Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!samsung!aplcen!haven!udel!mmdf
From: HBO043%DJUKFA11.BITNET@cunyvm.cuny.edu (Christoph van Wuellen)
Newsgroups: comp.os.minix
Subject: Re: Minix needs a C compiler with source
Message-ID: <11760@nigel.udel.EDU>
Date: 21 Feb 90 10:38:11 GMT
Sender: mmdf@udel.EDU
Lines: 21

To those who write a new code generator (68000) for the ACK compiler:

Recently I tuned a code generator for an 68000 C-compiler and so I expect
a leap of 150..200 Dhrystones/sec from the following single change:

- There is frequently the situation of multiplying two longs which were
  cast from short. The discussion on the speedup by changin _mli.s makes
  clear how important this pattern is (e.g. with pointer additions)
  I found it trivial to map this on a 68000 muls instruction, avoiding
  a library call (there is a similar pattern for the mulu instruction).

This change let my compiler jump from 850 to 1000 dhrystones, an optimal
structure assignment strategy let it jump from 700 to 850 dhrystones (but
structure assignments are not that important outside of dhrystone).

So only in the case the guy hacking on a new code generator could miss this
will he (she?) take care of muls instructions?

(The code generator is the only place where to do it since it is the only
part that knows about CPU instructions)
/Christoph van Wuellen