@c Copyright (C) 2000 Red Hat, Inc.
@c This file is part of the CGEN manual.
@c For copying conditions, see the file cgen.texi.

@node Preprocessor macros
@chapter Preprocessor macros
@cindex Preprocessor macros
@cindex pmacros

Preprocessor macros provide a way of simplifying the writing of
@file{.cpu} files and serve the same purpose that macros do in C.

@menu
* Defining a preprocessor macro:: @code{define-pmacro}
* Using preprocessor macros::
* Macro expansion::               The @code{pmacro-expand} procedure
* Default argument values::       Specifying default values of arguments
* Multiple output expressions::   Using @code{begin}
* Symbol concatenation::          The @code{.sym} builtin
* String concatenation::          The @code{.str} builtin
* Convert a number to a hex::     The @code{.hex} builtin
* Convert a string to uppercase:: The @code{.upcase} builtin
* Convert a string to lowercase:: The @code{.downcase} builtin
* Getting part of a string::      The @code{.substr} builtin
* List splicing::                 The @code{.splice} builtin
* Number generation::             The @code{.iota} builtin
* Mapping a macro over a list::   The @code{.map} builtin
* Applying a macro to a list::    The @code{.apply} builtin
* Defining a macro inline::       The @code{.pmacro} builtin
* Passing macros as arguments::   Passing a macro to another macro
@end menu

@node Defining a preprocessor macro
@section Defining a preprocessor macro
@cindex define-pmacro

Preprocessor macros are defined with:

@smallexample
(define-pmacro (name parm1 parm2 ... parmN)
  expansion
)
@end smallexample

The result is @samp{expansion} with parameters replaced with the actual
arguments of the macro invocation.  Free variables are left unchanged.
[A "free variable", as defined here, is one that doesn't appear in the
parameter list.]

@c ??? This used to be true, but currently isn't.
@c If the result is another macro invocation, it is expanded in turn.  

@samp{expansion} must be exactly one expression.

@node Using preprocessor macros
@section Using preprocessor macros

Preprocessor macros are invoked in either of two ways: positional arguments
and arguments by name.
@c Rather lame wording.

@smallexample
(define-pmacro (foo arg1 arg2) (bar arg1 arg2))

; Invoke by positional arguments.

(foo abc def) ==> (bar abc def)

; Invoke by naming arguments.

(foo #:arg1 ghi #:arg2 jkl) ==> (bar ghi jkl)
@end smallexample

@c If you think more should be said here, I agree.
@c Please think of something.

@node Macro expansion
@section Macro expansion

At the implementation level, pmacros are expand with the
@code{pmacro-expand} Scheme procedure.

The following is executed from a Guile shell, as opposed to 
appearing in a cpu description file, hence the extra quoting.

@smallexample
guile> (define-pmacro '(foo a b) '(+ a b))
guile> (pmacro-expand '(foo 3 4))
(+ 3 4)
@end smallexample

@node Default argument values
@section Default argument values

Invoking pmacros by specifying argument names allows some, or all,
arguments to be elided and thus allows for arguments to have default values.

Specify default values with the following syntax.

@smallexample
(define-pmacro (macro-name (arg1 . default-value)
                           (arg2 . default value) ...)
  ...
)
@end smallexample

Example:

@smallexample
(define-pmacro (foo (arg1 . 1) (arg2 . 2))
  (bar arg1 arg2)
)

(foo #:arg2 33) ==> (bar 1 33)
@end smallexample

@node Multiple output expressions
@section Multiple output expressions
@cindex begin

The result of a preprocessor macro is exactly one expression.
It is often useful, however, to return multiple expressions, say for
example when you want one macro to define several instructions.

The way to do this is to enclose all the expressions with @code{begin}.
@code{begin} is only valid at the top [definition] level.

??? It's moderately clumsy to restrict @code{begin} like this.
Using @code{sequence} for this purpose might be cleaner except that
sequence locals don't make sense in this context (though perhaps that's
a lesser evil).  In the end, @code{begin} can be shorthand for a void-mode
sequence with no locals so I haven't been in a rush to resolve this.

@node Symbol concatenation
@section Symbol concatenation
@cindex .sym

Symbol and string concatenation are supported. Symbol concatenation is
done with:

@code{(.sym arg1 arg2 ...)}

Acceptable arguments are symbols, strings, and numbers.
The result is a symbol with the arguments concatenated together.
Numbers are converted to a string, base 10, and then to a symbol.
The result must be a valid Scheme symbol with the additional restriction
that the first character must be a letter.

@node String concatenation
@section String concatenation
@cindex .str

String concatenation is done with

@code{(.str arg1 arg2 ...)}

Acceptable arguments are symbols, strings, and numbers.  The result is a
string with the arguments concatenated together.
Numbers are converted base 10.

