[Bug middle-end/45631] New: devirtualization with profile feedback does not work for function pointers

[andi-gcc at firstfloor dot org]

Following simple example:

#include <stdio.h>

static void a(void)
{
        printf("a\n");
}

static void b(void)
{
        printf("b\n");
}

static void __attribute__((noinline)) do_call(void (*p)(void))
{
        p();
}

int main(void)
{
        int i;
        for (i = 0; i < 30; i++)
                do_call((i%4) < 3 ? a : b);

        return 0;
}

I compile it with profile feedback and generate feedback data

% gcc -O3 -fprofile-generate x.c
% ./a.out
... output ...
% gcc -O3 -fprofile-use x.c

Examining the output do_call of the final code is just:

0000000000400520 <do_call>:
  400520:       ff e7                   jmpq   *%rdi


But I would have expected the profile feedback code to detect
that a is much more likely than b in the indirect call
and inline a through devirtualization.


-- 
           Summary: devirtualization with profile feedback does not work
                    for function pointers
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andi-gcc at firstfloor dot org
  GCC host triplet: x86_64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45631