C++ PATCH: PR 21228

[Mark Mitchell <mark at codesourcery dot com>]

This patch fixes PR 21228, a bogus warning with -Wunreachable-code.
The C++ front end was creating an EH_SPEC_BLOCK in implicitly defined
methods, but since the exception-specification for such a function is
the union of the specifications for all of the functions it calls,
the exception-specification will never be violated, and the middle
end warns about that fact.  Fixed by causing the front-end not to
generate the EH_SPEC_BLOCK for such functions.  (We still set
TYPE_RAISES_EXCEPTION on the function type for such functions, of
course.)

Tested on x86_64-unknown-linux-gnu, applied on the 4.0 branch, 4.1
branch, and (in a few minutes) the mainline.

--
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com

2005-12-20  Mark Mitchell  <mark@codesourcery.com>

	PR c++/21228
	* decl.c (use_eh_spec_block): New function.
	(store_parm_decls): Use it.
	(finish_function): Likewise.
	
2005-12-20  Mark Mitchell  <mark@codesourcery.com>

	PR c++/21228
	* g++.dg/warn/Wunreachable-code-2.C: New test.

Index: gcc/cp/decl.c
===================================================================
--- gcc/cp/decl.c	(revision 108836)
+++ gcc/cp/decl.c	(working copy)
@@ -10482,6 +10482,26 @@ start_function (cp_decl_specifier_seq *d
   return 1;
 }
 
+/* Returns true iff an EH_SPEC_BLOCK should be created in the body of
+   FN.  */
+
+static bool
+use_eh_spec_block (tree fn)
+{
+  return (flag_exceptions && flag_enforce_eh_specs
+	  && !processing_template_decl
+	  && TYPE_RAISES_EXCEPTIONS (TREE_TYPE (fn))
+	  /* Implicitly-generated constructors and destructors have
+	     exception specifications.  However, those specifications
+	     are the union of the possible exceptions specified by the
+	     constructors/destructors for bases and members, so no
+	     unallowed exception will ever reach this function.  By
+	     not creating the EH_SPEC_BLOCK we save a little memory,
+	     and we avoid spurious warnings about unreachable
+	     code.  */
+	  && !DECL_ARTIFICIAL (fn));
+}
+
 /* Store the parameter declarations into the current function declaration.
    This is called after parsing the parameter declarations, before
    digesting the body of the function.
@@ -10552,16 +10572,8 @@ store_parm_decls (tree current_function_
      DECL_ARGUMENTS is not modified.  */
   current_binding_level->names = chainon (nonparms, DECL_ARGUMENTS (fndecl));
 
-  /* For a cloned function, we've already got all the code we need;
-     there's no need to add any extra bits.  */
-  if (!DECL_CLONED_FUNCTION_P (fndecl))
-    {
-      /* Do the starting of the exception specifications, if we have any.  */
-      if (flag_exceptions && !processing_template_decl
-	  && flag_enforce_eh_specs
-	  && TYPE_RAISES_EXCEPTIONS (TREE_TYPE (current_function_decl)))
-	current_eh_spec_block = begin_eh_spec_block ();
-    }
+  if (use_eh_spec_block (current_function_decl))
+    current_eh_spec_block = begin_eh_spec_block ();
 }
 
 
@@ -10848,10 +10860,7 @@ finish_function (int flags)
 #endif
 	}
 
-      /* Finish dealing with exception specifiers.  */
-      if (flag_exceptions && !processing_template_decl
-	  && flag_enforce_eh_specs
-	  && TYPE_RAISES_EXCEPTIONS (TREE_TYPE (current_function_decl)))
+      if (use_eh_spec_block (current_function_decl))
 	finish_eh_spec_block (TYPE_RAISES_EXCEPTIONS
 			      (TREE_TYPE (current_function_decl)),
 			      current_eh_spec_block);
Index: gcc/testsuite/g++.dg/warn/Wunreachable-code-2.C
===================================================================
--- gcc/testsuite/g++.dg/warn/Wunreachable-code-2.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/Wunreachable-code-2.C	(revision 0)
@@ -0,0 +1,23 @@
+// PR c++/21228
+/* { dg-options "-Wunreachable-code" } */
+
+class testStringBase
+{
+public:
+  char *stringPtr;
+};
+
+class testString : public testStringBase
+{
+public:
+  testString();
+};
+
+testString::testString()
+{
+  stringPtr = (char *) 9;
+}
+ 
+int main(int argc, char **argv) {
+  testString s;
+}