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Re: regclass oddity?

From: Jim Wilson <wilson at specifix dot com>
To: Dave Korn <dave dot korn at artimi dot com>
Cc: gcc at gcc dot gnu dot org
Date: Thu, 15 Mar 2007 13:18:53 -0700
Subject: Re: regclass oddity?
References: <011901c7671a$1234f6a0$2e08a8c0@CAM.ARTIMI.COM>

Dave Korn wrote:

  When regclass determines that placing an operand into either one of several
register classes would have the same cost, it picks the numerically highest
one in enum reg_class ordering.

One possible solution is to give the special registers a higher REGISTER_MOVE_COST to discourage their use.

Another solution is to use ! and ? in the constraints to increase the cost of alternatives that are inconvenient.

There is also CLASS_LIKELY_SPILLED_P which is supposed to discourage local-alloc from using registers in single-reg classes. At least there is code for this in gcc-2.95.3. It looks like things have changed in this area since then. -- Jim Wilson, GNU Tools Support, http://www.specifix.com

References:
- regclass oddity?
  - From: Dave Korn

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