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From: "scovich at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/37722] destructors not called on computed goto Date: Sat, 09 May 2009 08:17:00 -0000 [thread overview] Message-ID: <20090509081646.7481.qmail@sourceware.org> (raw) In-Reply-To: <bug-37722-2032@http.gcc.gnu.org/bugzilla/> ------- Comment #2 from scovich at gmail dot com 2009-05-09 08:16 ------- Computed gotos can easily make it impossible for the compiler to call constructors and destructors consistently. This is a major gotcha of computed gotos for people who have used normal gotos in C++ and expect destructors to be handled properly. Consider this program, for instance: #include <stdio.h> template<int i> struct foo { foo() { printf("%s<%d>\n", __FUNCTION__, i); } ~foo() { printf("%s<%d>\n", __FUNCTION__, i); } }; enum {RETRY, INSIDE, OUTSIDE, EVIL}; int bar(int idx) { static void* const gotos[] = {&&RETRY, &&INSIDE, &&OUTSIDE, &&EVIL}; bool first = true; { RETRY: foo<1> f1; if(first) { first = false; goto *gotos[idx]; } INSIDE: return 1; } if(0) { foo<2> f2; EVIL: return 2; } OUTSIDE: return 0; } int main() { for(int i=RETRY; i <= EVIL; i++) printf("%d\n", bar(i)); return 0; } Not only does it let you jump out of a block without calling destructors, it lets you jump into one without calling constructors: $ g++-4.4.0 -Wall -O3 scratch.cpp && ./a.out foo<1> foo<1> ~foo<1> 1 foo<1> ~foo<1> 1 foo<1> 0 foo<1> ~foo<2> 2 Ideally, the compiler could analyze possible destinations of the goto (best-effort, of course) and emit suitable diagnostics: scratch.cpp:16: warning: computed goto bypasses destructor of 'foo<1> f1' scratch.cpp:13: warning: declared here scratch.cpp:23: warning: possible jump to label 'EVIL' scratch.cpp:16: warning: from here scratch.cpp:22: warning: crosses initialization of 'foo<2> f2' In this particular example the compiler should be able to figure out that no labels reach a live f1 and call its destructor properly. If it's not feasible to analyze the possible destinations of the computed goto, regular control flow analysis should at least be able to identify potentially dangerous labels and gotos, e.g.: scratch.cpp:16: warning: computed goto may bypass destructor of 'foo<1> f1' scratch.cpp:13: warning: declared here scratch.cpp:23: warning: jump to label 'EVIL' scratch.cpp:8: warning: using a computed goto scratch.cpp:22: warning: may cross initialization of 'foo<2> f2' -- scovich at gmail dot com changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |scovich at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37722
next prev parent reply other threads:[~2009-05-09 8:17 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-10-02 20:46 [Bug c++/37722] New: " cburger at sunysb dot edu 2008-10-02 21:23 ` [Bug middle-end/37722] " pinskia at gcc dot gnu dot org 2009-05-09 8:17 ` scovich at gmail dot com [this message] [not found] <bug-37722-4@http.gcc.gnu.org/bugzilla/> 2013-01-11 14:52 ` timo.kreuzer at reactos dot org 2022-01-03 12:00 ` pinskia at gcc dot gnu.org 2022-01-03 17:33 ` jakub at gcc dot gnu.org 2023-07-19 16:46 ` ndesaulniers at google dot com 2023-12-21 2:07 ` cvs-commit at gcc dot gnu.org 2023-12-21 2:08 ` jason at gcc dot gnu.org 2024-01-03 4:23 ` egallager at gcc dot gnu.org
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