Submitter-Id: net
Originator: Pierre Lombard
Synopsis: wrongcode when optimizing mmx asm inline
Severity: serious
Priority: medium
Confidential: no
Category: optimization
Class: wrong-code
Release: 3.0.3 (Debian testing/unstable)
Environment:
System: Linux s41 2.4.17 #2 SMP Sat Dec 29 12:34:41 CET 2001 i686 unknown
Architecture: i686
<machine, os, target, libraries (multiple lines)>
host: i386-pc-linux-gnu
build: i386-pc-linux-gnu
target: i386-pc-linux-gnu
configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,proto,objc --prefix=/usr
--infodir=/share/info --mandir=/share/man --enable-shared --with-gnu-as
--with-gnu-ld --with-system-zlib --enable-long-long --enable-nls
--without-included-gettext --disable-checking --enable-threads=posix
--enable-java-gc=boehm --with-cpp-install-dir=bin --enable-objc-gc i386-linux
Description:
I had already filed a bug report in July 2001 but there was neither follow-up
nor reply. It's archived here:
http://gcc.gnu.org/ml/gcc-bugs/2001-07/msg00910.html.
With -O0 (correct code - ok with -O1 too):
...
.section .rodata
.align 8
.type mm_wabs,@object
.size mm_wabs,8
mm_wabs:
.value 65535
.value 65535
.value 65535
.value 65535
.align 8
.type mm_wone,@object
.size mm_wone,8
mm_wone:
.value 1
.value 1
.value 1
.value 1
.text
.align 4
.type dct_unquantize,@function
...
#APP
movd 20(%ebp), %mm6
punpckldq %mm6, %mm6
movq mm_wabs, %mm4 //XXX
movq %mm6, %mm7
movq mm_wone, %mm5 //XXX
packssdw %mm6, %mm7
pxor %mm6, %mm6
.p2align 2
#NO_APP
...
With -O2 (and above => the same problem appears):
.Lfe6:
.size draw_edges,.Lfe6-draw_edges
.section .rodata
.align 8
.type mm_wabs,@object
.size mm_wabs,8
mm_wabs:
.value 65535
.value 65535
.value 65535
.value 65535
.align 8
.type mm_wone,@object
.size mm_wone,8
mm_wone:
.value 1
.value 1
.value 1
.value 1
.align 2
.LC113:
.value 1
.align 2
.LC114:
.value 65535
.text
.align 4
.type dct_unquantize,@function
...
#APP
movd %edi, %mm6
punpckldq %mm6, %mm6
movq .LC114, %mm4 // XXX
movq %mm6, %mm7
movq .LC113, %mm5 // XXX
packssdw %mm6, %mm7
pxor %mm6, %mm6
#NO_APP
...
I still think mm4 and mm5 are not initialized to the same values -O0 and -O2
with 3.0.3. Can somebody confirm it's a bug (or explain me why it is not) ?
How-To-Repeat:
Just compile it with: gcc-3.0 -O[02] -S mpegvideo.i
The preprocesses file has already been uploaded:
http://gcc.gnu.org/ml/gcc-bugs/2001-07/msg00910/mpegvideo.i.gz
Fix:
A workaround is to use a 64bits unsigned long long.
Another one is to compile with -O0.
