Re: Gnu C compiler RTL question (Walter Misar)
18 Sep 1998 23:15:37 -0400

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From: (Walter Misar)
Newsgroups: comp.compilers
Date: 18 Sep 1998 23:15:37 -0400
Organization: main(){int i;for(i=0;i<3;i++)putchar(84+i*(10-9*i));}
References: 98-09-034
Keywords: GCC, question writes:
|> I read somewhere that the RTL is independent of the machine description, but
|> looking at some compiled code shows that it does depend on the registers used
|> as the stack and frame pointers.
|> Are thes the only instances where this occurs??

No, while the RTL language is independant of the machine description, RTL code
heavily depends on it.

From the "Using and Porting GNU CC" document:
> People frequently have the idea of using RTL stored as text in a file as an
> interface between a language front end and the bulk of
> GNU CC. This idea is not feasible.
> GNU CC was designed to use RTL internally only. Correct RTL for a given
> program is very dependent on the particular target
> machine. And the RTL does not contain all the information about the program.
> The proper way to interface GNU CC to a new language front end is with
> the "tree" data structure. There is no manual for this data
> structure, but it is described in the files `tree.h' and `tree.def'.
( see

Walter Misar

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