@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
-@c 1999, 2000, 2001 Free Software Foundation, Inc.
+@c 1999, 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@cindex portability
@cindex GCC and portability
-The main goal of GCC was to make a good, fast compiler for machines in
-the class that the GNU system aims to run on: 32-bit machines that address
-8-bit bytes and have several general registers. Elegance, theoretical
-power and simplicity are only secondary.
+GCC itself aims to be portable to any machine where @code{int} is at least
+a 32-bit type. It aims to target machines with a flat (non-segmented) byte
+addressed data address space (the code address space can be separate).
+Target ABIs may have 8, 16, 32 or 64-bit @code{int} type. @code{char}
+can be wider than 8 bits.
GCC gets most of the information about the target machine from a machine
description which gives an algebraic formula for each of the machine's
instructions. This is a very clean way to describe the target. But when
the compiler needs information that is difficult to express in this
-fashion, I have not hesitated to define an ad-hoc parameter to the machine
-description. The purpose of portability is to reduce the total work needed
-on the compiler; it was not of interest for its own sake.
+fashion, ad-hoc parameters have been defined for machine descriptions.
+The purpose of portability is to reduce the total work needed on the
+compiler; it was not of interest for its own sake.
@cindex endianness
@cindex autoincrement addressing, availability
and the availability of autoincrement addressing. In the RTL-generation
pass, it is often necessary to have multiple strategies for generating code
for a particular kind of syntax tree, strategies that are usable for different
-combinations of parameters. Often I have not tried to address all possible
-cases, but only the common ones or only the ones that I have encountered.
-As a result, a new target may require additional strategies. You will know
+combinations of parameters. Often, not all possible cases have been
+addressed, but only the common ones or only the ones that have been
+encountered. As a result, a new target may require additional
+strategies. You will know
if this happens because the compiler will call @code{abort}. Fortunately,
the new strategies can be added in a machine-independent fashion, and will
affect only the target machines that need them.
projects / msp430-gcc.git / blobdiff