[Bug target/60906] New: target attribute causes other attributes to be ignored

[harald at gigawatt dot nl]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60906

            Bug ID: 60906
           Summary: target attribute causes other attributes to be ignored
           Product: gcc
           Version: 4.8.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: harald at gigawatt dot nl

When the target attribute is used to select a function based on CPU, other
attributes get ignored. This can lead to missed optimisations and/or wrong
code, depending on the specific attribute.

Missed optimisation:

void foo() __attribute__((target("default"), noreturn));
void foo() __attribute__((target("arch=corei7"), noreturn));

void bar() { foo(); foo(); }

The second call to foo, and the following return, could be optimised away (and
are if the target attribute is not used).

Wrong code:

#include <assert.h>

int __attribute__((target("default"), regparm(3))) f(int x) { return x; }
int __attribute__((target("arch=corei7"), regparm(3))) f(int x) { return x; }

int main() {
  assert(f(3) == 3);
}

The assertion fails (on x86-32). Tested with 4.8.2.