Path: utzoo!attcan!uunet!husc6!ukma!gatech!mcnc!rti!sas!toebes
From: toebes@sas.UUCP (John Toebes)
Newsgroups: comp.sys.amiga
Subject: Re: C versus Assembly, which one?
Message-ID: <554@sas.UUCP>
Date: 20 Jun 88 04:57:20 GMT
References: <1968@uhccux.uhcc.hawaii.edu> <4508@killer.UUCP>
Reply-To: toebes@sas.UUCP (John Toebes)
Organization: SAS Institute Inc, Cary NC
Lines: 43

In article <4508@killer.UUCP> elg@killer.UUCP (Eric Green) writes:
>On a related topic, does the Lattice 4.0 compiler do any (useful)
>optimizations besides common subexpression? In particular, some of the RISC
>compilers generate code that keep calculated addresses around, and all of the
>RISC compilers seem to make every attempt to keep most-common-used variables
>in registers (in fact, the Pyramid 90x compiler totally ignores the "register"
>declarators, as far as I can tell -- at least, when you have fewer than 16
>local variables and 16 parameters).
>
>I've been looking at the code generated by the Manx 3.60 compiler, and it
>looks pretty simplistic. Does Lattice 4.0 manage any better?
>
The Lattice 4.0 compiler has a fairly complex code generation scheme with
both a forward and backward look at the code being processed.  It performs:
  a) Common sub-expression elimination (over more than a simple basic block)
  b) dead code elimination (usually :-)
  c) Register tracking
  d) Condition code tracking
  e) conversion compression (int=>short = short=>int + short=>int as
     short = short+short)
  f) Optimized builtin functions
  g) common string elimination
  h) constant folding
  i) branch to branch supression
  j) indexing subsumption
  k) [my favorite because I thought it up] forward register merging across
     if/then/else statements and other nonsense.
In addition, there is quite a bit of analysys involved with register tracking
and selection making it much more complex than a simplistic pattern matching
code generator often found with PCC and its derivatives. (No cut intended)

Even with all it does currently, I am not yet satisfied (maybe I will never
be) so this list constantly grows.

>(& onrelated topic, SDB gurus my machine regularly, sigh).
Have you called their tech support?  That's what you pay for when you get
a language product.
>Eric Lee Green    ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg

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