c++/811: g++/i686-pc-linux-gnu: -O0 generate bad code (faulty temporary ?)

[homann@pb.izm.fhg.de]

>Number:         811
>Category:       c++
>Synopsis:       g++/i686-pc-linux-gnu: -O0 generate bad code (faulty temporary ?)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Nov 15 06:06:00 PST 2000
>Closed-Date:
>Last-Modified:
>Originator:     Ulrich Homann
>Release:        gcc-2.7.2.3 up to gcc-2.92.2 but not redhat gcc-2.96 (gcc-20001113 didn't work for me)
>Organization:
>Environment:
debian potato: linux 2.2.16, glibc 2.1.3
Pentium III
-- or --
Redhat 6? and AMD-K7
>Description:
Attached File miscompiles wenn disabling optimisation (-O0)
on Intel-PCs:

> g++ -O0 point_bug.cc -o point_bug && ./point_bug
p1: (3,4)  p2: (5,6)
((p1+p2)/2): (4,0)

> g++ -O1 point_bug.cc -o point_bug && ./point_bug
p1: (3,4)  p2: (5,6)
((p1+p2)/2): (4,5)

Introducing an explizit temporary avoid this Problem:
Point tmp=p1+p2; tmp/=2;
>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/x-c++src; name="point_bug.cc"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="point_bug.cc"

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