[Bug c++/57514] New: -fno-align-functions doesn't work on member functions

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57514

            Bug ID: 57514
           Summary: -fno-align-functions doesn't work on member functions
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com

[hjl@gnu-6 tmp]$ cat a.cc
class Foo
{
public:
  void yyy ();
};

void
Foo::yyy ()
{
}
[hjl@gnu-6 tmp]$ gcc -S a.cc -fno-align-functions -O3 
[hjl@gnu-6 tmp]$ cat a.s
    .file    "a.cc"
    .text
    .align 2
    .globl    _ZN3Foo3yyyEv
    .type    _ZN3Foo3yyyEv, @function
_ZN3Foo3yyyEv:
.LFB0:
    .cfi_startproc
    rep
    ret
    .cfi_endproc
.LFE0:
    .size    _ZN3Foo3yyyEv, .-_ZN3Foo3yyyEv
[hjl@gnu-6 tmp]$ gcc -S a.cc -O3 
[hjl@gnu-6 tmp]$ cat a.s
    .file    "a.cc"
    .text
    .align 2
    .p2align 4,,15
    .globl    _ZN3Foo3yyyEv
    .type    _ZN3Foo3yyyEv, @function
_ZN3Foo3yyyEv:
.LFB0:
    .cfi_startproc
    rep
    ret
    .cfi_endproc
.LFE0:
    .size    _ZN3Foo3yyyEv, .-_ZN3Foo3yyyEv

C++ front end has

  /* If pointers to member functions use the least significant bit to
     indicate whether a function is virtual, ensure a pointer
     to this function will have that bit clear.  */
  if (TARGET_PTRMEMFUNC_VBIT_LOCATION == ptrmemfunc_vbit_in_pfn
      && TREE_CODE (type) == METHOD_TYPE
      && DECL_ALIGN (decl) < 2 * BITS_PER_UNIT)
    DECL_ALIGN (decl) = 2 * BITS_PER_UNIT;

But the function alignment is controlled by -falign-functions and
backends.  All member functions may be aligned to 16 byte on x86.
How does C++ run-tim use the least significant bit to indicate
whether a member function is virtual?