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    SubjectRe: gcc 2.95 vs 3.21 performance
    On 4 February 2003 01:31, Richard B. Johnson wrote:
    > On Mon, 3 Feb 2003, Martin J. Bligh wrote:
    > > People keep extolling the virtues of gcc 3.2 to me, which I'm
    > > reluctant to switch to, since it compiles so much slower. But
    > > it supposedly generates better code, so I thought I'd compile
    > > the kernel with both and compare the results. This is gcc 2.95
    > > and 3.2.1 from debian unstable on a 16-way NUMA-Q. The kernbench
    > > tests still use 2.95 for the compile-time stuff.
    > [SNIPPED tests...]

    What was the size of uncompressed kernel binaries?
    This is a simple (and somewhat inaccurate) measure of compiler
    improvement ;)

    > Don't let this get out, but egcs-2.91.66 compiled FFT code
    > works about 50 percent of the speed of whatever M$ uses for
    > Visual C++ Version 6.0 I was awfully disheartened when I

    Yes. M$ (and some other compilers) beat GCC badly.

    > found that identical code executed twice as fast on M$ than
    > it does on Linux. I tried to isolate what was causing the
    > difference. So I replaced 'hypot()' with some 'C' code that
    > does sqrt(x^2 + y^2) just to see if it was the 'C' library.
    > It didn't help. When I find out what type (section) of code
    > is running slower, I'll report. In the meantime, it's fast
    > enough, but I don't like being beat by M$.

    I'm afraid it's code generation engine. It is just worse than
    M$ or Intel's one. It is not easily fixable,
    GCC folks have tremendous task at hand.

    I wonder whether some big companies supposedly supporting
    Linux (e.g. Intel) can help GCC team (for example by giving
    away some code and/or developer time).
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