Add support for __builtin_frame_address(level)
authorKirill Smelkov <kirr@navytux.spb.ru>
Wed, 14 Nov 2012 23:31:49 +0000 (03:31 +0400)
committerKirill Smelkov <kirr@navytux.spb.ru>
Fri, 16 Nov 2012 06:22:14 +0000 (10:22 +0400)
commitb2a02961b4407ca76db5a66ca5ae855cbfba4e8e
tree3c0d00665fab9e4b352fcf5b1ad32063d955afb7
parente79c3533ecefd004daad8a27333582b2dad7f0b0
Add support for __builtin_frame_address(level)

Continuing d6072d37 (Add __builtin_frame_address(0)) implement
__builtin_frame_address for levels greater than zero, in order for
tinycc to be able to compile its own lib/bcheck.c after
cffb7af9 (lib/bcheck: Prevent __bound_local_new / __bound_local_delete
from being miscompiled).

I'm new to the internals, and used the most simple way to do it.
Generated code is not very good for levels >= 2, compare

                gcc                         tcc

    level=0     mov    %ebp,%eax            lea    0x0(%ebp),%eax

    level=1     mov    0x0(%ebp),%eax       mov    0x0(%ebp),%eax

    level=2     mov    0x0(%ebp),%eax       mov    0x0(%ebp),%eax
                mov    (%eax),%eax          mov    %eax,-0x10(%ebp)
                                            mov    -0x10(%ebp),%eax
                                            mov    (%eax),%eax

    level=3     mov    0x0(%ebp),%eax       mov    0x0(%ebp),%eax
                mov    (%eax),%eax          mov    (%eax),%ecx
                mov    (%eax),%eax          mov    (%ecx),%eax

But this is still an improvement and for bcheck we need level=1 for
which the code is good.

For the tests I had to force gcc use -O0 to not inline the functions.
And -fno-omit-frame-pointer just in case.

If someone knows how to improve the generated code - help is
appreciated.

Thanks,
Kirill

Cc: Michael Matz <matz@suse.de>
Cc: Shinichiro Hamaji <shinichiro.hamaji@gmail.com>
tccgen.c
tests/Makefile
tests/tcctest.c