c-family: Implicitly return zero from main even on freestanding

... unless marked noreturn.

This should not get in anyone's way, but should permit the use of main()
in freestanding more easily, especially for writing test cases that
should work both in freestanding and hosted modes.

gcc/c/ChangeLog:

	* c-decl.cc (finish_function): Ignore hosted when deciding
	whether to implicitly return zero, but check noreturn.
	* c-objc-common.cc (c_missing_noreturn_ok_p): Loosen the
	requirements to just MAIN_NAME_P when hosted, or `int main'
	otherwise.

gcc/cp/ChangeLog:

	* cp-tree.h (DECL_MAIN_P): Move most logic, besides the hosted
	check, from here...
	(DECL_MAIN_ANY_P): ... to here, so that it can be reused ...
	(DECL_MAIN_FREESTANDING_P): ... here, with an additional
	constraint on (hosted OR return type == int)
	* decl.cc (finish_function): Use DECL_MAIN_FREESTANDING_P
	instead of DECL_MAIN_P, to loosen the hosted requirement, but
	check noreturn, before adding implicit returns.

gcc/testsuite/ChangeLog:

	* gcc.dg/noreturn-4.c: Removed.
	* g++.dg/freestanding-main.C: New test.
	* g++.dg/freestanding-nonint-main.C: New test.
	* gcc.dg/freestanding-main.c: New test.
	* gcc.dg/freestanding-nonint-main.c: New test.

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 80f6e91..4746e31 100644 (file)
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -10542,7 +10542,7 @@ finish_function (location_t end_loc)
   if (DECL_RESULT (fndecl) && DECL_RESULT (fndecl) != error_mark_node)
     DECL_CONTEXT (DECL_RESULT (fndecl)) = fndecl;
 
-  if (MAIN_NAME_P (DECL_NAME (fndecl)) && flag_hosted
+  if (MAIN_NAME_P (DECL_NAME (fndecl)) && !TREE_THIS_VOLATILE (fndecl)
       && TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (fndecl)))
       == integer_type_node && flag_isoc99)
     {

diff --git a/gcc/c/c-objc-common.cc b/gcc/c/c-objc-common.cc
index 70e10a9..b468091 100644 (file)
--- a/gcc/c/c-objc-common.cc
+++ b/gcc/c/c-objc-common.cc
@@ -37,9 +37,12 @@ static bool c_tree_printer (pretty_printer *, text_info *, const char *,
 bool
 c_missing_noreturn_ok_p (tree decl)
 {
-  /* A missing noreturn is not ok for freestanding implementations and
-     ok for the `main' function in hosted implementations.  */
-  return flag_hosted && MAIN_NAME_P (DECL_ASSEMBLER_NAME (decl));
+  /* A missing noreturn is ok for the `main' function.  */
+  if (!MAIN_NAME_P (DECL_ASSEMBLER_NAME (decl)))
+    return false;
+
+  return flag_hosted
+    || TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (decl))) == integer_type_node;
 }
 
 /* Called from check_global_declaration.  */

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 60a2510..2cca20b 100644 (file)
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -772,11 +772,20 @@ typedef struct ptrmem_cst * ptrmem_cst_t;
 
 /* Returns nonzero iff NODE is a declaration for the global function
    `main'.  */
-#define DECL_MAIN_P(NODE)                              \
+#define DECL_MAIN_ANY_P(NODE)                          \
    (DECL_EXTERN_C_FUNCTION_P (NODE)                    \
     && DECL_NAME (NODE) != NULL_TREE                   \
-    && MAIN_NAME_P (DECL_NAME (NODE))                  \
-    && flag_hosted)
+    && MAIN_NAME_P (DECL_NAME (NODE)))
+
+/* Nonzero iff NODE is a declaration for `int main', or we are hosted. */
+#define DECL_MAIN_FREESTANDING_P(NODE)                         \
+  (DECL_MAIN_ANY_P(NODE)                                       \
+   && (flag_hosted                                             \
+       || TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (NODE)))     \
+         == integer_type_node))
+
+/* Nonzero iff NODE is a declaration for `main', and we are hosted. */
+#define DECL_MAIN_P(NODE) (DECL_MAIN_ANY_P(NODE) && flag_hosted)
 
 /* Lookup walker marking.  */
 #define LOOKUP_SEEN_P(NODE) TREE_VISITED (NODE)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 85b892c..bc085f8 100644 (file)
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -17852,7 +17852,8 @@ finish_function (bool inline_p)
   if (!DECL_CLONED_FUNCTION_P (fndecl))
     {
       /* Make it so that `main' always returns 0 by default.  */
-      if (DECL_MAIN_P (current_function_decl))
+      if (DECL_MAIN_FREESTANDING_P (current_function_decl)
+         && !TREE_THIS_VOLATILE (current_function_decl))
        finish_return_stmt (integer_zero_node);
 
       if (use_eh_spec_block (current_function_decl))

diff --git a/gcc/testsuite/g++.dg/freestanding-main.C b/gcc/testsuite/g++.dg/freestanding-main.C
new file mode 100644 (file)
index 0000000..3718cc4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/freestanding-main.C
@@ -0,0 +1,5 @@
+/* Make sure we don't get a missing return warning on freestanding. */
+/* { dg-do compile } */
+/* { dg-options "-ffreestanding -Wreturn-type" } */
+
+int main() {}

diff --git a/gcc/testsuite/g++.dg/freestanding-nonint-main.C b/gcc/testsuite/g++.dg/freestanding-nonint-main.C
new file mode 100644 (file)
index 0000000..a8571cc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/freestanding-nonint-main.C
@@ -0,0 +1,5 @@
+/* Check that we get the right warning for nonint main in freestanding. */
+/* { dg-do compile } */
+/* { dg-options "-ffreestanding -Wreturn-type" } */
+
+const char *main() {} /* { dg-warning "-Wreturn-type" } */

diff --git a/gcc/testsuite/gcc.dg/freestanding-main.c b/gcc/testsuite/gcc.dg/freestanding-main.c
new file mode 100644 (file)
index 0000000..3718cc4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/freestanding-main.c
@@ -0,0 +1,5 @@
+/* Make sure we don't get a missing return warning on freestanding. */
+/* { dg-do compile } */
+/* { dg-options "-ffreestanding -Wreturn-type" } */
+
+int main() {}

diff --git a/gcc/testsuite/gcc.dg/freestanding-nonint-main.c b/gcc/testsuite/gcc.dg/freestanding-nonint-main.c
new file mode 100644 (file)
index 0000000..d839334
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/freestanding-nonint-main.c
@@ -0,0 +1,5 @@
+/* Check that we get the right warning for nonint main in freestanding. */
+/* { dg-do compile } */
+/* { dg-options "-ffreestanding -Wreturn-type" } */
+
+const char *main(void) {} /* { dg-warning "-Wreturn-type" } */

diff --git a/gcc/testsuite/gcc.dg/noreturn-4.c b/gcc/testsuite/gcc.dg/noreturn-4.c
deleted file mode 100644 (file)
index 6fe1447..0000000
--- a/gcc/testsuite/gcc.dg/noreturn-4.c
+++ /dev/null
@@ -1,10 +0,0 @@
-/* Check for "noreturn" warning in main. */
-/* { dg-do compile } */
-/* { dg-options "-O2 -Wmissing-noreturn -ffreestanding" } */
-extern void exit (int) __attribute__ ((__noreturn__));
-
-int
-main (void) /* { dg-warning "function might be candidate for attribute 'noreturn'" "warn for main" } */
-{
-  exit (0);
-}