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Fix push() in cgen

Push() was marking as pushed the static node that is used for
registers, but it was not the node that was pushed. There were
another problems, mainly related to pair register, because
each element can represent different nodes.

--- a/cc2/cgen.c

+++ b/cc2/cgen.c

@@ -11,6 +11,13 @@

 static Node *reguse[NREGS];

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

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

+static char pair[] = {

+	[A] = A,

+	[H] = HL, [L] = HL,

+	[B] = BC, [C] = BC,

+	[D] = DE, [E] = DE,

+	[IYL] = IY, [IYH] = IY

+};

 Node

 reg_E = {

@@ -162,10 +169,17 @@

 }

 static void

-push(Node *np)

+push(uint8_t reg)

 {

-	code(PUSH, NULL, np);

-	np->op = PUSHED;

+	Node *np;

+

+	if (reg < NREGS)

+		reg = pair[reg];

+	if ((np = reguse[lower[reg]]) != NULL)

+		np->op = PUSHED;

+	if ((np = reguse[upper[reg]]) != NULL)

+		np->op = PUSHED;

+	code(PUSH, NULL, regs[reg]);

 }

 static void

@@ -174,12 +188,12 @@

 	switch (np->type.size) {

 	case 1:

 		if (reguse[A])

-			push(reguse[A]);

+			push(A);

 		moveto(np, A);

 		break;

 	case 2:

 		if (reguse[H] || reguse[L])

-			push(&reg_HL);

+			push(HL);

 		moveto(np, HL);

 		break;

 	case 4:

@@ -192,7 +206,7 @@

 index(Node *np)

 {

 	if (reguse[H] || reguse[L])

-		push(&reg_HL);

+		push(HL);

 	code(LDI, &reg_HL, np);

 	reguse[H] = reguse[L] = np;

 	np->op = INDEX;