Re: optimization/7726: Fails to produce the correct implementation-dependant output for loop optimization under x86 -> optimizes away a loop that should complete

[Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>]

The following reply was made to PR optimization/7726; it has been noted by GNATS.

From: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>
To: <bangerth@dealii.org>, <carlos@baldric.uwo.ca>, <gcc-bugs@gcc.gnu.org>,
   <gcc-prs@gcc.gnu.org>, <nobody@gcc.gnu.org>, <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: Re: optimization/7726: Fails to produce the correct implementation-dependant
 output for loop optimization under x86 -> optimizes away a loop that should
 complete
Date: Fri, 6 Dec 2002 22:22:46 +0100 (CET)

 On 6 Dec 2002 bangerth@dealii.org wrote:
 
 > Hm, the code goes into an endless loop on my system also without
 > optimization and with all the compilers I have (i.e. gcc2.95, 3.0,
 > 3.2, 3.2.2pre, 3.3pre, and icc7). Are you sure that the overflow you
 > are exploiting is really defined in ISO C?
 
 Reading the value of a union member other than the last one stored into is
 undefined (at least in C99), so it could be easily argued that this is not
 a bug. However, gcc seems to support this in some other places (see the
 info entry about aliasing). So IMHO this should either be "fixed", or it
 should be documented exactly which union type punning tricks are OK.
 
 	Falk