On Thu, Dec 18, 2014 at 5:51 AM, Jakub Jelinek <ja...@redhat.com> wrote:
> On Thu, Dec 18, 2014 at 02:24:06PM +0100, Uros Bizjak wrote:
>> > It removed 14309 redundant "xor %eax,%eax" instructions and saved about
>> > 27KB. I am currently running the new kernel without any problem. OK
>> > for trunk?
>>
>> How about skipping RAX setup unconditionally for !TARGET_SSE? Please
>> see ix86_conditional_register_usage, where SSE registers are squashed
>> for !TARGET_SSE, so it is not possible to use them even in the inline
>> asm.
>
> I'd say a problem is if a -mno-sse TU calls a vararg function (obviously
> it can't pass any float/double arguments) to a function in a TU compiled
> with -msse2 or higher where the stdarg pass can't figure out anything, say
> #include <stdarg.h>
> extern void bar (int, va_list);
> void
> foo (int x, ...)
> {
> va_list ap;
> va_start (ap, x);
> bar (x, ap);
> va_end (ap);
> }
> If foo is compiled with gcc 4.4 and earlier, it might crash when called from
This was checked into GCC 4.4:
commit d5d9458afdae9056a9624ae9c332dbcdc2f383be
Author: jakub <jakub@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Tue Sep 2 19:49:41 2008 +0000
* config/i386/i386.c (X86_64_VARARGS_SIZE): Removed.
(setup_incoming_varargs_64): Assume cum != NULL. Set/check
ix86_varargs_gpr_size and ix86_varargs_fpr_size. Use
ix86_varargs_gpr_size instead of X86_64_REGPARM_MAX.
Don't set ix86_save_varrargs_registers.
(ix86_setup_incoming_varargs): Assume cum != NULL.
(ix86_va_start): Check ix86_varargs_gpr_size and
ix86_varargs_fpr_size instead of cfun->va_list_gpr_size and
cfun->va_list_fpr_size, respectively. Subtract 8*X86_64_REGPARM_MAX
from frame pointer if ix86_varargs_gpr_size == 0.
(ix86_compute_frame_layout): Updated.
* config/i386/i386.h (ix86_save_varrargs_registers): Removed.
(ix86_varargs_gpr_size): Define.
(ix86_varargs_fpr_size): Likewise.
(machine_function): Remove save_varrargs_registers.
Add varargs_gpr_size and varargs_fpr_size.
* gcc.target/i386/amd64-abi-3.c: New test.
* gcc.target/i386/amd64-abi-4.c: Likewise.
* gcc.target/i386/amd64-abi-5.c: Likewise.
* gcc.target/i386/amd64-abi-6.c: Likewise.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@139910
138bc75d-0d04-0410-961f-82ee72b054a4
> -mno-sse caller that would not xor %eax,%eax. If foo is compiled with gcc
> 4.5? and higher, then it might just randomly save all the xmm registers to
GCC 4.4 is fine.
> stack (as the test is %al != 0, I think it will be more likely that it will
> save it unnecessarily than not).
> So I view H.J.'s new option as a user guarantee the callee will be also
> -mno-sse.
>
If foo may be compiled by GCC 4.3 or older, we can't skip setting up
RAX in foo's
callers. Such an option is useful.
--
H.J.
