Dear Mr. Haley: Thank you for your suggestions. I will read the materials at http://www.cellperformance.com/mike_acton/2006/06/understanding_strict_aliasing.html and try to find the bugs in my program. Thank you for very much your time and help. Wanxia Quoting Andrew Haley <aph@xxxxxxxxxx>: > Wei, Wanxia wrote: > > > My C program is a local search algorithm for solving SAT (Satisfiability problem). > The > > following is a brief description of this program. > > > > This program uses random integers to generate an initial assignment to a SAT > instance. > > Then, it chooses a variable by using a heuristic and then flips this variable > (flip > > means to change the value of a variable from 0 to 1 or from 1 to 0) in each search > > step. After many search steps, if the assignment satisfies the instance, this > program > > stops. If the assignment still does not satisfy the instance after many search > steps, > > this program stops after a predefined number of search steps. The number of search > > steps is what I call performance in my previous e-mail. In addition, this program > uses > > both static and dynamic allocations. > > > > When I ran the two executables with different options on some SAT instances, they > have > > different flip numbers (the parameters for these two executables are the same. For > > example, I use the same seed for them to generate initial assignments). I ran the > > executable generated by using â??gcc -m32 â??O3 â??lmâ?? on a wide range of > instance on > > different servers for more than 1 year but I never got any errors (such as core > dump). > > Well, this is hard. If your program behaves differently when > -fno-strict-aliasing is used then it's very likely that, yes, your > program has a bug. But for me to explain what -fno-strict-aliasing > does requires you to have a fairly good understanding of the C > language. There's a fairly good explanation at > http://www.cellperformance.com/mike_acton/2006/06/understanding_strict_aliasing.html > > In summary, > > "Dereferencing a cast of a variable from one type of pointer to a different type is > _usually_ in violation of the strict aliasing rule." > > Andrew. >
