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

[Carlos O'Donell]

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

From: Carlos O'Donell <carlos@baldric.uwo.ca>
To: bangerth@dealii.org, 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 16:23:05 -0500

 > State-Changed-From-To: open->feedback
 > State-Changed-By: bangerth
 > State-Changed-When: Fri Dec  6 13:01:29 2002
 > State-Changed-Why:
 >     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?
 
 Unsigned overflow is defined. It is GCC's inconsistent
 implementation-dependant conversion that is causing the problem.
 
 "The comparison is between to signed values that gcc
 must convert. This conversion is implementation-dependant.
 As such, the implementation-dependant behaviour cannot
 be optimized away and must remain consistent across
 optimization levels." - Carlos
 
 c.