-fuse-caller-save - Enable for MIPS

[Tom de Vries]

On 28-04-14 12:26, Richard Sandiford wrote:
> Tom de Vries <Tom_deVries@mentor.com> writes:
>> On 27-04-14 12:27, Richard Sandiford wrote:
>>> Tom de Vries <Tom_deVries@mentor.com> writes:
>>>>    mips_emit_call_insn (rtx pattern, rtx orig_addr, rtx addr, bool lazy_p)
>>>>    {
>>>>      rtx insn, reg;
>>>>
>>>> -  insn = emit_call_insn (pattern);
>>>> +  emit_call_insn (pattern);
>>>> +  insn = last_call_insn ();
>>>>
>>>>      if (TARGET_MIPS16 && mips_use_pic_fn_addr_reg_p (orig_addr))
>>>>        {
>>>
>>> This change isn't necessary; emit_call_insn is defined to return a CALL_INSN.
>>>
>>
>> I dropped this change, as well as the change in the untyped_call expand, I
>> realized it's unnecessary.
>
> Why was the untyped_call part unnecessary?
>

The define_expand "untyped_call" uses GEN_CALL, which uses define_expand "call", 
which uses mips_expand_call, which uses mips_emit_call_insn, which adds the 
required clobbers.

>>> I'm a bit surprised that it doesn't work at -O1 for a simple test
>>> like this though.  What goes wrong?
>>>
>>
>> AFAIU now the problem is that the optimization doesn't trigger for -O0
>> and -01, because the register allocator behaves more conservatively.
>
> Hmm, is that just because -fcaller-saves is -O2 and above?
>  If so,
> should -fuse-caller-save imply -fcaller-saves?
>
> Thanks,
> Richard
>