re PR target/80993 ([msp430] __attribute__((interrupt)) should imply __attribute__((used)))

	PR target/80993
	* gcc/config/msp430/msp430.c (msp430_attr): Mark interrupt
	handlers as used.

From-SVN: r251410

gcc/ChangeLog

+2017-08-29  Jozef Lawrynowicz  <jozef.l@somniumtech.com>
+
+	PR target/80993
+	* gcc/config/msp430/msp430.c (msp430_attr): Mark interrupt
+	handlers as used.
+
 2017-08-29  Richard Biener  <rguenther@suse.de>
 
 	* dwarf2out.c (add_dwarf_attr): When checking is enabled verify

gcc/config/msp430/msp430.c

@@ -1904,6 +1904,10 @@ msp430_attr (tree * node,
 
       if (! TREE_PUBLIC (* node))
 	message = "interrupt handlers cannot be static";
+
+      /* Ensure interrupt handlers never get optimised out.  */
+      TREE_USED (* node) = 1;
+      DECL_PRESERVE_P (* node) = 1;
     }
   else if (TREE_NAME_EQ (name, ATTR_REENT))
     {

gcc/testsuite/gcc.target/msp430/pr80993.c

+/* { dg-do link } */
+/* { dg-options "--save-temps -msim -flto -Os" } */
+/* { dg-final { scan-file "pr80993.exe.ltrans0.s" no_ref_handler } } */
+
+void __attribute__((interrupt)) no_ref_handler (void)
+{
+  while (1);
+}
+
+int main (void)
+{
+  return 0;
+}