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Re: CPS and RTL

From: Andy Wingo
Subject: Re: CPS and RTL
Date: Thu, 24 Jan 2013 11:35:43 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux)


On Thu 24 Jan 2013 10:28, Mark H Weaver <address@hidden> writes:

> The problem is that CPS fixes the order in which everything is
> evaluated, such as the order in which procedure arguments are
> evaluated, the order in which 'let' or 'letrec' initializers are
> evaluated, etc.  The fact that these orders are unspecified in the
> direct-style gives the compiler freedom to choose an order that
> generates the best code, and apparently this freedom can often result
> in significant gains.  Such ordering decisions must be made before the
> conversion to CPS.

Agreed with the sentiment; however, two points:

  * we can have a CPS with let / letrec / * operators that bind a number
    of values in unspecified order, and have a pass later that fixes
    their order.

  * code motion passes like CSE depend on effects analysis, and can
    often commute some operations

Anyway, violent agreement!



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