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From: Richard Sandiford <richard.sandiford@arm.com>
To: Richard Biener <rguenther@suse.de>
Mail-Followup-To: Richard Biener <rguenther@suse.de>,"Kewen.Lin" <linkw@linux.ibm.com>,  "juzhe.zhong\@rivai.ai" <juzhe.zhong@rivai.ai>,  gcc-patches <gcc-patches@gcc.gnu.org>, richard.sandiford@arm.com
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Subject: Re: decremnt IV patch create fails on PowerPC
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Date: Tue, 30 May 2023 12:29:29 +0100
In-Reply-To: <nycvar.YFH.7.77.849.2305301039460.4723@jbgna.fhfr.qr> (Richard
	Biener's message of "Tue, 30 May 2023 10:43:34 +0000 (UTC)")
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Richard Biener <rguenther@suse.de> writes:
>> But how easy would it be to extend SCEV analysis, via a pattern match?
>> The evolution of the IV phi wrt the inner loop is still a normal SCEV.
>
> No, the IV isn't a normal SCEV, the final value is different.

Which part of the IV though?  Won't all executions of the latch edge
decrement the IV phi (and specifically the phi) by VF (and only VF)?
So if we analyse the IV phi wrt the inner loop, the IV phi is simply
{ initial, -, VF }.

I agree "IV phi - step" isn't a SCEV, but that doesn't seem fatal.

Richard