Re: What is the meaning of an expression?

From	Thomas Koenig <tkoenig@netcologne.de>
Newsgroups	comp.compilers
Subject	Re: What is the meaning of an expression?
Date	2022-01-22 20:46 +0000
Organization	news.netcologne.de
Message-ID	<22-01-093@comp.compilers> (permalink)
References	(2 earlier) <22-01-066@comp.compilers> <22-01-067@comp.compilers> <22-01-068@comp.compilers> <22-01-069@comp.compilers> <22-01-071@comp.compilers>

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Christopher F Clark <christopher.f.clark@compiler-resources.com> schrieb:

> The second one was from my own experience working on the Alpha
> optimizer at DEC.  The C++ compiler was one of the last pieces of
> software to use the one based upon Fred Chow's work.  That was my
> responsibility at the time (the optimizer, not the C++ compiler).  In
> any case, the front end writers were very aggressive in inlining
> subroutines and doing whole-program optimization by that trick.

When to inline and when not to inline is still a major issue today.

> The result was very massive files of the intermediate representation.  The
> result, for certain large (and important) C++ programs the compiler
> would work for days before it had filled up all the paging space on
> the engineering cluster at DEC, which was multiple disks of paging and
> as a result crashed not only the compiler, but in some cases the
> entire cluster.   This made for some very unhappy users, because they
> had waited days and they still didn't get a successful compilation.

https://xkcd.com/303/ and https://dilbert.com/strip/1998-06-04
come to mind :-)


> Fortunately, a small amount of analysis on my part allowed me to
> realize that most of the optimizers data structures while N-squared in
> size, were actually filled with mostly zero values.

Quadratic algorithms (if in space or in time) are a progressively
bad idea.  Programs are getting bigger, and anybody who thinkis
a quadratic algrorithm is OK, will be hit sooner or later with a
(real-life) test case which brings it out into the open.

Just a random example:  Some time ago, a test case for gcc was
submitted which used up hours and Gigabytes for compiliation.
It consisted of a single basic block in a subroutine, with thousands
of variables and thousands of assignments (getting translated into
ten thousands of SSA statements).

This code was not written by a human, but by a computer algrebra
system expanding some complicated formula.

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What is the meaning of an expression? Roger L Costello <costello@mitre.org> - 2022-01-14 12:15 +0000
  Re: What is the meaning of an expression? anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2022-01-14 18:20 +0000
  Re: What is the meaning of an expression? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2022-01-15 00:28 +0100
  Re: What is the meaning of an expression? gah4 <gah4@u.washington.edu> - 2022-01-14 17:58 -0800
  Re: What is the meaning of an expression? George Neuner <gneuner2@comcast.net> - 2022-01-15 02:05 -0500
  Re: What is the meaning of an expression? "matt.ti...@gmail.com" <matt.timmermans@gmail.com> - 2022-01-15 06:21 -0800
    Re: What is the meaning of an expression? Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2022-02-03 12:50 +0000
  Re: What is the meaning of an expression? Jan Ziak <0xe2.0x9a.0x9b@gmail.com> - 2022-01-16 07:44 -0800
    Re: What is the meaning of an expression? Jan Ziak <0xe2.0x9a.0x9b@gmail.com> - 2022-01-17 15:45 -0800
      Re: What is the meaning of an expression? Jan Ziak <0xe2.0x9a.0x9b@gmail.com> - 2022-01-18 10:03 -0800
        Re: What is the meaning of an expression? gah4 <gah4@u.washington.edu> - 2022-01-18 15:18 -0800
          Re: What is the meaning of an expression? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2022-01-19 11:54 +0100
            Re: What is the meaning of an expression? Jan Ziak <0xe2.0x9a.0x9b@gmail.com> - 2022-01-19 09:17 -0800
              Re: What is the meaning of an expression? gah4 <gah4@u.washington.edu> - 2022-01-19 14:03 -0800
              Re: What is the meaning of an expression? Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2022-01-20 13:02 +0100
                Re: What is the meaning of an expression? dave_thompson_2@comcast.net - 2022-01-30 22:51 -0500
            Re: What is the meaning of an expression? Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2022-01-19 20:13 +0200
              Re: What is the meaning of an expression? Thomas Koenig <tkoenig@netcologne.de> - 2022-01-22 20:46 +0000
  Re: What is the meaning of an expression? Thomas Koenig <tkoenig@netcologne.de> - 2022-01-19 20:51 +0000

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