On Thu, 2025-01-30 at 09:03 +0000, Jonathan Wakely via Gcc wrote: > On Thu, 30 Jan 2025, 09:00 Dmitry Antipov, <dmanti...@yandex.ru> > wrote: > > > With (probably) -Wmaybe-uninitialized and/or -Wextra, shouldn't the > > compiler emit > > warning about possibly uninitialized 'y' passed to 'ddd()' in the > > example > > below? > > > > Warnings are always going to be somewhat unreliable. You need a > proper > static analyser to detect all problems on all possible paths (- > fanalyzer > might do better here, I didn't check).
FWIW -fanalyzer doesn't warn: https://godbolt.org/z/EvcnMv767 unless I add -fno-analyzer-state-merge https://godbolt.org/z/dr1eTGj53 which gives: <source>: In function 'aaa': <source>:24:9: warning: use of uninitialized value 'y' [CWE-457] [-Wanalyzer-use-of-uninitialized-value] 24 | x += ddd (t, y); /* then 'y' is passed to ddd() uninitialized */ | ^~~~~~~~~~ 'aaa': events 1-7 13 | int x = 0, y; /* 'y' is uninitialized */ | ^ | | | (1) region created on stack here | (2) capacity: 4 bytes 14 | 15 | if (t->a) /* if this condition is true */ | ~ | | | (3) following 'true' branch... ─>─┐ | │ | │ |┌────────────────────────────────────────┘ 16 |│ goto l; |│ ~~~~ |│ | |└────>(4) ...to here ...... 21 | if (t->b) /* and this condition is false */ | ~ | | | (5) following 'false' branch... ─>─┐ | │ ...... | │ |┌─────────────────────────────────────────┘ 24 |│ x += ddd (t, y); /* then 'y' is passed to ddd() uninitialized */ |│ ~~~~~~~~~~ |│ | |└───────>(6) ...to here | (7) ⚠️ use of uninitialized value 'y' here Arguably the state-merging code could be smarter here; I haven't investigated the details, but have filed it as PR analyzer/118702 here: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118702 Thanks Dave > > > > > struct T { > > int a; > > int b; > > }; > > > > extern int bbb (struct T *, int *); > > extern int ccc (struct T *, int *); > > extern int ddd (struct T *, int); > > > > int > > aaa (struct T *t) > > { > > int x = 0, y; /* 'y' is uninitialized */ > > > > if (t->a) /* if this condition is true */ > > goto l; > > > > x += bbb (t, &y); > > > > l: > > if (t->b) /* and this condition is false */ > > x += ccc (t, &y); > > > > x += ddd (t, y); /* then 'y' is passed to ddd() > > uninitialized */ > > > > return x; > > } > > > > Dmitry > > > > >
