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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
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115423

--- 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")=3D=3D0 ||
strcmp(c, "ABCDEFGHfoobar")=3D=3D0.

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 pag=
e),
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.)=