Re: a practical UNCOL

David Keppel <>
13 May 89 12:57:26 GMT

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From: David Keppel <>
Newsgroups: comp.compilers
Summary: Impedance matching
Keywords: compiler ir rtl dag code generation
Date: 13 May 89 12:57:26 GMT
References: <>
Organization: U of Washington, Computer Science, Seattle

Ralph Johnson <> writes:
>[Fraser/Davidson RTL IR]
>[moderator: isn't that what gcc uses (successfully)?]

My compilers prof has pointed out to me that matching for
optimizations and instruction selection in an RTL (Fraser/Davidson,
IBM PL.801) is a special case of matching in a DAG (directed acyclic
graph) -structured ir (Graham/Glanville/Henry).

One important distinction is that all matching in an RTL is done at
the level of things that usually look like RISC machine instructions.
Thus the code quality is better when there is a good match between the
instructions in the machine-independent RTL and the instructions in
the physical hardware.

;-D on ( The code degenerator ) Pardo

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