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Add optimize function() to cc2

This function runs all the possible optimizations that can be applied.
At this moment only reduction of casting can be used.

--- a/cc2/Makefile

+++ b/cc2/Makefile

@@ -1,5 +1,5 @@

-OBJS = main.o parser.o cgen.o code.o

+OBJS = main.o parser.o cgen.o code.o optm.o

 CPPFLAGS = -I../inc

 LDFLAGS = -L../lib

--- a/cc2/cc2.h

+++ b/cc2/cc2.h

@@ -117,4 +117,5 @@

 extern void apply(Node *list[], Node *(*fun)(Node *));

 extern Symbol *parse(void);

 extern void code(char op, ...);

+extern Node *optimize(Node *np);

 extern void prtree(Node *np);

--- a/cc2/main.c

+++ b/cc2/main.c

@@ -31,6 +31,7 @@

 	Symbol *fun;

 	while (!feof(stdin) && (fun = parse())) {

+		apply(fun->u.f.body, optimize);

 		apply(fun->u.f.body, genaddable);

 		generate(fun);

 	}

--- /dev/null

+++ b/cc2/optm.c

@@ -1,0 +1,43 @@

+

+#include <stddef.h>

+#include <stdint.h>

+

+#include <cc.h>

+#include "cc2.h"

+

+

+#include <stdio.h>

+

+static Node *

+optcasts(Node *np, Type *tp)

+{

+	if (!np)

+		return NULL;

+

+repeat:

+	switch (np->op) {

+	case OCAST:

+		/* TODO: be careful with the sign */

+		if (np->type->c_int && np->type->size >= tp->size) {

+			np = np->left;

+			goto repeat;

+		}

+		break;

+	case OASSIG:

+		tp = np->type;

+		break;

+	default:

+		np->type = tp;

+	}

+

+	np->left = optcasts(np->left, tp);

+	np->right = optcasts(np->right, tp);

+	return np;			

+}

+

+Node *

+optimize(Node *np)

+{

+	np = optcasts(np, np->type);

+	return np;

+}