Re: optimization/4570: error reading bytes from double variable

Re: optimization/4570: error reading bytes from double variable

[aoliva]

Synopsis: error reading bytes from double variable

State-Changed-From-To: open->closed
State-Changed-By: aoliva
State-Changed-When: Sun Nov 25 08:45:58 2001
State-Changed-Why:
    Not a bug.  GCC is allowed by the aliasing rules in the C Standard to assume an int* can't possibly point to the same memory as e, that has type double.  If you depend on this behavior, use -fno-strict-aliasing, or access the storage using pointers to char, that can alias anything.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4570&database=gcc

Re: optimization/4570: error reading bytes from double variable

[aoliva]

The following reply was made to PR optimization/4570; it has been noted by GNATS.

From: aoliva@gcc.gnu.org
To: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  nobody@gcc.gnu.org, philippe_ribet@hotmail.com
Cc:  
Subject: Re: optimization/4570: error reading bytes from double variable
Date: 25 Nov 2001 16:45:59 -0000

 Synopsis: error reading bytes from double variable
 
 State-Changed-From-To: open->closed
 State-Changed-By: aoliva
 State-Changed-When: Sun Nov 25 08:45:58 2001
 State-Changed-Why:
     Not a bug.  GCC is allowed by the aliasing rules in the C Standard to assume an int* can't possibly point to the same memory as e, that has type double.  If you depend on this behavior, use -fno-strict-aliasing, or access the storage using pointers to char, that can alias anything.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4570&database=gcc

optimization/4570: error reading bytes from double variable

[philippe_ribet]

>Number:         4570
>Category:       optimization
>Synopsis:       error reading bytes from double variable
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Oct 15 02:06:02 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     philippe_ribet@hotmail.com
>Release:        gcc version 3.0.2 20010922
>Organization:
>Environment:
Athlon processor
>Description:
gcc-3.0.1 give good result up to -O2, bad one with -O3
gcc-3.0.2 give good result without optimization, bad with -O2
May be relative to optimization recently moved from -O3 to -O2.

main()
{
  double e=0;
  e=(double)(0.5);
  printf("e=%08x%08x\n",*((int *)(((char *)(&e)))),*((int *)(((char *)(&e))+4)));
}

>How-To-Repeat:

>Fix:

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