Re: optimization/7799: [3.2/3.3 regression] Loop bug with optimization flag -Os in gcc

[Joern Rennecke <amylaar@onetel.net.uk>]

The following reply was made to PR optimization/7799; it has been noted by GNATS.

From: Joern Rennecke <amylaar@onetel.net.uk>
To: segher@koffie.nl (Segher Boessenkool)
Cc: ehrhardt@mathematik.uni-ulm.de (Christian Ehrhardt),
        nejataydin@superonline.com, gcc-gnats@gcc.gnu.org, gcc@gcc.gnu.org,
        gcc-bugs@gcc.gnu.org
Subject: Re: optimization/7799: [3.2/3.3 regression] Loop bug with optimization flag -Os in gcc
Date: Fri, 20 Dec 2002 06:17:18 +0000 (GMT)

 > 6.2.5.19:
 >         ... An array type describes a contiguously allocated nonempty set of
 >         objects with a particular member object type, called the element
 >         type. ...
 >
 > So an array can not wrap around address 0.
 
 It can't wrap around there, but if pointers are signed, it might straddle 0
 nonetheless.  This requires, of course, for an aligned start address
 that the address 0 is not the same as NULL, which AFAICR is something gcc
 doesn't currently support.
 
 OTOH, if the start address is not aligned to a multiple of the types size,
 you can have the array straddle address 0 without it ever being a valid
 address.  Well, that is if character pointers have a different
 representation ;-)