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From: ram@wb1.cs.cmu.edu (Rob MacLachlan)
Newsgroups: comp.arch
Subject: Re: Compile Times on BIG Basic Blocks
Message-ID: <9124@pt.cs.cmu.edu>
Date: 2 May 90 13:12:03 GMT
References: <7942@granola.ai.mit.edu>
Organization: Carnegie-Mellon University, CS/RI
Lines: 15


It's pretty silly to get worked up about compiler algorithms that perform
badly on large basic blocks; all large blocks means is that the program is
very simple, giving the optimizers an embarassment of riches.

If these algorithms really were optimal, and if it really were important to
extend optimality across as large an extent of the program as possible, then
there might be some reason for concern.  However neither is true.  All you
need to do is limit the extent of the intra-block optimization, either with
a window or by gratuitously splitting blocks.

The really nasty problems in flow analysis are those which blow up with
program *complexity*, not simplicitly.

  Rob