Author: kjs
Date: Sun Aug 24 04:43:39 2008
New Revision: 30507
Modified:
trunk/compilers/pirc/new/pir.y
Log:
[pirc/new] add documentation to pir.y
+ add function documentation
+ add some comments here and there
+ add doc. about impl of constant folding and instr. select.
Modified: trunk/compilers/pirc/new/pir.y
==============================================================================
--- trunk/compilers/pirc/new/pir.y (original)
+++ trunk/compilers/pirc/new/pir.y Sun Aug 24 04:43:39 2008
@@ -163,7 +163,7 @@
#endif
-
+/* the parser aborts if there are more than 10 errors */
#define MAX_NUM_ERRORS 10
@@ -455,9 +455,6 @@
{ set_hll_map($2, $4); }
;
-
-/* Namespaces */
-
namespace_decl : ".namespace" '[' opt_namespace ']'
{ set_namespace(lexer, $3); }
;
@@ -478,9 +475,6 @@
{ $$ = expr_from_const(new_const(STRING_TYPE,
$1)); }
;
-
-/* Sub definition */
-
sub_def : sub_head sub_flags "\n"
parameters
instructions
@@ -565,6 +559,7 @@
| instructions instruction
;
+/* helper rule to create a new instruction node before the instruction is
parsed */
instruction : { new_instr(lexer); }
instr
;
@@ -644,10 +639,10 @@
keyaccess : target keylist
{
- if ($1->type != PMC_TYPE)
- yyerror(yyscanner, lexer, "indexed object is
not of type PMC");
- else
+ if ($1->type == PMC_TYPE) /* only PMCs can be
indexed */
set_target_key($1, $2);
+ else
+ yyerror(yyscanner, lexer, "indexed object is not
of type PMC");
$$ = $1;
}
@@ -667,6 +662,47 @@
assignment_stat : assignment "\n"
;
+/*
+
+=head2 Constant folding and Instruction Selection
+
+Constant folding is implemented in the parser. This is done by writing
+many specific alternatives, instead of using C<general> rules that
+would match all input. This way, the parser's matching mechanism is
+used to select specific cases, for instance adding 2 integer numbers.
+
+Based on the values of the terminals, some instructions can be optimized
+by selecting more efficient equivalent instructions.
+
+The table below specifies how this is done. Terminals are numbered and
+referenced using YACC syntax ($1 for the first terminal, $2 for the
+second, etc.).
+
+
+ rule | instruction | condition
+
=================================================================================
+ target '=' {integer, number} | set $1, $3 | $3 != 0
+ | null $1 | $3 == 0
+ | |
+ target '=' target | set $1, $3 | $1 != $3
+ | noop | $1 == $3
+ | |
+ target '=' target binop {integer, | $4 $1, $3, $5 | $1 != $3
+ number} | inc/dec $1 | $1 == $3, $5
== 1, $4 == {'+', '-'}
+ | noop | $1 == $3, $5
== 0, $4 == {'+', '-'}
+ | null $1 | $1 == $3, $5
== 0, $4 == {'*'}
+ | error: divide by 0 | $1 == $3, $5
== 0, $4 == {'/', '//'}
+ | $4 $1, $5 | $1 == $3, $5
!= {0, 1}
+ | |
+ target '=' target binop {string, | $4 $1, $5 | $1 == $3
+ target} | $4 $1, $3, $5 | $1 != $3
+ | |
+
+
+=cut
+
+*/
+
assignment : set_instruction
| target '=' TK_INTC
{
@@ -819,7 +855,7 @@
{ set_instrf(lexer, "set", "%C", fold_n_i(yyscanner,
$1, $2, $3)); }
;
-
+/* all variants of the "set" opcode */
set_instruction : "set" target ',' keyaccess
{ set_instrf(lexer, "set", "%T%T", $2, $4); }
| "set" keyaccess ',' expression
@@ -1210,9 +1246,9 @@
local_var_name : identifier
{ $$ = $1; }
| TK_SYMBOL
- {
+ { /* if a symbol was found, that means it was already
declared */
yyerror(yyscanner, lexer, "local symbol already
declared!");
- $$ = $1->name;
+ $$ = $1->name; /* always return something to prevent
seg. faults. */
}
;
@@ -1222,7 +1258,7 @@
lex_decl : ".lex" TK_STRINGC ',' target "\n"
{
- if ($4->type == PMC_TYPE)
+ if ($4->type == PMC_TYPE) /* only PMCs can be stored
as lexicals */
set_lex_flag($4, $2);
else
yyerror(yyscanner, lexer,
@@ -1686,7 +1722,7 @@
/*
-=head1 Constant folding routines.
+=head1 FUNCTIONS
=over 4
@@ -2092,16 +2128,49 @@
return NULL;
}
+/*
+
+=item C<static int
+evaluate_i_i(int a, pir_rel_operator op, double b)>
+
+Compare C<a> with C<b> according to the relational operator C<op>.
+Wrapper for C<evaluate_n_n>, which takes arguments of type double.
+
+=cut
+
+*/
static int
evaluate_i_i(int a, pir_rel_operator op, int b) {
return evaluate_n_n(a, op, b);
}
+/*
+
+=item C<static int
+evaluate_n_i(int a, pir_rel_operator op, double b)>
+
+Compare C<a> with C<b> according to the relational operator C<op>.
+Wrapper for C<evaluate_n_n>, which takes arguments of type double.
+
+=cut
+
+*/
static int
evaluate_n_i(double a, pir_rel_operator op, int b) {
return evaluate_n_n(a, op, b);
}
+/*
+
+=item C<static int
+evaluate_i_n(int a, pir_rel_operator op, double b)>
+
+Compare C<a> with C<b> according to the relational operator C<op>.
+Wrapper for C<evaluate_n_n>, which takes arguments of type double.
+
+=cut
+
+*/
static int
evaluate_i_n(int a, pir_rel_operator op, double b) {
return evaluate_n_n(a, op, b);
@@ -2138,6 +2207,19 @@
}
}
+/*
+
+=item C<static int
+evaluate_s_s(char *a, pir_rel_operator op, char *b)>
+
+Compare string C<a> with string C<b> using the operator C<op>.
+The function uses C's C<strcmp> function. Based on that result,
+which can be -1 (smaller), 0 (equal) or 1 (larger), a boolean
+result is returned.
+
+=cut
+
+*/
static int
evaluate_s_s(char *a, pir_rel_operator op, char *b) {
int result = strcmp(a, b);
