Append a new sblock for return when necessary.

If the final block ends in a conditional statement, appending return to the
block will hide the conditional statement from the flow analyzer. This may
cause the conditional statement's destination node be become unreachable
according to the analyzer and thus eliminated. The label for the branch
then loses its target sblock and thus the code generator will produce a
zero-distance jump resulting in an infinite loop.

Thus, if the final block ends in a conditional statement (or, for
completeness, a call statement), append a new empty block before adding the
return statement.

tools/qfcc/source/statements.c

@@ -1512,7 +1512,7 @@ remove_dead_blocks (sblock_t *blocks)
 static void
 check_final_block (sblock_t *sblock)
 {
-	statement_t *s;
+	statement_t *s = 0;
 	symbol_t   *return_symbol = 0;
 	def_t      *return_def = 0;
 	operand_t  *return_operand = 0;
@@ -1531,6 +1531,12 @@ check_final_block (sblock_t *sblock)
 	}
 	if (current_func->sym->type->t.func.type != &type_void)
 		warning (0, "control reaches end of non-void function");
+	if (s && s->type >= st_func) {
+		// func and flow end blocks, so we need to add a new block to take the
+		// return
+		sblock->next = new_sblock ();
+		sblock = sblock->next;
+	}
 	if (options.traditional || options.code.progsversion == PROG_ID_VERSION) {
 		return_symbol = make_symbol (".return", &type_param, pr.symtab->space,
 									 sc_extern);

tools/qfcc/test/Makefile.am

@@ -29,7 +29,8 @@ test_progs_dat=\
 	structlive.dat \
 	structptr.dat \
 	vecinit.dat \
-	while.dat
+	while.dat \
+	voidfor.dat
 
 fail_progs_dat=\
 	$E
@@ -120,6 +121,13 @@ while.dat: $(while_obj) $(QFCC_DEP)
 while.run: Makefile build-run
 	$(srcdir)/build-run $@
 
+voidfor_dat_SOURCES=voidfor.r
+voidfor_obj=$(voidfor_dat_SOURCES:.r=.qfo)
+voidfor.dat: $(voidfor_obj) $(QFCC_DEP)
+	$(QFCC) $(QCFLAGS) -o $@ $(voidfor_obj)
+voidfor.run: Makefile build-run
+	$(srcdir)/build-run $@
+
 include ./$(DEPDIR)/*.Qo
 
 EXTRA_DIST= test-bi.h build-run

tools/qfcc/test/voidfor.r

@@ -0,0 +1,17 @@
+void bar ()
+{
+}
+
+void foo ()
+{
+	int i;
+
+	for (i = 0; i < 11; i++)
+		bar ();
+}
+
+int main ()
+{
+	foo ();
+	return 0;
+}