optimization/4888: incorrect code with -Ox, x >= 2

optimization/4888: incorrect code with -Ox, x >= 2

[jfran]

>Number:         4888
>Category:       optimization
>Synopsis:       incorrect code with -Ox, x >= 2
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 16 04:06:01 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     jfran
>Release:        gcc >=2.96 <=3.0.2
>Organization:
>Environment:

>Description:
With optimizations enabled, "f=x; y=*(type*)&f;" reads garbage 
on 'y' unless 'type'=='char' (problem with memory alias?) 

"f=x; g(); y=*(type*)&f;" works fine if g() is not
inlined.
>How-To-Repeat:
Compile with -O0, execute.
Compile with -O2, execute.
Uncomment the commented line.
Test again.
>Fix:

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

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Re: optimization/4888: incorrect code with -Ox, x >= 2

[rth]

The following reply was made to PR optimization/4888; it has been noted by GNATS.

From: rth@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  jfran@clip.dia.fi.upm.es, nobody@gcc.gnu.org
Cc:  
Subject: Re: optimization/4888: incorrect code with -Ox, x >= 2
Date: 27 Nov 2001 04:45:43 -0000

 Synopsis: incorrect code with -Ox, x >= 2
 
 State-Changed-From-To: open->closed
 State-Changed-By: rth
 State-Changed-When: Mon Nov 26 20:45:42 2001
 State-Changed-Why:
     Not a bug.  See ISO/IEC 9899:1999 Section 6.9 paragraph 7.
     
     In summary, you may not access an object with anything other
     than its proper type.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4888&database=gcc

Re: optimization/4888: incorrect code with -Ox, x >= 2

[rth]

Synopsis: incorrect code with -Ox, x >= 2

State-Changed-From-To: open->closed
State-Changed-By: rth
State-Changed-When: Mon Nov 26 20:45:42 2001
State-Changed-Why:
    Not a bug.  See ISO/IEC 9899:1999 Section 6.9 paragraph 7.
    
    In summary, you may not access an object with anything other
    than its proper type.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4888&database=gcc