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Add peephole infrastructure

The peephole will be necessary in some moment, so it is a good
idea to build it now. This small demo of peephole also allow
to simplify add(), and make it more suitable for other operations,
so maybe the code will be much clearer due to this change.

--- a/cc2/Makefile

+++ b/cc2/Makefile

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

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

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

 LIBS = -lcc

--- a/cc2/cc2.h

+++ b/cc2/cc2.h

@@ -157,8 +157,13 @@

 /* code.c */

 extern void code(uint8_t op, Node *to, Node *from);

+extern void inscode(uint8_t op, Addr *to, Addr *from);

 extern void writeout(void);

+extern void delcode(void);

 /* optm.c */

 extern void optimize(void);

 extern Node *imm(TINT i);

+

+/* peep.c */

+extern void peephole(void);

--- a/cc2/cgen.c

+++ b/cc2/cgen.c

@@ -7,7 +7,7 @@

 #include "cc2.h"

-static Node *reguse[NREGS];

+static Node *reguse[NPAIRS];

 static uint8_t upper[] = {[DE] = D, [HL] = H, [BC] = B,  [IY] = IYH};

 static uint8_t lower[] = {[DE] = E, [HL] = L, [BC] = C, [IY] = IYL};

 static uint8_t pair[] = {

@@ -301,17 +301,7 @@

 			abort();

 		}

 	add_A:

-		if (rp->op == CONST) {

-			if  ((i = rp->sym->u.imm) == 0)

-				goto update_A;

-			 if (i < 4) {

-				while (i--)

-					code(INC, lp, NULL);

-				goto update_A;

-			}

-		}

 		code(ADD, lp, rp);

-	update_A:

 		np->op = REG;

 		np->reg = A;

 		break;

--- a/cc2/code.c

+++ b/cc2/code.c

@@ -50,24 +50,25 @@

 Inst *pc, *prog;

-Inst *

+static void

 nextpc(void)

 {

 	Inst *new;

 	new = xmalloc(sizeof(*new));

-	new->prev = pc;

-	if (!pc)

+	if (!pc) {

+		new->next = NULL;

 		prog = new;

-	else

+	} else {

+		new->next = pc->next;

 		pc->next = new;

+	}

+

+	new->prev = pc;

+	new->to.kind = NONE;

+	new->from.kind = NONE;

 	pc = new;

-	pc->op = NOP;

-	pc->to.kind = NONE;

-	pc->from.kind = NONE;

-	pc->next = NULL;

-	return pc;

 }

 void

@@ -96,14 +97,41 @@

 void

 code(uint8_t op, Node *to, Node *from)

 {

-	Inst *ip;

-	ip = nextpc();

+	nextpc();

 	if (from)

-		addr(op, from, &ip->from);

+		addr(op, from, &pc->from);

 	if (to)

-		addr(op, to, &ip->to);

-	ip->op = op;

+		addr(op, to, &pc->to);

+	pc->op = op;

+}

+

+void

+inscode(uint8_t op, Addr *to, Addr *from)

+{

+	nextpc();

+	if (from)

+		pc->from = *from;

+	if (to)

+		pc->to = *to;

+	pc->op = op;

+}

+

+void

+delcode(void)

+{

+	Inst *prev = pc->prev, *next = pc->next;

+

+	free(pc);

+	if (!prev) {

+		pc = next;

+		prog = NULL;

+	} else {

+		pc = prev;

+		prev->next = next;

+		if (next)

+			next->prev = prev;

+	}

 }

 void

--- a/cc2/main.c

+++ b/cc2/main.c

@@ -47,6 +47,7 @@

 		optimize();

 		addable();

 		generate();

+		peephole();

 		writeout();

 	}

 	return 0;

--- /dev/null

+++ b/cc2/peep.c

@@ -1,0 +1,32 @@

+

+#include <inttypes.h>

+#include <stddef.h>

+

+#include "../inc/cc.h"

+#include "cc2.h"

+

+void

+peephole(void)

+{

+	Addr to, from;

+	TINT i;

+

+	for (pc = prog; pc; pc = pc->next) {

+		to = pc->to;

+		from = pc->from;

+

+		switch (pc->op) {

+		case ADD:

+			if (from.kind == CONST) {

+				if ((i = from.u.i) == 0 || i < 4) {

+					delcode();

+

+					while (i--)

+						inscode(INC, &to, NULL);

+				}

+			/* TODO: More optimizations (ex: -1) */

+			}

+			break;

+		}

+	}

+}