Issue 6423 - Garbage is returned from void main()

src/statement.c

@@ -3538,7 +3538,6 @@ ReturnStatement::ReturnStatement(Loc loc, Expression *exp)
     : Statement(loc)
 {
     this->exp = exp;
-    this->implicit0 = 0;
 }
 
 Statement *ReturnStatement::syntaxCopy()
@@ -3570,13 +3569,6 @@ Statement *ReturnStatement::semantic(Scope *sc)
     if (tret)
         tbret = tret->toBasetype();
 
-    // main() returns 0, even if it returns void
-    if (!exp && (!tbret || tbret->ty == Tvoid) && fd->isMain())
-    {
-        implicit0 = 1;
-        exp = new IntegerExp(0);
-    }
-
     if (sc->flags & SCOPEcontract)
         error("return statements cannot be in contracts");
     if (sc->os && sc->os->tok != TOKon_scope_failure)
@@ -3760,7 +3752,7 @@ Statement *ReturnStatement::semantic(Scope *sc)
     {
         Statement *s;
 
-        if (exp && !implicit0)
+        if (exp)
         {
             exp = exp->implicitCastTo(sc, tret);
         }
@@ -3891,24 +3883,32 @@ Statement *ReturnStatement::semantic(Scope *sc)
         return gs;
     }
 
-    if (exp && tbret->ty == Tvoid && !implicit0)
+    if (tbret->ty == Tvoid)
     {
-        if (exp->type->ty != Tvoid)
+        if (exp && exp->type->ty != Tvoid)
         {
             error("cannot return non-void from void function");
         }
 
-        /* Replace:
-         *      return exp;
-         * with:
-         *      cast(void)exp; return;
-         */
-        Expression *ce = new CastExp(loc, exp, Type::tvoid);
-        Statement *s = new ExpStatement(loc, ce);
-        s = s->semantic(sc);
+        Expression *eret = exp;
+        // main() returns 0, even if it returns void
+        if (fd->isMain())
+            exp = new IntegerExp(0);
+        else
+            exp = NULL;
 
-        exp = NULL;
-        return new CompoundStatement(loc, s, this);
+        if (eret)
+        {
+            /* Replace:
+             *      return exp;
+             * with:
+             *      cast(void)exp; return;
+             */
+            Expression *ce = new CastExp(loc, eret, Type::tvoid);
+            Statement *s = new ExpStatement(loc, ce);
+            s = s->semantic(sc);
+            return new CompoundStatement(loc, s, this);
+        }
     }
 
     return this;

src/statement.h

@@ -522,7 +522,6 @@ class ReturnStatement : public Statement
 {
 public:
     Expression *exp;
-    bool implicit0;             // this is an implicit "return 0;"
 
     ReturnStatement(Loc loc, Expression *exp);
     Statement *syntaxCopy();

test/Makefile

@@ -134,6 +134,12 @@ DISABLED_TESTS += testargtypes
 DISABLED_TESTS += testxmm
 endif
 
+ifeq ($(OS),osx)
+ifeq ($(MODEL),64)
+DISABLED_TESTS += test6423
+endif
+endif
+
 runnable_tests=$(wildcard runnable/*.d) $(wildcard runnable/*.sh)
 runnable_test_results=$(addsuffix .out,$(addprefix $(RESULTS_DIR)/,$(runnable_tests)))
 

test/runnable/test6423.d

@@ -0,0 +1,24 @@
+
+bool flag;
+
+void f()
+{
+}
+
+void main()
+{
+    if (!flag)
+    {
+        flag = true;
+        caller();
+    }
+    return f();
+}
+
+alias maintype = extern(C) int function();
+
+void caller()
+{
+    auto fp = cast(maintype)&main;
+    assert(fp() == 0);
+}