On Wed, Jul 25, 2012 at 4:07 PM, Selvaraj, Senthil_Kumar
<[email protected]> wrote:
> Declaring a function with __attribute__((optimize("O0")) turns off inlining
> for the translation unit (atleast) containing the function (see output at the
> end). Is this expected behavior?
Not really. The optimize attribute processing should only affect flags it
saves. -f[no-]inline is not meaningful per function and we have the noinline
attribute for more proper handling.
That said, I consider the optimize attribute code seriously broken and
unmaintained (but sometimes useful for debugging - and only that).
> I tracked this down to the fact that when processing the optimize attribute
> with O0, flag_no_inline is set to 1 and is not restored back. The
> early_inliner pass in ipa-inline.c (obviously) skips processing if
> flag_no_inline is set, and therefore inlining does not occur. I did see that
> handle_optimize_attribute in c-family/c-common.c saves and restores whatever
> options have corresponding fields in struct cl_optimization, but inlining is
> not one of them. That I guess is happening because inline is not described as
> an "Optimization" option in common.opt.
>
> Test output
> ----------------
> $ cat test.c
> static void callee() { static int a; a++; }
> void caller() { callee(); }
> $
> $ ~/Code/gcc/repo/native_install/bin/gcc -O1 -fdump-tree-all -S test.c
> $
> $ cat test.c.*.optimized
>
> ;; Function caller (caller, funcdef_no=1, decl_uid=1358, cgraph_uid=1)
>
> caller ()
> {
> int a.0;
> int a.1;
> static int a;
> static int a;
>
> <bb 2>:
> a.0_3 = a;
> a.1_4 = a.0_3 + 1;
> a = a.1_4;
> return;
>
> }
>
> $ cat test.c
> static void callee() { static int a; a++; }
> void caller() { callee(); }
> static void somefunc() __attribute__((optimize("O0")));
> $
> $ ~/Code/gcc/repo/native_install/bin/gcc -O1 -fdump-tree-all -S test.c
> $
> $ cat test.c.*.optimized
>
> ;; Function callee (callee, funcdef_no=0, decl_uid=1355, cgraph_uid=0)
> callee ()
> {
> static int a;
> int a.1;
> int a.0;
>
> <bb 2>:
> a.0_1 = a;
> a.1_2 = a.0_1 + 1;
> a = a.1_2;
> return;
>
> }
>
> ;; Function caller (caller, funcdef_no=1, decl_uid=1358, cgraph_uid=1)
> caller ()
> {
> <bb 2>:
> callee ();
> return;
>
> }
>
> Regards
> Senthil
