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From: "mikpe at it dot uu dot se" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/40668] 64-bit sparc miscompiles memcpy of argument inside switch
Date: Tue, 07 Jul 2009 11:36:00 -0000 [thread overview]
Message-ID: <20090707113552.32226.qmail@sourceware.org> (raw)
In-Reply-To: <bug-40668-16771@http.gcc.gnu.org/bugzilla/>
------- Comment #3 from mikpe at it dot uu dot se 2009-07-07 11:35 -------
Confirmed, with gcc-4.3-20090705 it works, with gcc-4.4-20090630 it fails.
Compiling with -S and comparing the .s files it looks like 4.4 completely
mis-schedules the code for put_uint32:
put_uint32:
.register %g2, #scratch
.register %g3, #scratch
ldub [%sp+2175], %g1
ldub [%sp+2176], %g3
ldub [%sp+2177], %g2
ldub [%sp+2178], %g4
st %o0, [%sp+2175]
stb %g4, [%o1+3]
stb %g1, [%o1]
stb %g3, [%o1+1]
jmp %o7+8
stb %g2, [%o1+2]
Notice how the store of %o0 to the four bytes at %sp+2175 comes after the
corresponding byte loads, so %g1 to %g4 are loaded with garbage, likely zeroes.
In contrast, gcc-4.3 generates the store before the loads:
put_uint32:
.register %g2, #scratch
.register %g3, #scratch
st %o0, [%sp+2175]
ldub [%sp+2176], %g3
ldub [%sp+2177], %g4
ldub [%sp+2178], %g2
ldub [%sp+2175], %g1
stb %g2, [%o1+3]
stb %g1, [%o1]
stb %g3, [%o1+1]
jmp %o7+8
stb %g4, [%o1+2]
--
mikpe at it dot uu dot se changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mikpe at it dot uu dot se
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40668
next prev parent reply other threads:[~2009-07-07 11:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-07 5:56 [Bug target/40668] New: " blp at cs dot stanford dot edu
2009-07-07 5:58 ` [Bug target/40668] " blp at cs dot stanford dot edu
2009-07-07 5:58 ` blp at cs dot stanford dot edu
2009-07-07 11:36 ` mikpe at it dot uu dot se [this message]
2009-07-07 16:28 ` mikpe at it dot uu dot se
2009-07-07 19:05 ` jakub at gcc dot gnu dot org
2009-07-07 23:10 ` mikpe at it dot uu dot se
2009-07-08 16:43 ` mikpe at it dot uu dot se
2009-07-08 17:30 ` blp at cs dot stanford dot edu
2009-07-11 9:24 ` jakub at gcc dot gnu dot org
2009-07-11 9:26 ` jakub at gcc dot gnu dot org
2010-09-20 21:46 ` ebotcazou at gcc dot gnu dot org
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