[Bug c/41483] New: gcc fails to elide indirect function call through immutable static variable

[avi at argo dot co dot il]

In the following code:

void h(void);

static void g()
{
    h();
}

static void (*f)(void) = g;

void k(void)
{
    f();
}

It is trivial to see that 'f' cannot change and thus the statement 'f();' can
be compiled as a direct call or jump.  gcc however emits an indirect jump on
x86_64:

   0:   48 8b 05 00 00 00 00    mov    0x0(%rip),%rax        # 7 <k+0x7>
                        3: R_X86_64_PC32        .rodata-0x4
   7:   ff e0                   jmpq   *%rax

Changing the initialization to 'f = h' produces the desired results:

0000000000000000 <k>:
   0:   e9 00 00 00 00          jmpq   5 <k+0x5>
                        1: R_X86_64_PC32        h-0x4

Both compiled with -O3 (though expected to work with -O2)


-- 
           Summary: gcc fails to elide indirect function call through
                    immutable static variable
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: avi at argo dot co dot il
 GCC build triplet: x86_64-pc-linux
  GCC host triplet: x86_64-pc-linux
GCC target triplet: x86_64-pc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41483