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From: Jeff Law <jeffreyalaw@gmail.com>
To: Richard Biener <rguenther@suse.de>, gcc-patches@gcc.gnu.org
Cc: Jan Hubicka <hubicka@ucw.cz>
Subject: Re: [PATCH] Improve DSE to handle stores before __builtin_unreachable ()
Date: Tue, 20 Jun 2023 07:27:41 -0600	[thread overview]
Message-ID: <7bddf09a-1535-8bcb-94da-8ad18b51963f@gmail.com> (raw)
In-Reply-To: <20230620070009.C11983858D1E@sourceware.org>



On 6/20/23 00:59, Richard Biener via Gcc-patches wrote:
> DSE isn't good at identifying program points that end lifetime
> of variables that are not associated with virtual operands.  But
> at least for those that end basic-blocks we can handle the simple
> case where this ending is in the same basic-block as the definition
> we want to elide.  That should catch quite some common cases already.
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> 
> As you can see from the testcase I had to adjust this possibly can
> lead to more severe issues when one forgets a return (the C++ frontend
> places builtin_unreachable () there).  I'm still planning to push
> this improvement unless I hear objections.
> 
> Thanks,
> Richard.
> 
> 	* tree-ssa-dse.cc (dse_classify_store): When we found
> 	no defs and the basic-block with the original definition
> 	ends in __builtin_unreachable[_trap] the store is dead.
> 
> 	* gcc.dg/tree-ssa/ssa-dse-47.c: New testcase.
> 	* c-c++-common/asan/pr106558.c: Avoid undefined behavior
> 	due to missing return.
I thought during the introduction of erroneous path isolation that we 
concluded stores, calls and such had observable side effects that must 
be preserved, even when we hit a block that leads to __builtin_unreachable.

Don't get me wrong, I'm all for removing the memory references if it's 
safe to do so.

Jeff

       reply	other threads:[~2023-06-20 13:27 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20230620070009.C11983858D1E@sourceware.org>
2023-06-20 13:27 ` Jeff Law [this message]
2023-06-21  6:41   ` Richard Biener
2023-06-21  9:55     ` Jan Hubicka
2023-06-21 14:04     ` Jeff Law
2023-06-22  6:31       ` Richard Biener
2023-06-22 13:36         ` Jeff Law
2023-06-22 13:42           ` Jan Hubicka
2023-06-24 14:24             ` Jeff Law
2023-06-25 16:33               ` Jan Hubicka
2023-06-26 17:21   ` Jan Hubicka
2023-06-26 22:37     ` Jeff Law
2023-06-20  6:59 Richard Biener

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