133 lines
3.9 KiB
Text
133 lines
3.9 KiB
Text
.\" $Header$
|
|
.TL
|
|
Addition of register variables to an existing table.
|
|
.NH 1
|
|
Introduction
|
|
.PP
|
|
This is a short description of the newest feature in the
|
|
table driven code generator for the Amsterdam Compiler Kit.
|
|
It describes how to add register variables to an existing table.
|
|
This assumes you have the distribution of October 1983 or later.
|
|
It is not clear whether you should read this when starting with
|
|
a table for a new machine,
|
|
or whether you should wait till the table is well debugged already.
|
|
.NH 1
|
|
Modifications to the table itself.
|
|
.NH 2
|
|
Register section
|
|
.PP
|
|
You can add just before the properties of the register one
|
|
of the following:
|
|
.IP - 2
|
|
regvar
|
|
.IP -
|
|
regvar ( pointer )
|
|
.IP -
|
|
regvar ( loop )
|
|
.IP -
|
|
regvar ( float )
|
|
.LP
|
|
All register variables of one type must be of the same size,
|
|
and they may have no subregisters.
|
|
.NH 2
|
|
Codesection
|
|
.PP
|
|
.IP - 2
|
|
Two pseudo functions are added to the list allowed inside expressions:
|
|
.RS
|
|
.IP 1) 3
|
|
inreg ( expr ) has as a parameter the offset of a local,
|
|
and returns 0,1 or 2:
|
|
.RS
|
|
.IP 2: 3
|
|
if the variable is in a register.
|
|
.IP 1:
|
|
if the variable could be in a register but isn't.
|
|
.IP 0:
|
|
if the variable cannot be in a register.
|
|
.RE
|
|
.IP 2)
|
|
regvar ( expr ) returns the register associated with the variable.
|
|
Undefined if it is not in a register.
|
|
So regvar ( expr ) is defined if and only if inreg (expr ) == 2.
|
|
.RE
|
|
.IP -
|
|
It is now possible to remove() a register expression,
|
|
this is of course needed for a store into a register local.
|
|
.IP -
|
|
The return out of a procedure may now involve register restores,
|
|
so the special word 'return' in the table will invoke a user defined
|
|
function.
|
|
.NH 1
|
|
Modifications to mach.c
|
|
.PP
|
|
If register variables are used in a table, the program
|
|
.I cgg
|
|
will define the word REGVARS during compilation of the sources.
|
|
So the following functions described here should be bracketed
|
|
by #ifdef REGVARS and #endif.
|
|
.IP - 2
|
|
regscore(off,size,typ,freq,totyp) long off;
|
|
.br
|
|
This function should assign a score to a register variable,
|
|
the score should preferably be the estimated number of bytes
|
|
gained when it is put in a register.
|
|
Off and size are the offset and size of the variable,
|
|
typ is the type, that is reg_any, reg_pointer, reg_loop or reg_float.
|
|
Freq is the number of times it occurs statically, and totyp
|
|
is the type of the register it is planned to go into.
|
|
.br
|
|
Keep in mind that the gain should be net, that is the cost for
|
|
register save/restore sequences and the cost of initialisation
|
|
in the case of parameters should already be included.
|
|
.IP -
|
|
i_regsave()
|
|
.br
|
|
This function is called at the start of a procedure, just before
|
|
register saves are done.
|
|
It can be used to initialise some variables if needed.
|
|
.IP -
|
|
f_regsave()
|
|
.br
|
|
This function is called at end of the register save sequence.
|
|
It can be used to do the real saving if multiple register move
|
|
instructions are available.
|
|
.IP -
|
|
regsave(regstr,off,size) char *regstr; long off;
|
|
.br
|
|
Should either do the real saving or set up a table to have
|
|
it done by f_regsave.
|
|
Note that initialisation of parameters should also be done,
|
|
or planned here.
|
|
.IP -
|
|
regreturn()
|
|
.br
|
|
Should restore saved registers and return.
|
|
The function result is already in the function return area by now.
|
|
.NH 1
|
|
Examples
|
|
.PP
|
|
Here are some examples out of the PDP 11 table
|
|
.DS
|
|
lol inreg($1)==2| | | regvar($1) | |
|
|
|
|
lil inreg($1)==2| | | {regdef2, regvar($1)} | |
|
|
|
|
stl inreg($1)==2| xsource2 |
|
|
remove(regvar($1))
|
|
move(%[1],regvar($1)) | | |
|
|
|
|
inl inreg($1)==2| | remove(regvar($1))
|
|
"inc %(regvar($1)%)"
|
|
setcc(regvar($1)) | | |
|
|
.DE
|
|
.NH 1
|
|
Afterthoughts.
|
|
.PP
|
|
At the time of this writing the tables for the PDP 11 and the M68000 and
|
|
the VAX are converted, in all cases the two byte wordsize versions.
|
|
No big problems have occurred, but experience has shown that it is
|
|
necessary to check your table carefully for all patterns with locals in them
|
|
because if you forget one code will be generated by that one coderule
|
|
to use the memoryslot the local is not in.
|
|
|