Path: utzoo!utgpu!water!watmath!clyde!rutgers!sri-spam!ames!oliveb!intelca!mipos3!td2cad!cpocd2!howard
From: howard@cpocd2.UUCP (Howard A. Landman)
Newsgroups: comp.arch
Subject: Re: taken -vs- untaken branches, Fo
Message-ID: <1070@cpocd2.UUCP>
Date: 19 Jan 88 22:06:17 GMT
References: <839@ima.ISC.COM> <28200085@ccvaxa> <38390@sun.uucp>
Reply-To: howard@cpocd2.UUCP (Howard A. Landman)
Organization: Intel Corp. ASIC Systems Organization, Chandler AZ
Lines: 22

In article <38390@sun.uucp> ram@sun.UUCP (Renu Raman, Sun Microsystems) writes:
>     Any day, programmer "over-drive" is better (any examples to the
>     contrary?).

Sure.  I once profiled some code that was spending about 90% of its time in
one routine.  The original programmer had gone in and made several variables
"register" variables, but had made a bad choice of which ones.  I got a 12%
speedup or so by REMOVING one "register" declaration, allowing the compiler
the freedom to select its own.  In fact, removing ALL the register declarations
sped the routine up nearly as much.  I suspect that the many C compilers which
ignore register declarations do so because of incidents like this (plus a
little laziness, possibly).

In the hands of an extremely competent programmer, with a desperate need for
performance, over-drive is sometimes better.  But assembly is even better for
those rare cases, so why bother?

-- 
	Howard A. Landman
	{oliveb,hplabs}!intelca!mipos3!cpocd2!howard
	howard%cpocd2.intel.com@RELAY.CS.NET
	One hand clapping sounds a lot like two hands clapping, only quieter.