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From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/103310] null comparison with a weak symbol eliminated Date: Thu, 18 Nov 2021 00:40:01 +0000 [thread overview] Message-ID: <bug-103310-4-oRSMDkCJvY@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-103310-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103310 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Component|middle-end |c --- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> --- The test case below shows that storing the address of the alias in a local pointer avoids the problem. The dumps show that the problem is in the front end which folds the test of the address of the weak symbol to true. $ cat pr103310.c && gcc -Wall -O2 -S -fdump-tree-original=/dev/stdout -fdump-tree-optimized=/dev/stdout pr103310.c extern void alias (void); void call_alias (void) { __builtin_printf ("in %s: alias = %p\n", __func__, alias); if (alias) alias (); } void call_ptr_alias (void) { void (*p)(void) = alias; __builtin_printf ("in %s: alias = %p\n", __func__, p); if (p) p (); } extern void alias (void) __attribute__((weak)); pr103310.c: In function ‘call_alias’: pr103310.c:7:7: warning: the address of ‘alias’ will always evaluate as ‘true’ [-Waddress] 7 | if (alias) | ^~~~~ ;; Function call_alias (null) ;; enabled by -tree-original { static const char __func__[11] = "call_alias"; static const char __func__[11] = "call_alias"; __builtin_printf ((const char *) "in %s: alias = %p\n", (const char *) &__func__, alias); if (1) { alias (); } } ;; Function call_ptr_alias (null) ;; enabled by -tree-original { void (*<T349>) (void) p = alias; static const char __func__[15] = "call_ptr_alias"; static const char __func__[15] = "call_ptr_alias"; void (*<T349>) (void) p = alias; __builtin_printf ((const char *) "in %s: alias = %p\n", (const char *) &__func__, p); if (p != 0B) { p (); } } ;; Function call_alias (call_alias, funcdef_no=0, decl_uid=1945, cgraph_uid=1, symbol_order=0) void call_alias () { static const char __func__[11] = "call_alias"; <bb 2> [local count: 1073741824]: __builtin_printf ("in %s: alias = %p\n", &__func__, alias); alias (); [tail call] return; } ;; Function call_ptr_alias (call_ptr_alias, funcdef_no=1, decl_uid=1949, cgraph_uid=2, symbol_order=1) Removing basic block 5 void call_ptr_alias () { static const char __func__[15] = "call_ptr_alias"; <bb 2> [local count: 1073741824]: __builtin_printf ("in %s: alias = %p\n", &__func__, alias); if (alias != 0B) goto <bb 3>; [53.47%] else goto <bb 4>; [46.53%] <bb 3> [local count: 574129753]: alias (); [tail call] <bb 4> [local count: 1073741824]: return; }
next prev parent reply other threads:[~2021-11-18 0:40 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-11-17 22:01 [Bug middle-end/103310] New: " msebor at gcc dot gnu.org 2021-11-18 0:40 ` msebor at gcc dot gnu.org [this message] 2021-11-18 15:58 ` [Bug c/103310] " jason at gcc dot gnu.org 2021-12-01 18:24 ` cvs-commit at gcc dot gnu.org
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