https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83339
Bug ID: 83339
Summary: missing warning on a invalid attribute specified for a
builtin
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The patch for pr81544 enhanced GCC to detect declarations of functions with
conflicting attributes such as const and pure. However, the enhancement fails
to detect attributes on explicit declarations of standard library functions
that conflict with GCC's internal declarations of the same functions that do
not specify an attribute that's mutually exclusive with the explicit
declaration.
For instance, declaring the function puts() with either the const or pure
attribute makes no sense because puts() has side-effects. Yet GCC silently
accepts such declarations and makes use of the incorrect attribute to emit bad
code. For instance, GCC eliminates the calls to the function in the following
program:
$ gcc -O -S -Wall -fdump-tree-optimized=/dev/stdout d.c
int __attribute__ ((const)) puts (const char*);
int main ()
{
(void)puts ("foo"); // eliminated
(void)puts ("bar"); // eliminated
}
;; Function main (main, funcdef_no=0, decl_uid=1893, cgraph_uid=0,
symbol_order=0) (executed once)
main ()
{
<bb 2> [local count: 1073741825]:
return 0;
}
Besides detecting conflicts between two attributes, at least for built-in
functions, GCC should also detect conflicts between an explicit declaration
with an attribute and an implicit declaration without one.
