Bug 190154

Summary:	gcc 4.2.0 miscompiles bitfields
Product:	Gentoo Linux	Reporter:	Reimar Döffinger <Reimar.Doeffinger>
Component:	[OLD] Core system	Assignee:	Gentoo Toolchain Maintainers <toolchain>
Status:	RESOLVED FIXED
Severity:	major	CC:	loki_val
Priority:	High
Version:	2007.0
Hardware:	All
OS:	Linux
URL:	http://lists.mplayerhq.hu/pipermail/mplayer-cvslog/2007-August/030927.html
Whiteboard:
Package list:		Runtime testing required:	---
Attachments:	testcase that miscompiles for me

Description Reimar Döffinger 2007-08-25 08:27:03 UTC

Copied from URL:
For anything bigger than -O1 it gives this output:
> reimar at hokum ~ $ gcc -O2 bitbug.c -o bitbug
> reimar at hokum ~ $ ./bitbug 0 1
> vals: 0 0 1 0

output should be
> vals: 0 -1 1 0

If you can confirm that this is not only due to some breakage on my system, I think gcc 4.2.0 should be -amd64, since this is a quite trivial feature and it is completely broken.
I will attach the sample C file shortly.

Comment 1 Reimar Döffinger 2007-08-25 08:27:58 UTC

Created attachment 129116 [details]
testcase that miscompiles for me

Comment 2 Peter Alfredsen (RETIRED) gentoo-dev

2007-08-25 09:15:06 UTC

pa@loki ~ $ for optlevel in 0 1 2 s 3; do gcc -O${optlevel} bitbug.c -o bitbug&&./bitbug 0 1&&rm ./bitbug; done
vals: 0 -1 1 0
vals: 0 1 1 0
vals: 0 0 1 0
vals: 0 0 1 0
vals: 0 0 1 0

This is on i686-pc-linux-gnu gcc 4.2.0

Comment 3 SpanKY gentoo-dev

2007-08-25 09:16:11 UTC

this is already known and fixed in gcc-4.2.1

Comment 4 SpanKY gentoo-dev

2007-10-07 02:14:51 UTC

gcc-4.2.1 in the tree