Re: Using C as a back end

engler@Stanford.EDU (Dawson R Engler)
31 Oct 2000 14:40:40 -0500

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From: engler@Stanford.EDU (Dawson R Engler)
Newsgroups: comp.compilers
Date: 31 Oct 2000 14:40:40 -0500
Organization: Stanford University, CA 94305, USA
References: 00-10-148 00-10-154 00-10-212
Keywords: C
Posted-Date: 31 Oct 2000 14:40:40 EST

>[You can get the effect of a computed goto in standard C using a
>switch full of goto's, and any decent compiler should generate about
>the same code as for an explicit computed goto, so I don't see that
>particular wart as a major one. -John]


Last time I checked the difference was about 2x (admittedly this
was about four years ago). Two reasons for the overhead:
1. switch does a bounds check.


2. case arm ``breaks'' will jump back to the top of the
switch, rather than cutting through to exactly where you want
to go.


For writing fast threaded interpreters, computed goto is a good thing.

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