Re: Data Structure Reorganizing Optimizations

Andy Glew <glew@ichips.intel.com> wrote:
}Lebeck and Wood's CPROF paper
} Alvin R. Lebeck and David A. Wood, "Cache Profiling and the
} SPEC Benchmarks: A Case Study," IEEE Computer, October 1994.
}discusses, among other things, optimizations that aren't quite legal
}in C: rearranging data structures, such as structure element order,
}converting array of structs to structs or arrays, etc.
    ...
}I believe that C's rules about data structure organization are
}obsolete. Certainly, they are not in the ken of the usual programmer
}using C or C++. Why not permit compilers to do such "illegal" data
}structure reorganizations, bringing the performance gains Lebeck and
}Wood describes to the standard application?


Perhaps a "struct" should be paddable and/or reorganizable
and a "packed struct" should not.


struct blah { packed struct udphdr {
char thing; uint16 sport,dport;
int thang; uint16 dport;
char thong; uint16 cksum;
}; };


John
--
John Hascall
Systems Software Engineer
Project Vincent
Iowa State University Computation Center + Ames, IA 50011 + 515/294-9551


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