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From: Jeff Law <jeffreyalaw@gmail.com>
To: Manolis Tsamis <manolis.tsamis@vrull.eu>,
	gcc-patches@gcc.gnu.org,
	Philipp Tomsich <philipp.tomsich@vrull.eu>,
	Robin Dapp <rdapp@linux.ibm.com>,
	Jakub Jelinek <jakub@redhat.com>,
	richard.sandiford@arm.com
Subject: Re: [PATCH v3 2/4] ifcvt: Allow more operations in multiple set if conversion
Date: Fri, 10 Nov 2023 14:53:20 -0700	[thread overview]
Message-ID: <a8e6cf63-fddc-41bc-99ac-0cd2f28b2a40@gmail.com> (raw)
In-Reply-To: <mpt4jimpf87.fsf@arm.com>



On 10/19/23 13:46, Richard Sandiford wrote:
>> +      /* Allow a wide range of operations and let the costing function decide
>> +	 if the conversion is worth it later.  */
>> +      enum rtx_code code = GET_CODE (src);
>> +      if (!(CONSTANT_P (src)
>> +	    || code == REG
>> +	    || code == SUBREG
>> +	    || code == ZERO_EXTEND
>> +	    || code == SIGN_EXTEND
>> +	    || code == NOT
>> +	    || code == NEG
>> +	    || code == PLUS
>> +	    || code == MINUS
>> +	    || code == AND
>> +	    || code == IOR
>> +	    || code == MULT
>> +	    || code == ASHIFT
>> +	    || code == ASHIFTRT
>> +	    || code == NE
>> +	    || code == EQ
>> +	    || code == GE
>> +	    || code == GT
>> +	    || code == LE
>> +	    || code == LT
>> +	    || code == GEU
>> +	    || code == GTU
>> +	    || code == LEU
>> +	    || code == LTU
>> +	    || code == COMPARE))
>>   	return false;
> 
> I'm nervous about lists of operations like these, for two reasons:
> 
> (1) It isn't obvious what criteria are used to select the codes.
> 
> (2) It requires the top-level code to belong to a given set, but it
>      allows subrtxes of src to be arbitrarily complex.  E.g. (to pick
>      a silly example) a toplevel (popcount ...) would be rejected, but
>      (plus (popcount ...) (const_int 1)) would be OK.
> 
> Could we just remove this condition instead?
I'd be all for that.    We've actually got a similar problem in Joern's 
ext-dce code that I'm working on.  At least in that case I think we'll 
be able to enumerate how/why things are on the list if we still need it 
after the cleanup phase.

So I think the guidance on patch #2 would be to remove the list entirely 
if we can.

jeff

  reply	other threads:[~2023-11-10 21:53 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-30 10:13 [PATCH v3 0/4] ifcvt: Allow if conversion of arithmetic in basic blocks with multiple sets Manolis Tsamis
2023-08-30 10:13 ` [PATCH v3 1/4] ifcvt: handle sequences that clobber flags in noce_convert_multiple_sets Manolis Tsamis
2023-10-19 19:41   ` Richard Sandiford
2023-10-20  7:04     ` Robin Dapp
2023-10-20  9:16       ` Richard Sandiford
2023-11-10 21:48         ` Jeff Law
2023-11-10 21:31       ` Jeff Law
2023-11-10 21:25     ` Jeff Law
2024-04-23 10:58     ` Manolis Tsamis
2023-08-30 10:13 ` [PATCH v3 2/4] ifcvt: Allow more operations in multiple set if conversion Manolis Tsamis
2023-10-19 19:46   ` Richard Sandiford
2023-11-10 21:53     ` Jeff Law [this message]
2023-11-13 12:47     ` Manolis Tsamis
2024-04-23 11:00     ` Manolis Tsamis
2023-08-30 10:13 ` [PATCH v3 3/4] ifcvt: Handle multiple rewired regs and refactor noce_convert_multiple_sets Manolis Tsamis
2023-11-10 23:20   ` Jeff Law
2023-11-13 12:40     ` Manolis Tsamis
2023-11-21 18:10       ` Manolis Tsamis
2023-08-30 10:14 ` [PATCH v3 4/4] ifcvt: Remove obsolete code for subreg handling in noce_convert_multiple_sets Manolis Tsamis
2023-11-10 22:03   ` Jeff Law
2023-11-13 12:43     ` Manolis Tsamis
2023-11-21 18:08       ` Manolis Tsamis
2023-09-18  8:18 ` [PATCH v3 0/4] ifcvt: Allow if conversion of arithmetic in basic blocks with multiple sets Manolis Tsamis
2023-10-19  6:53   ` Manolis Tsamis

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