mercury/runtime/machdeps

This directory contains architecture-dependent code
for using gcc global register variables.

Each header file in this directory should implement the same
interface; this interface is documented in the file `no_regs.h'
(which is the portable version that gets used for unknown
architectures, or if you're not using gcc).

To add a definition for a new architecture, you need to

	- Find the config header file in the gcc source code which
	  defines how registers are used for that machine
	  (e.g. for mips, the file is .../config/mips/mips.h).
	  Find the definitions of FIXED_REGISTERS and
	  CALL_USED_REGISTERS in that header file.
	  These are arrays of booleans indexed by register
	  number; somewhere in the same file there should also be
	  some indication of gcc's register numbering scheme,
	  so that you can figure out the corresponding register names.

	- Choose which registers for Mercury to use as global register
	  variables.  Registers that are fixed or call_used cannot be used.
	  (That's why you need to look at the FIXED_REGISTERS and
	  CALL_USED_REGISTERS macros in the gcc source code.)
	  It's a good idea to leave some registers for use by gcc
	  (but that may not always be possible, e.g. see the comment
	  at the start of alpha_regs.h).
	  Other than that, it's up to you.

	- Add a new header file for your architecture in this directory.
	  This header file should define the same set of macros as the
	  other header files here.  The documentation for what they
	  should do is in `no_regs.h'.

	- Add a new case to the switch on machine type in `../regs.h';
	  this new case should #include the header file you just added.

	- Add the new header file to the MACHHDRS list in runtime/Mmakefile.