Re: Combine patch ping

[Richard Biener <rguenther@suse.de>]

> Am 11.04.2024 um 16:03 schrieb Segher Boessenkool <segher@kernel.crashing.org>:
> 
> On Wed, Apr 10, 2024 at 08:32:39PM +0200, Uros Bizjak wrote:
>>> On Wed, Apr 10, 2024 at 7:56 PM Segher Boessenkool
>>> <segher@kernel.crashing.org> wrote:
>>> This is never okay.  You cannot commit a patch without approval, *ever*.
> 
> This is the biggest issue, to start with.  It is fundamental.

I have approved the patch as you might have noticed.

Richard 

>>> That patch is also obvious -- obviously *wrong*, that is.  There are
>>> big assumptions everywhere in the compiler how a CC reg can be used.
>>> This violates that, as explained elsewhere.
>> 
>> Can you please elaborate what is wrong with this concrete patch.
> 
> The explanation of the patch is contradictory to how RTL works at all,
> so it is just wrong.  It might even do something sane, but I didn't get
> that far at all!
> 
> Write good email explanations, and a good proposed commit message.
> Please.  It is the only one people can judge a patch.  Well, apart
> from doing everything myself from first principles, ignoring everything
> you said, just looking at the patch itself, but that is a hundred times
> more work.  I don't do that.
> 
>> The
>> part that the patch touches has several wrong assumptions, and the
>> fixed "???" comment just emphasizes that. I don't see what is wrong
>> with:
>> 
>> (define_insn "@pushfl<mode>2"
>>  [(set (match_operand:W 0 "push_operand" "=<")
>>    (unspec:W [(match_operand 1 "flags_reg_operand")]
>>          UNSPEC_PUSHFL))]
>>  "GET_MODE_CLASS (GET_MODE (operands[1])) == MODE_CC"
>>  "pushf{<imodesuffix>}"
>>  [(set_attr "type" "push")
>>   (set_attr "mode" "<MODE>")])
> 
> What does it even mean?  What is a flags:CC?  You always always always
> need to say what is *in* the flags, if you want to use it as input
> (which is what unspec does).  CC is weird like this.  Most targets do
> not have distinct physical flags for every condition, only a few
> conditions are "alive" at any point in the program!
> 
>> it is just a push of the flags reg to the stack. If the push can't be
>> described in this way, then it is the middle end at fault, we can't
>> just change modes at will.
> 
> But that is not what this describes: it operates on the flags register
> in some unspecified way, and pushes the result of *that* to the stack.
> 
> (Stack pointer modification is not described here btw, should it be?  Is
> that magically implemented by the backend some way, via type=push
> perhaps?)
> 
> 
> Segher