Example:

@smallexample
(define-pmacro (bin-op mnemonic op2-op sem-op)
  (dni mnemonic
       (.str mnemonic " reg/reg")
       ()
       (.str mnemonic " $dr,$sr")
       (+ OP1_0 op2-op dr sr)
       (set dr (sem-op dr sr))
       ())
)
(bin-op and OP2_12 and)
(bin-op or OP2_14 or)
(bin-op xor OP2_13 xor)
@end smallexample

@node Convert a number to a hex
@section Convert a number to a hex
@cindex .hex

Convert a number to a lowercase hex string with @code{.hex}.  If
@code{width} is present, the result is that many characters beginning
with the least significant digit.  Zeros are prepended as necessary.

Syntax: @code{(.hex number [width])}

Examples:

@smallexample
(.hex 42)   --> "2a"
(.hex 42 1) --> "a"
(.hex 42 4) --> "002a"
@end smallexample

@node Convert a string to uppercase
@section Convert a string to uppercase
@cindex .upcase

Convert a string to uppercase with @code{.upcase}.

Syntax: @code{(.upcase string)}

Example:

@smallexample
(.upcase "foo!") --> "FOO!"
@end smallexample

@node Convert a string to lowercase
@section Convert a string to lowercase

Convert a string to lowercase with @code{.downcase}.

Syntax: @code{(.downcase string)}

Example:

@smallexample
(.downcase "BAR?") --> "bar?"
@end smallexample

@node Getting part of a string
@section Getting part of a string
@cindex .substr

Extract a part of a string with @code{.substr}.

Syntax: @code{(.substr string start end)}

where @samp{start} is the starting character, and @samp{end} is one past
the ending character.  Character numbering begins at position 0.
If @samp{start} and @samp{end} are the same, and both valid, the empty
string is returned.

Example:

@smallexample
(.substr "howzitgoineh?" 2 6) --> "wzit"
@end smallexample

@node List splicing
@section List splicing
@cindex .splice

It is often useful to splice a list into a "parent" list.
This is best explained with an example.

@smallexample
(define-pmacro (splice-test a b c)
               (.splice a (.unsplice b) c))
(pmacro-expand (splice-test (1 (2) 3)))

--> (1 2 3)
@end smallexample

Note that a level of parentheses around @code{2} has been removed.

This is useful, for example, when one wants to pass a list of fields to
a macro that defines an instruction.  For example:

@smallexample
(define-pmacro (cond-move-1 name comment mnemonic cc-prefix cc-name cc-opcode
			    src-name src-opcode cond test)
  (dni name
       (.str "move %" cc-name " " comment ", v9 page 191")
       ((MACH64))
       (.str mnemonic " " cc-prefix cc-name ",$" src-name ",$rd")
       (.splice + OP_2 rd OP3_MOVCC cond
		(.unsplice cc-opcode) (.unsplice src-opcode))
       (if (test cc-name)
	   (set rd src-name))
       ())
)
@end smallexample

This macro, taken from @file{sparc64.cpu}, defines a conditional move
instruction. Arguments @code{cc-opcode} and @code{src-opcode} are lists
of fields. The macro is invoked with (simplified from @file{sparc64.cpu}):

@smallexample
(cond-move-1 mova-icc "blah ..." mova
             "%" icc ((f-fmt4-cc2 1) (f-fmt4-cc1-0 0))
             rs2 ((f-i 0) (f-fmt4-res10-6 0) rs2)
             CC_A test-always)
(cond-move-1 mova-imm-icc "blah ..." mova
             "%" icc ((f-fmt4-cc2 1) (f-fmt4-cc1-0 0))
             simm11 ((f-i 1) simm11)
             CC_A test-always)
@end smallexample

Macro @code{cond-move-1} is being used here to define both the register
and the immediate value case.  Each case has a slightly different list
of opcode fields.  Without the use of @code{.splice}/@code{.unsplice},
the resulting formats would be:

@smallexample
(+ OP_2 rd OP3_MOVCC CC_A ((f-fmt4-cc2-1) (f-fmt4-cc1-0 0))
   ((f-i 0) (f-fmt4-res10-6 0) rs2))

and

(+ OP_2 rd OP3_MOVCC CC_A ((f-fmt4-cc2-1) (f-fmt4-cc1-0 0))
   ((f-i 1) simm11))
@end smallexample

respectively.  This is not what is wanted.  What is wanted is

@smallexample
(+ OP_2 rd OP3_MOVCC CC_A (f-fmt4-cc2-1) (f-fmt4-cc1-0 0)
   (f-i 0) (f-fmt4-res10-6 0) rs2)

and

(+ OP_2 rd OP3_MOVCC CC_A (f-fmt4-cc2-1) (f-fmt4-cc1-0 0)
   (f-i 1) simm11)
@end smallexample

respectively, which is what @code{.splice} achieves.

