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From: "blubban at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115423] Inlined strcmp optimizes poorly
Date: Tue, 11 Jun 2024 10:08:27 +0000	[thread overview]
Message-ID: <bug-115423-4-RK7saO9bQd@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-115423-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115423

--- Comment #3 from Alfred Agrell <blubban at gmail dot com> ---
strcmp (c, "ABCDEFGHabcdefgh") || strcmp (c, "ABCDEFGHfoobar") can safely be
optimized to 1, you're thinking of strcmp(c, "ABCDEFGHabcdefgh")==0 ||
strcmp(c, "ABCDEFGHfoobar")==0.

Optimizing to multi-byte reads would be a wrong-code. If strcmp(c, "1234567")
does an eight-byte read, it'll segfault if c is {'e',0} four bytes before an
unmapped page.

Even if limiting it to aligned reads (can't segfault without crossing a page),
it'll annoy Valgrind.

(Large reads would be safe if lhs is char[8] and not char*, or if strlen is
checked before doing those reads, but both of those feel unlikely to me.)

      parent reply	other threads:[~2024-06-11 10:08 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-06-11  0:08 [Bug tree-optimization/115423] New: " blubban at gmail dot com
2024-06-11  4:24 ` [Bug tree-optimization/115423] " pinskia at gcc dot gnu.org
2024-06-11  9:48 ` rguenth at gcc dot gnu.org
2024-06-11 10:08 ` blubban at gmail dot com [this message]

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