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optimization/6164: incorrect code above optimization -O1


>Number:         6164
>Category:       optimization
>Synopsis:       incorrect code above optimization -O1
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Wed Apr 03 17:06:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Robert Sanders
>Release:        gcc 3.0.4
>Organization:
>Environment:
System: Linux rmsibook.zai.com 2.4.10-12a #1 Tue Oct 9 04:49:39 EDT 2001 ppc unknown	
Architecture:ppc
>Description:
The program is to test functions that convert between the VAX D double precision datatype and the IEEE double precision datatype (assuming a big-endian host).  The executable produces incorrect results for optimization levels above -O1.

The program will show the 8 bytes of the VAX double precision number, the resultant IEEE value, the 8 bytes of the IEEE double precision number, then convert back to the VAX double and show the 8 bytes.  If it doesn't get what it started with a message is displayed.
>How-To-Repeat:
This works:
	compile ->  gcc -Wall myc.c -o myc
	execute ->  ./myc
     ...
     compile ->  gcc -Wall -O1 myc.c -o myc
     execute ->  ./myc

These produce incorrect executable code
     compile -> gcc -Wall -O2 myc.c -o myc
     execute -> ./myc
     ...
     and so on thru compiling with -O5

NOTE:  We have seen a very similar problem on a Athelon Linux box under Redhat 7.x  *except* the the incorrect code only
appears with running with optimization level -O2.  The problem existed with gcc 3.0.3 as well.
>Fix:

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