opt: Make break and goto not fallthrough

As we can optimize dead code a bit already it's fitting
to disable code emission after break and goto.

tccgen.c

@@ -5396,7 +5396,8 @@ static void block(int *bsym, int *csym, int is_expr)
 	    nocode_wanted |= 2;
 	a = gvtst(1, 0);
         block(bsym, csym, 0);
-	nocode_wanted = saved_nocode_wanted;
+	if (cond != 1)
+	    nocode_wanted = saved_nocode_wanted;
         c = tok;
         if (c == TOK_ELSE) {
             next();
@@ -5406,10 +5407,12 @@ static void block(int *bsym, int *csym, int is_expr)
             gsym(a);
             block(bsym, csym, 0);
             gsym(d); /* patch else jmp */
-	    nocode_wanted = saved_nocode_wanted;
+	    if (cond != 0)
+		nocode_wanted = saved_nocode_wanted;
         } else
             gsym(a);
     } else if (tok == TOK_WHILE) {
+	int saved_nocode_wanted;
 	nocode_wanted &= ~2;
         next();
         d = ind;
@@ -5420,7 +5423,9 @@ static void block(int *bsym, int *csym, int is_expr)
         a = gvtst(1, 0);
         b = 0;
         ++local_scope;
+	saved_nocode_wanted = nocode_wanted;
         block(&a, &b, 0);
+	nocode_wanted = saved_nocode_wanted;
         --local_scope;
         if(!nocode_wanted)
             gjmp_addr(d);
@@ -5556,6 +5561,7 @@ static void block(int *bsym, int *csym, int is_expr)
         /* jump unless last stmt in top-level block */
         if (tok != '}' || local_scope != 1)
             rsym = gjmp(rsym);
+	nocode_wanted |= 2;
     } else if (tok == TOK_BREAK) {
         /* compute jump */
         if (!bsym)
@@ -5563,6 +5569,7 @@ static void block(int *bsym, int *csym, int is_expr)
         *bsym = gjmp(*bsym);
         next();
         skip(';');
+	nocode_wanted |= 2;
     } else if (tok == TOK_CONTINUE) {
         /* compute jump */
         if (!csym)
@@ -5573,6 +5580,7 @@ static void block(int *bsym, int *csym, int is_expr)
         skip(';');
     } else if (tok == TOK_FOR) {
         int e;
+	int saved_nocode_wanted;
 	nocode_wanted &= ~2;
         next();
         skip('(');
@@ -5607,7 +5615,9 @@ static void block(int *bsym, int *csym, int is_expr)
             gsym(e);
         }
         skip(')');
+	saved_nocode_wanted = nocode_wanted;
         block(&a, &b, 0);
+	nocode_wanted = saved_nocode_wanted;
         if(!nocode_wanted)
             gjmp_addr(c);
         gsym(a);
@@ -5617,13 +5627,16 @@ static void block(int *bsym, int *csym, int is_expr)
 
     } else 
     if (tok == TOK_DO) {
+	int saved_nocode_wanted;
 	nocode_wanted &= ~2;
         next();
         a = 0;
         b = 0;
         d = ind;
         vla_sp_restore();
+	saved_nocode_wanted = nocode_wanted;
         block(&a, &b, 0);
+	nocode_wanted = saved_nocode_wanted;
         skip(TOK_WHILE);
         skip('(');
         gsym(b);
@@ -5637,6 +5650,7 @@ static void block(int *bsym, int *csym, int is_expr)
     } else
     if (tok == TOK_SWITCH) {
         struct switch_t *saved, sw;
+	int saved_nocode_wanted = nocode_wanted;
         next();
         skip('(');
         gexpr();
@@ -5650,6 +5664,7 @@ static void block(int *bsym, int *csym, int is_expr)
         saved = cur_switch;
         cur_switch = &sw;
         block(&a, csym, 0);
+	nocode_wanted = saved_nocode_wanted;
         a = gjmp(a); /* add implicit break */
         /* case lookup */
         gsym(b);

tests/tcctest.c

@@ -1184,6 +1184,57 @@ void optimize_out(void)
     printf("oo:%d\n", defined_function());
   else
     printf("oo:%d\n", undefined_function());
+  while (1) {
+      printf("oow:%d\n", defined_function());
+      break;
+      printf("oow:%d\n", undefined_function());
+  }
+  j = 1;
+  /* Following is a switch without {} block intentionally.  */
+  switch (j)
+    case 1: break;
+  printf ("oos:%d\n", defined_function());
+  /* The following break shouldn't lead to disabled code after
+     the while.  */
+  while (1)
+    break;
+  printf ("ool1:%d\n", defined_function());
+  /* Same for the other types of loops.  */
+  do
+    break;
+  while (1);
+  printf ("ool2:%d\n", defined_function());
+  for (;;)
+    break;
+  printf ("ool3:%d\n", defined_function());
+  /* Normal {} blocks without controlling statements
+     shouldn't reactivate code emission */
+  while (1) {
+	{
+	  break;
+	}
+      printf ("ool4:%d\n", undefined_function());
+  }
+  j = 1;
+  while (j) {
+      if (j == 0)
+	break; /* this break shouldn't disable code outside the if. */
+      printf("ool5:%d\n", defined_function());
+      j--;
+  }
+
+  j = 1;
+  while (j) {
+      if (1)
+	j--;
+      else
+	breakhere: break;
+      printf("ool6:%d\n", defined_function());
+      goto breakhere;
+  }
+  if (1)
+    return;
+  printf ("oor:%d\n", undefined_function());
 }
 
 int defined_function(void)