[Bug c++/84294] New: missing warning for ignored attribute on a function template declaration

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84294

            Bug ID: 84294
           Summary: missing warning for ignored attribute on a function
                    template declaration
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

With bug 81544 resolved, GCC 8 warns on distinct declarations of the same
function with mutually exclusive attributes (such as const and pure).  In the
test case below this warning detects the conflict between the two declarations
of function f (and the uses of the function in ff() show that GCC does ignore
the pure attribute on the second declaration).

However, when the same pair of mutually exclusive attributes is specified on
declarations a function template GCC issues no such warning, even though it
also ignores the conflicting attribute as in the non-template case as the dump
shows.

$ cat u.C && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout u.C
[[gnu::const]] int f ();
[[gnu::pure]] int f ();   // Wattributes, pure ignored (good)

void ff (int *p)
{
  int i0 = f ();
  *p = 123;
  int i1 = f (); 
  if (i0 != i1)    // folded to false (good)
    __builtin_abort ();
}

template <class T> [[gnu::const]] T g ();
template <class T> [[gnu::pure]] T g ();   // pure ignored, warning missing

void gg (int *p)
{
  int i0 = g<int>();
  *p = 123;
  int i1 = g<int>(); 
  if (i0 != i1)   // folded to false
    __builtin_abort ();
}
u.C:2:22: warning: ignoring attribute ‘pure’ because it conflicts with
attribute ‘const’ [-Wattributes]
 [[gnu::pure]] int f ();   // Wattributes, pure ignored (good)
                      ^
u.C:1:20: note: previous declaration here
 [[gnu::const]] int f ();
                    ^

;; Function ff (_Z2ffPi, funcdef_no=0, decl_uid=2355, cgraph_uid=0,
symbol_order=0)

ff (int * p)
{
  <bb 2> [local count: 1073741825]:
  *p_2(D) = 123;
  return;

}



;; Function gg (_Z2ggPi, funcdef_no=3, decl_uid=2366, cgraph_uid=1,
symbol_order=1)

gg (int * p)
{
  <bb 2> [local count: 1073741825]:
  *p_2(D) = 123;
  return;

}