optimization/2560: Optimization cause wrong result

[c_huang@21cn.com]

>Number:         2560
>Category:       optimization
>Synopsis:       Optimization cause wrong result
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Apr 16 09:16:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     c_huang@21cn.com
>Release:        gcc 2.96
>Organization:
>Environment:
RedHat LINUX 7.0 on HP Vectra XU, Pro 200, 64M
>Description:
Optimization level 3 will cause to get wrong result. However, if you change to level 2 or modify the sentense, you will get right results
>How-To-Repeat:
------wrong result-----
$ gcc -O3 tt.cpp -o tt -D makeerr=1
$ ./tt
64 bits: 00005CBA9063FC00 101956356144128

32 bits low: 9063FC00 2422471680

32 bits high 00005CBA    23738

996 Days 21:3:10           <------wrong
clk=4000000 CPS=1000000
CPU clock = 199463975
-----right result-----
$ gcc -O3 tt.cpp -o tt -D makeerr=0
$ ./tt
64 bits: 00005CBB1F9C75AA 101958758987178

32 bits low: 1F9C75AA 530347434

32 bits high 00005CBB    23739

5 Days 21:51:10            <-----right
clk=4010000 CPS=1000000
CPU clock = 199656522
-----right result-----
$ gcc -O2 tt.cpp -o tt -D makeerr=1
$ ./tt
64 bits: 00005CEB7D3B0089 102166488088713

32 bits low: 7D3B0089 2101018761

32 bits high 00005CEB    23787

5 Days 22:12:4             <-----right
clk=4010000 CPS=1000000
CPU clock = 199573463
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: