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Re: Ping : [PATCH] [gcc, combine] PR46164: Don't combine the insns if a volatile register is contained.


Terry Guo <flameroc@gmail.com> writes:
> On Thu, Feb 26, 2015 at 1:55 PM, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
>> On Tue, Feb 17, 2015 at 11:39:34AM +0800, Terry Guo wrote:
>>> On Sun, Feb 15, 2015 at 7:35 PM, Segher Boessenkool
>>> <segher@kernel.crashing.org> wrote:
>>> > Hi Terry,
>>> >
>>> > I still think this is stage1 material.
>>> >
>>> >> + /* Don't combine if dest contains a user specified register and
>>> >> i3 contains
>>> >> + ASM_OPERANDS, because the user specified register (same with
>>> >> dest) in i3
>>> >> +     would be replaced by the src of insn which might be different with
>>> >> +     the user's expectation.  */
>>> >
>>> > "Do not eliminate a register asm in an asm input" or similar?  Text
>>> > explaining why REG_USERVAR_P && HARD_REGISTER_P works here would be
>>> > good to have, too.
>>
>>> diff --git a/gcc/combine.c b/gcc/combine.c
>>> index f779117..aeb2854 100644
>>> --- a/gcc/combine.c
>>> +++ b/gcc/combine.c
>>> @@ -1779,7 +1779,7 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn *pred ATTRIBUTE_UNUSED,
>>>  {
>>>    int i;
>>>    const_rtx set = 0;
>>> -  rtx src, dest;
>>> +  rtx src, dest, asm_op;
>>>    rtx_insn *p;
>>>  #ifdef AUTO_INC_DEC
>>>    rtx link;
>>> @@ -1914,6 +1914,14 @@ can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn *pred ATTRIBUTE_UNUSED,
>>>    set = expand_field_assignment (set);
>>>    src = SET_SRC (set), dest = SET_DEST (set);
>>>
>>> +  /* Use REG_USERVAR_P and HARD_REGISTER_P to check whether DEST is a user
>>> +     specified register, and do not eliminate such register if it is in an
>>> +     asm input because we may end up with something different with user's
>>> +     expectation.  */
>>
>> That doesn't explain why this will hit (almost) only on register asms.
>> The user's expectation doesn't matter that much either: GCC would violate
>> its own documentation / promises, that matters more ;-)
>>
>>> +  if (REG_P (dest) && REG_USERVAR_P (dest) && HARD_REGISTER_P (dest)
>>> +      && ((asm_op = extract_asm_operands (PATTERN (i3))) != NULL))
>>
>> You do not need the temporary variable, nor the != 0 or the extra parens;
>> just write
>>
>>      && extract_asm_operands (PATTERN (i3))
>>
>> Cheers,
>>
>>
>> Segher
>
> Thanks for comments. Patch is updated now. Please review again.

Looks good to me FWIW.

Thanks,
Richard


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