[Bug middle-end/88345] -Os overrides -falign-functions=N on the command line

["kito at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345

Kito Cheng <kito at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kito at gcc dot gnu.org

--- Comment #7 from Kito Cheng <kito at gcc dot gnu.org> ---
We are hitting this issue on RISC-V, and got some complain from linux kernel
developers, but in different form as the original report, we found cold
function or any function is marked as cold by `-fguess-branch-probability` are
all not honor to the -falign-functions=N setting, that become problem on some
linux kernel feature since they want to control the minimal alignment to make
sure they can atomically update the instruction which require align to 4 byte.

However current GCC behavior can't guarantee that even -falign-functions=4 is
given, there is 3 option in my mind:

1. Fix -falign-functions=N, let it work as expect on -Os and all cold functions
2. Force align to 4 byte if -fpatchable-function-entry is given, that's should
be doable by adjust RISC-V's FUNCTION_BOUNDARY
3. Adjust RISC-V's FUNCTION_BOUNDARY to let it honor to -falign-functions=N
4. Adding a -malign-functions=N...Okay, I know that suck idea, x86 already
deprecated that.

But I think ideally this should fixed by 1 option if possible.

Testcase from RISC-V kernel guy:
```
/* { dg-do compile } */
/* { dg-options "-march=rv64gc -mabi=lp64d -O1 -falign-functions=128" } */
/* { dg-final { scan-assembler-times ".align 7" 2 } } */

// Using 128 byte align rather than 4 byte align since it easier to observe.

__attribute__((__cold__)) void a() {} // This function isn't align to 128 byte
void b() {} // This function align to 128 byte.
```

Proposed fix:
```
diff --git a/gcc/varasm.c b/gcc/varasm.c
index 49d5cda122f..6f8ed85fea9 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -1907,8 +1907,7 @@ assemble_start_function (tree decl, const char *fnname)
      Note that we still need to align to DECL_ALIGN, as above,
      because ASM_OUTPUT_MAX_SKIP_ALIGN might not do any alignment at all.  */
   if (! DECL_USER_ALIGN (decl)
-      && align_functions.levels[0].log > align
-      && optimize_function_for_speed_p (cfun))
+      && align_functions.levels[0].log > align)
     {
 #ifdef ASM_OUTPUT_MAX_SKIP_ALIGN
       int align_log = align_functions.levels[0].log;

```