optimization/10774: Problem with ``-march=pentium4 -O''

[mi+gcc@aldan.algebra.com]

>Number:         10774
>Category:       optimization
>Synopsis:       Problem with ``-march=pentium4 -O''
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Wed May 14 00:26:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Mikhail Teterin
>Release:        gcc version 3.2.2
>Organization:
>Environment:
Reproduceable with:
	gcc version 3.2.2 [FreeBSD] 20030205 (release)
	gcc version 3.2 20020903 (Red Hat Linux 8.0 3.2-7)
>Description:
The attached file (you can remove the ``#include <stdio.h>'' line if you
insist) gets miscompiled with ``-march=pentium4 -O''. Removing the -O
or specifying another architecture (such as pentium3) fixes the problem.

The expected result is 0.5. But an optimized for pentium4 version
produces 5.29463e-315 (same value on both Linux and FreeBSD).
According to the debugger, the 22-nd line is skipped in the P4 case.

See also the FreeBSD problem reports:
	http://www.FreeBSD.org/cgi/query-pr.cgi?pr=bin/43299
	http://www.FreeBSD.org/cgi/query-pr.cgi?pr=i386/51210

	

>How-To-Repeat:
% cc -O1 -march=pentium4 simple_pow.c -Wall && ./a.out
7.000000 ^ 2.100000
7.000000 ^ 2.100000
ax is 5.29463e-315
result is 5.29463e-315
% cc -O1 -march=pentium3 simple_pow.c -Wall && ./a.out
7.000000 ^ 2.100000
7.000000 ^ 2.100000
ax is 0.5
result is 0.5
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
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Content-Disposition: attachment; filename="simple_pow.c"

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