-26 9:34 ` cvs-commit at gcc dot gnu.org 2023-04-26 10:41 ` cvs-commit at gcc dot gnu.org 2023-04-26 10:43 ` rguenth at gcc dot gnu.org
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