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From: shankar@hpclscu.HP.COM (Shankar Unni)
Newsgroups: comp.sys.hp
Subject: Re: gcc compiler (GNU C++) Where do we get it ?
Message-ID: <1340151@hpclscu.HP.COM>
Date: 16 Oct 90 03:06:42 GMT
References: <121@bwilab3.UUCP>
Organization: Hewlett-Packard Calif. Language Lab
Lines: 20

> What is *much* better code? Could you elaborate on why the code is much
> better?

Well, for one thing, HP-PA having such an interesting instruction set,
optimizers have to work very hard indeed to generate good code on it.  Just
an example: When generating code for a switch, the HP optimizer hoists the
first instruction of the block of code for a label to the shadow of the
branch to that block. Gcc does not. Similarly, the HP optimizer performs
many branch optimizations and peephole transformations that Gcc does not.

I'm not trying to put down Gcc in any way - it's just that Gcc/800 is too
new to have acquired the full bag of tricks that the HP optimizer (which
operates mostly at the machine instruction level, using aliasing
information generated from the front-ends) uses.

We have seen benchmarks in which the HP optimizer achieves as much as a 30%
improvement over Gcc in code size.  However, I know that the Utah folks are
grinding away at Gcc even now..
----
Shankar Unni.