Re: [PATCH] PR target/66819: Allow indirect sibcall with register arguments

[Uros Bizjak <ubizjak at gmail dot com>]

On Fri, Jul 10, 2015 at 7:10 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Jul 10, 2015 at 9:30 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
>> On Thu, Jul 9, 2015 at 12:54 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> Indirect sibcall with register arguments is OK when there is register
>>> available for argument passing.
>>>
>>> OK for trunk if there is no regression?
>>>
>>>
>>> H.J.
>>> ---
>>> gcc/
>>>
>>>         PR target/66819
>>>         * config/i386/i386.c (ix86_function_ok_for_sibcall): Allow
>>>         indirect sibcall with register arguments if register available
>>>         for argument passing.
>>>         (init_cumulative_args): Set cfun->machine->arg_reg_available_p
>>>         to cum->nregs != 0.

Please update the above entry for nregs > 0.

>>>         (function_arg_advance_32): Set cfun->machine->arg_reg_available_p
>>>         to 0 when setting cum->nregs = 0.
>>
>> Do we also need similar functionality for 64bit ABIs? What happens if
>> we are out of argument regs there?
>
> 64-bit is OK since we have rax, r10 and r11 as scratch registers which
> aren't used to pass arguments.

Maybe this fact should be added as a comment in some appropriate place.

>>>         * config/i386/i386.h (machine_function): Add arg_reg_available_p.
>>>
>>> gcc/testsuite/
>>>
>>>         PR target/66819
>>>         * gcc.target/i386/pr66819-1.c: New test.
>>>         * gcc.target/i386/pr66819-2.c: Likewise.
>>>         * gcc.target/i386/pr66819-3.c: Likewise.
>>>         * gcc.target/i386/pr66819-4.c: Likewise.
>>>         * gcc.target/i386/pr66819-5.c: Likewise.
>>> ---
>>>  gcc/config/i386/i386.c                    | 15 +++++++++------
>>>  gcc/config/i386/i386.h                    |  3 +++
>>>  gcc/testsuite/gcc.target/i386/pr66819-1.c |  8 ++++++++
>>>  gcc/testsuite/gcc.target/i386/pr66819-2.c |  8 ++++++++
>>>  gcc/testsuite/gcc.target/i386/pr66819-3.c | 10 ++++++++++
>>>  gcc/testsuite/gcc.target/i386/pr66819-4.c | 12 ++++++++++++
>>>  gcc/testsuite/gcc.target/i386/pr66819-5.c | 10 ++++++++++
>>>  7 files changed, 60 insertions(+), 6 deletions(-)
>>>  create mode 100644 gcc/testsuite/gcc.target/i386/pr66819-1.c
>>>  create mode 100644 gcc/testsuite/gcc.target/i386/pr66819-2.c
>>>  create mode 100644 gcc/testsuite/gcc.target/i386/pr66819-3.c
>>>  create mode 100644 gcc/testsuite/gcc.target/i386/pr66819-4.c
>>>  create mode 100644 gcc/testsuite/gcc.target/i386/pr66819-5.c
>>>
>>> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
>>> index 54ee6f3..85e59a8 100644
>>> --- a/gcc/config/i386/i386.c
>>> +++ b/gcc/config/i386/i386.c
>>> @@ -5628,12 +5628,12 @@ ix86_function_ok_for_sibcall (tree decl, tree exp)
>>>        if (!decl
>>>           || (TARGET_DLLIMPORT_DECL_ATTRIBUTES && DECL_DLLIMPORT_P (decl)))
>>>         {
>>> -         if (ix86_function_regparm (type, NULL) >= 3)
>>> -           {
>>> -             /* ??? Need to count the actual number of registers to be used,
>>> -                not the possible number of registers.  Fix later.  */
>>> -             return false;
>>> -           }
>>> +         /* FIXME: The symbol indirect call doesn't need a
>>> +            call-clobbered register.  But we don't know if
>>> +            this is a symbol indirect call or not  here.  */
>>> +         if (ix86_function_regparm (type, NULL) >= 3
>>> +             && !cfun->machine->arg_reg_available_p)
>>
>> Isn't enough to look at arg_reg_available here?
>
> We need to check ix86_function_regparm since nregs is 0 if
> -mregparm=N isn't used and pr65753.c will fail.

OK. Please add this comment, is not that obvious.

>
>>> +           return false;
>>>         }
>>>      }
>>>
>>> @@ -6567,6 +6567,7 @@ init_cumulative_args (CUMULATIVE_ARGS *cum,  /* Argument info to initialize */
>>>                     ? X86_64_REGPARM_MAX
>>>                     : X86_64_MS_REGPARM_MAX);
>>>      }
>>> +  cfun->machine->arg_reg_available_p = cum->nregs != 0;
>>
>> false instead of 0. This is a boolean.
>
> Updated.
>
>>>    if (TARGET_SSE)
>>>      {
>>>        cum->sse_nregs = SSE_REGPARM_MAX;
>>> @@ -6636,6 +6637,7 @@ init_cumulative_args (CUMULATIVE_ARGS *cum,  /* Argument info to initialize */
>>>           else
>>>             cum->nregs = ix86_function_regparm (fntype, fndecl);
>>>         }
>>> +      cfun->machine->arg_reg_available_p = cum->nregs != 0;
>>
>> IMO, cum->nregs > 0 would be more descriptive.
>
> Updated.
>
>>>        /* Set up the number of SSE registers used for passing SFmode
>>>          and DFmode arguments.  Warn for mismatching ABI.  */
>>> @@ -7584,6 +7586,7 @@ pass_in_reg:
>>>         {
>>>           cum->nregs = 0;
>>>           cum->regno = 0;
>>> +         cfun->machine->arg_reg_available_p = 0;
>>>         }
>>>        break;
>>>
>>> diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
>>> index 74334ff..0b6e304 100644
>>> --- a/gcc/config/i386/i386.h
>>> +++ b/gcc/config/i386/i386.h
>>> @@ -2479,6 +2479,9 @@ struct GTY(()) machine_function {
>>>    /* If true, it is safe to not save/restore DRAP register.  */
>>>    BOOL_BITFIELD no_drap_save_restore : 1;
>>>
>>> +  /* If true, there is register available for argument passing.  */
>>> +  BOOL_BITFIELD arg_reg_available_p : 1;
>>
>> This is not a predicate, but a boolean flag. Please remove _p from the name.
>
> Updated.
>
> Here is the updated patch.  OK for trunk?

OK with a small comment additions.

+  /* If true, there is register available for argument passing.  */
+  BOOL_BITFIELD arg_reg_available : 1;
+

Please mention here that this is for 32bit targets only.

Thanks,
Uros.