Performance Regressions; Previously: Death by error checks. (Christopher Glaeser)
28 Dec 1995 11:34:19 -0500

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From: (Christopher Glaeser)
Newsgroups: comp.compilers
Date: 28 Dec 1995 11:34:19 -0500
Organization: Compilers Central
References: 95-10-103 95-12-113
Keywords: performance

Henry Baker <> writes:

> Unfortunately, whereas before, he could rely upon the compiler staying
> just about as stupid from release to release, he now has to contend
> with compilers that get 'smarter' from release to release.

While it is true that many compilers continue to improve with each
release, the *implication* that the performance of a new release is
monotonically non-decreasing is false. It is not uncommon for new
compiler releases to have a ratio of performance improvements versus
performance regressions of about three to one.

Of course, SPEC performance is always monotonically non-decreasing,
even if the release must be postponed. It is possible that a code
fragment of a SPEC benchmark runs slower, but it must be offset by a
code fragment that improves by equal or greater amount, since the
emphasis is on the total sum gain.

Best regards,
Christopher Glaeser
Nullstone Corporation


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