https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87209
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |alias, missed-optimization
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-09-04
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Since we allow calloc to be declared with 'malloc' attribute the warning would
need to be special-cased on 'malloc'. Currently the warning uses the alias
machinery and that sees malloc clobber ints if not -fno-math-errno. The
machinery doesn't check whether the ref is to the memory returned by malloc.
/* If the call in statement CALL may clobber the memory reference REF
return true, otherwise return false. */
bool
call_may_clobber_ref_p_1 (gcall *call, ao_ref *ref)
{
...
/* Allocating memory does not have any side-effects apart from
being the definition point for the pointer. */
case BUILT_IN_MALLOC:
case BUILT_IN_ALIGNED_ALLOC:
case BUILT_IN_CALLOC:
case BUILT_IN_STRDUP:
case BUILT_IN_STRNDUP:
/* Unix98 specifies that errno is set on allocation failure. */
if (flag_errno_math
&& targetm.ref_may_alias_errno (ref))
return true;
return false;
note that -fno-math-errno doesn't fix it which is because of
/* Do not warn if it can be initialized outside this function.
If we did not reach function entry then we found killing
clobbers on all paths to entry. */
if (fentry_reached
/* ??? We'd like to use ref_may_alias_global_p but that
excludes global readonly memory and thus we get bougs
warnings from p = cond ? "a" : "b" for example. */
&& (!VAR_P (base)
|| is_global_var (base)))
continue;
so we do not handle uninit reads from pointer refs in this case.
