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From: John Levine <johnl@taugh.com>
Newsgroups: alt.folklore.computers,comp.os.linux.misc
Subject: Re: stacks are not hard, The joy of FORTRAN-like languages
Date: Fri, 4 Oct 2024 03:49:53 -0000 (UTC)
Organization: Taughannock Networks
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According to Peter Flass  <peter_flass@yahoo.com>:
>> The subroutine calling convention required the calling program
>> to pass a pointer to a register save area.  A recursive routine
>> would have to allocate a save area in each instance (and, of
>> course, free it before exiting).  If they wanted local variables,
>> they'd have to allocate and free them as well.
>
>Presumably local variables would be allocated together with the save area.
>All the assembler code I wrote used GETMAIN/FREEMAIN, then I had a
>head-slapping moment a few years ago when someone said “just allocate a big
>chunk of memory and allocate save areas from it to eliminate lots of SVCs.”
>Of course this only makes sense when your assembler code has lots of
>internal calls, not for small stand-alone subroutines.

That's essentially what PL/I did.  The save areas and local variables were
allocated from a big chunk of memory, and when it ran out, the subroutine
prolog called an internal PL/I routine to get a new chunk and chain them
together.  Read all about it here starting on page 158:

https://bitsavers.org/pdf/ibm/360/pli/C28-6594-4_PL1_F_Programmers_Guide_Nov68.pdf

And for the PL/I subset on the tiny 360/20, it starts on page 200:

https://bitsavers.org/pdf/ibm/360/model20/C33-6007-1_360-20_PLI_Dec68.pdf

I hear that Algol F did GETMAIN/FREEMAIN at every block or procedure
entry and exit.  Someone at Princeton hacked it to suballocate from
larger chunks and vastly improved runtime performance.
-- 
Regards,
John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly