[google] Do not execute pass_warn_function_return after a syntax error (issue4629076)

Index: gcc/testsuite/g++.old-deja/g++.jason/report.C
===================================================================
--- gcc/testsuite/g++.old-deja/g++.jason/report.C	(revision 175523)
+++ gcc/testsuite/g++.old-deja/g++.jason/report.C	(working copy)
@@ -72,6 +72,3 @@  int darg (char X::*p)
 {
    undef3 (1); // { dg-error "" } implicit declaration
 }				// { dg-warning "no return statement" }
-
-// { dg-message "warning: control reaches end of non-void function" "" { target *-*-* } 36 }
-// { dg-message "warning: control reaches end of non-void function" "" { target *-*-* } 65 }
Index: gcc/testsuite/g++.dg/parse/cascading-errors.C
===================================================================
--- gcc/testsuite/g++.dg/parse/cascading-errors.C	(revision 0)
+++ gcc/testsuite/g++.dg/parse/cascading-errors.C	(revision 0)
@@ -0,0 +1,34 @@ 
+// { dg-do compile }
+// { dg-options "-Wall -Werror" }
+// a.cc:11:3: error: 'B::B' names the constructor, not the type
+// a.cc:11:8: error: expected ';' before 'f'
+// a.cc:11:13: error: statement cannot resolve address of overloaded function
+// a.cc:18:1: error: control reaches end of non-void function [-Werror=return-type]
+ 
+
+// After a parsing error, the IL ends up in an inconsistent state.
+// In this case, the parser never adds destructor calls, which causes
+// B::~B to never be called, triggering the error 'control reaches end
+// of non-void function' from the middle end. This second error is
+// bogus and only confuses the user.
+
+int bar(int);
+
+struct B {
+    B(int);
+    ~B() __attribute__((noreturn));
+};
+
+
+int foo(void)
+{
+  B::B f(10);	// { dg-error "names the constructor" }
+		// { dg-error "expected ';'" "" { target *-*-* } 25 }
+		// { dg-error "cannot resolve" "" { target *-*-* } 25 }
+  return 0;
+}
+
+int bar(int j)
+{
+  B(10);
+}
Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c	(revision 175523)
+++ gcc/tree-cfg.c	(working copy)
@@ -7445,12 +7445,28 @@  extract_true_false_edges_from_block (bas
     }
 }
 
+static bool
+gate_warn_function_return (void)
+{
+  /* FIXME - Disable this warning if there were errors upstream
+     (Google ref 4487457).  We should not even get this far down in
+     the optimization process after a syntax error in the parser.
+     However, bailing out right after parsing causes many regressions
+     in the testsuite, because tests expect more errors from the
+     compiler.
+
+     To avoid invasive changes in 4.6, the trunk variant of this fix
+     is described in http://gcc.gnu.org/ml/gcc/2011-06/msg00213.html.  */
+  return !seen_error ();
+}
+
+
 struct gimple_opt_pass pass_warn_function_return =
 {
  {
   GIMPLE_PASS,
   "*warn_function_return",		/* name */
-  NULL,					/* gate */
+  gate_warn_function_return,		/* gate */
   execute_warn_function_return,		/* execute */
   NULL,					/* sub */
   NULL,					/* next */