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>

1 files changed, 9 insertions, 6 deletions

diff --git a/tccgen.c b/tccgen.c
index f183913..f79da36 100644
--- a/tccgen.c
+++ b/tccgen.c
@@ -3665,20 +3665,23 @@ ST_FUNC void unary(void)
         break;
     case TOK_builtin_frame_address:
         {
+            int level;
             CType type;
             next();
             skip('(');
-            if (tok != TOK_CINT) {
-                tcc_error("__builtin_frame_address only takes integers");
-            }
-            if (tokc.i != 0) {
-                tcc_error("TCC only supports __builtin_frame_address(0)");
+            if (tok != TOK_CINT || tokc.i < 0) {
+                tcc_error("__builtin_frame_address only takes positive integers");
             }
+            level = tokc.i;
             next();
             skip(')');
             type.t = VT_VOID;
             mk_pointer(&type);
-            vset(&type, VT_LOCAL, 0);
+            vset(&type, VT_LOCAL, 0);       /* local frame */
+            while (level--) {
+                mk_pointer(&vtop->type);
+                indir();                    /* -> parent frame */
+            }
         }
         break;
 #ifdef TCC_TARGET_X86_64