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[cc2-qbe] Add return statements to qbe

We need return statements because qne doesn't support orphan labels
at the end of functions, so we have to add return statements in these
cases.

--- a/cc2/arch/qbe/arch.h

+++ b/cc2/arch/qbe/arch.h

@@ -130,5 +130,6 @@

 	ASEXTS,

 	ASTRUNCD,

-	ASJMP

+	ASJMP,

+	ASRET,

 };

--- a/cc2/arch/qbe/cgen.c

+++ b/cc2/arch/qbe/cgen.c

@@ -225,7 +225,15 @@

 	if (!np)

 		return NULL;

-	setlabel(np->label);

+	if (np->label) {

+		setlabel(np->label);

+		if (np->next == NULL) {

+			Node *tmp = newnode();

+			tmp->op = ORET;

+			addstmt(tmp);

+			prevstmt();

+		}

+	}

 	l = cgen(np->left);

 	r = cgen(np->right);

 	tp = &np->type;

@@ -333,6 +341,10 @@

 		code(ASJMP, np, NULL, NULL);

 		return NULL;

 	case ORET:

+		if (l && (l->flags & (ISTMP|ISCONS)) == 0)

+			l = np->left = load(l);

+		code(ASRET, l, NULL, NULL);

+		return NULL;

 	case OCASE:

 	case ODEFAULT:

 	case OTABLE:

--- a/cc2/arch/qbe/code.c

+++ b/cc2/arch/qbe/code.c

@@ -9,7 +9,7 @@

 #define ADDR_LEN (IDENTSIZ+64)

-static void binary(void), unary(void), store(void), jmp(void);

+static void binary(void), unary(void), store(void), jmp(void), ret(void);

 static struct opdata {

 	void (*fun)(void);

@@ -123,6 +123,7 @@

 	[ASSLTOS]= {.fun = unary, .txt = "truncd", .letter = 's'},

 	[ASJMP]  = {.fun = jmp},

+	[ASRET]  = {.fun = ret},

 };

 static char buff[ADDR_LEN];

@@ -388,6 +389,15 @@

 	strcpy(to, addr2txt(&pc->to));

 	strcpy(from, addr2txt(&pc->from1));

 	printf("\t%s %c=\t%s\t%s\n", to, p->letter, p->txt, from);

+}

+

+static void

+ret(void)

+{

+	if (pc->from1.kind == SNONE)

+		puts("\t\tret");

+	else

+		printf("\t\tret\t%s\n", addr2txt(&pc->from1));

 }

 static void

--- a/cc2/cc2.h

+++ b/cc2/cc2.h

@@ -210,6 +210,8 @@

 extern void deltree(Node *np);

 extern Node *newnode(void);

 extern Node *addstmt(Node *np);

+extern Node *prevstmt(void), *nextstmt(void);

+

 /* symbol.c */

 #define TMPSYM  0

--- a/cc2/node.c

+++ b/cc2/node.c

@@ -83,6 +83,12 @@

 	return curstmt = curstmt->next;

 }

+Node *

+prevstmt(void)

+{

+	return curstmt = curstmt->prev;

+}

+

 void

 delnode(Node *np)

 {