@code{.unsplice} is a special reserved symbol that is only recognized inside
@code{.splice}.

@node Number generation
@section Number generation
@cindex .iota
@cindex Number generation

Machine descriptions often require a list of sequential numbers.
Generate a list of numbers with the @code{.iota} builtin macro.

The syntax is @samp{(.iota count [start [incr]])}.

Examples:

@smallexample
(.iota 5)      --> 0 1 2 3 4
(.iota 5 4)    --> 4 5 6 7 8
(.iota 5 5 -1) --> 5 4 3 2 1
@end smallexample

@node Mapping a macro over a list
@section Mapping a macro over a list
@cindex .map

Apply a macro to each element of a list, or set of lists, with @code{.map}.

The syntax is @samp{(.map macro-name list1 [list2 ...])}.

The result is a list with @samp{macro-name} applied to each element of
@samp{listN}.  @samp{macro-name} should take as many arguments as there
are lists.  This is often useful in constructing enum and register name lists.

Example:

@smallexample
(define-pmacro (foo name number) ((.sym X name) number))
(.map foo (A B C D E) (.iota 5))

-->

((XA 0) (XB 1) (XC 2) (XD 3) (XE 4))
@end smallexample

@node Applying a macro to a list
@section Applying a macro to a list
@cindex .apply

Invoke a macro with each argument coming from an element of a list,
with @code{.apply}.

The syntax is @samp{(.apply macro-name list)}.

The result is the result of invoking macro @samp{macro-name}.
@samp{macro-name} should take as many arguments as there elements in
@samp{list}.  If @samp{macro-name} takes a variable number of trailing
arguments, there must be at least as many list elements as there are
fixed arguments.
@c clumsily worded or what

Example:
@c need a more useful example

@smallexample
(.apply .str (.iota 5))

-->

"01234"
@end smallexample

Note that @code{(.str (.iota 5))} is an error.  Here the list
@samp{(0 1 2 3 4)} is passed as the first argument of @code{.str},
which is wrong.

@node Defining a macro inline
@section Defining a macro inline
@cindex .pmacro

Define a macro inline with @code{.pmacro}.
This is only supported when passing macros as arguments to other macros.

@smallexample
(define-pmacro (load-op suffix op2-op mode ext-op)
  (begin
    (dni (.sym ld suffix) (.str "ld" suffix)
	 ()
	 (.str "ld" suffix " $dr,@@$sr")
	 (+ OP1_2 op2-op dr sr)
	 (set dr (ext-op WI (mem: mode sr)))
	 ())
  )
)

(load-op "" OP2_12 WI (.pmacro (mode expr) expr))
(load-op b OP2_8 QI (.pmacro (mode expr) (ext: mode expr)))
(load-op h OP2_10 HI (.pmacro (mode expr) (ext: mode expr)))
(load-op ub OP2_9 QI (.pmacro (mode expr) (zext: mode expr)))
(load-op uh OP2_11 HI (.pmacro (mode expr) (zext: mode expr)))
@end smallexample

Currently, .pmacro's don't bind the way Scheme lambda expressions do.
For example, arg2 in the second pmacro is not bound to the arg2 argument
of the first pmacro.

@smallexample
(define-pmacro (foo arg1 arg2) ((.pmacro (bar) (+ arg2 bar)) arg1))
(foo 3 4) ==> (+ arg2 3)
@end smallexample

One can make an argument either way.  I'm not sure what the right thing
to do here is (leave things as is, or have lexical binding like Scheme).

@node Passing macros as arguments
@section Passing macros as arguments

Macros may be passed to other macros.

Example:

@smallexample
(define-pmacro (no-ext-expr mode expr) expr)
(define-pmacro (ext-expr mode expr) (ext: mode expr))
(define-pmacro (zext-expr mode expr) (zext: mode expr))

(define-pmacro (load-op suffix op2-op mode ext-op)
  (begin
    (dni (.sym ld suffix) (.str "ld" suffix)
	 ()
	 (.str "ld" suffix " $dr,@@$sr")
	 (+ OP1_2 op2-op dr sr)
	 (set dr (ext-op WI (mem: mode sr)))
	 ())
  )
)

(load-op "" OP2_12 WI no-ext-expr)
(load-op b OP2_8 QI ext-expr)
(load-op h OP2_10 HI ext-expr)
(load-op ub OP2_9 QI zext-expr)
(load-op uh OP2_11 HI zext-expr)
@end smallexample
