Re: Absolute beginner - Need some pointers

glen herrmannsfeldt <gah@ugcs.caltech.edu>
Wed, 05 Mar 2008 09:07:43 -0800

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From: glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups: comp.compilers
Date: Wed, 05 Mar 2008 09:07:43 -0800
Organization: Compilers Central
References: 08-02-091 08-03-008 08-03-013 08-03-022
Keywords: Fortran, history, design, comment
Posted-Date: 05 Mar 2008 21:05:02 EST

Anton Ertl wrote:
(snip)


> Yes, most VMs implement control flow using assembler-style VM branch
> instructions. You don't need backpatching for backward branches
> (e.g., the loop-back branch you mentioned), because in that case you
> know where you want to branch to when you generate the branch.


Fortran up through Fortran 66 allows the test to be done at the end of
the loop. That is, the statements inside the loop are executed at
least once. I believe this is due to the indexing and branching
instructions on the 704, and not that it made code generation easier,
but it would tend to avoid the forward branch that would otherwise be
needed.


-- glen
[The code was smaller, which was a big deal back then. -John]


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