From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=Qrar=CL=kam.mff.cuni.cz=hubicka@sourceware.org>
Received: from nikam.ms.mff.cuni.cz (nikam.ms.mff.cuni.cz [195.113.20.16])
	by sourceware.org (Postfix) with ESMTPS id 1E16E3858CD1
	for <gcc-patches@gcc.gnu.org>; Fri, 23 Jun 2023 13:19:03 +0000 (GMT)
DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 1E16E3858CD1
Authentication-Results: sourceware.org; dmarc=fail (p=none dis=none) header.from=ucw.cz
Authentication-Results: sourceware.org; spf=none smtp.mailfrom=kam.mff.cuni.cz
Received: by nikam.ms.mff.cuni.cz (Postfix, from userid 16202)
	id 289AD28AEDC; Fri, 23 Jun 2023 15:19:01 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ucw.cz; s=gen1;
	t=1687526342;
	h=from:from:reply-to:subject:subject:date:date:message-id:message-id:
	 to:to:cc:cc:mime-version:mime-version:content-type:content-type:
	 in-reply-to:in-reply-to:references:references;
	bh=QuaEECRMzPVclH5zmdbynUMGiQH2VoH+cYsUSoKTzyo=;
	b=kecFgggdqtMS+n7PtXaYyErKBZm3HspqzbbxzjQlq8eewZwcfLU/QlufQ2q3x7Jy4bxPw8
	izZNoXTqCGXBFscErPauj58Qh8dZ4VeKKUCsR84D6Sg8UUclt7OZt5hqPfgGadgzmftQqu
	+90d7XVwpl3h+mur9LRey2ALei3AV7M=
Date: Fri, 23 Jun 2023 15:19:01 +0200
From: Jan Hubicka <hubicka@ucw.cz>
To: Richard Biener <richard.guenther@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: Do not account __builtin_unreachable guards in inliner
Message-ID: <ZJWbxZmhAk+AdaMi@kam.mff.cuni.cz>
References: <ZJAJMPiUB4oxqZBR@kam.mff.cuni.cz>
 <CAFiYyc2iZKEQC1ickKToXVratX-ZVF7dzQ=vvwcC9RvZbtq10w@mail.gmail.com>
 <ZJAqxK3h4ncImWcD@kam.mff.cuni.cz>
 <CAFiYyc3k0O5Ah0q=2j=81=JYcGQzwUa-BV=GOG5nGrFih=54=Q@mail.gmail.com>
 <ZJVvvKYDknwJAuYN@kam.mff.cuni.cz>
 <CAFiYyc1AAPvcXDKVUMDoTbc=0ByVJ9faq8uA+Ki08=fTUfUDig@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAFiYyc1AAPvcXDKVUMDoTbc=0ByVJ9faq8uA+Ki08=fTUfUDig@mail.gmail.com>
X-Spam-Status: No, score=-5.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org
List-Id: <gcc-patches.gcc.gnu.org>

> 
> So you need to feed it with extra info on the optimized out stmts because
> as-is it will not remove __builtin_unreachable ().  That means you're

My plan was to add entry point to tree-ssa-dce that will take an
set of stmts declared dead by external force and will do the usual mark
stage bypassing mark_stmt_if_necessary if the stmt is in the set of
deads.

> doing the find_obviously_necessary_stmts manually, skipping the
> conditional and all stmts it controls to the __builtin_unreachable () path?
> 
> I also think you want something cheaper than non-cd-dce mark, you also don't
> want to bother with stores/loads?

You are probably right. cd-dce marking became bit of a monster and I do
not want to care about memory.
One can add extra flag to avoid processing of memory, but the code I
would re-use is quite small.

I can do my own mark&sweep  just considering phis, pre-identified
conditionals and basic gimple_assigns with no side effects as possibly
unnecesary stmts.  I can completely ignore debug stmts.

So it should be one pass through the statments to populate the worklist
& simple walk of the ssa graph to propagae it.

> 
> Also when you only do this conditional how do you plan to use the result?

Well, the analysis is a loop that walks all basic blocks and then all
stmts.  I can keep track if computation of live stmts was done and in
that case query the flag assume it is true otherwise.

Honza