Go patch committed: return an error statement for fallthrough in last case

[Ian Lance Taylor]

This patch by Cherry Zhang changes the Go frontend to call
error_statement when generating GIMPLE for a fallthrough in the last
case in a switch.  This avoids generating incorrect IR in an erroneous
case.  Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.
Committed to mainline.

Ian

Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE     (revision 252849)
+++ gcc/go/gofrontend/MERGE     (working copy)
@@ -1,4 +1,4 @@
-de7b370901c4fc6852eaa7372282bb699429ec4a
+70cf67704699c8bcaf6f52437812367cdc4ad169
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: gcc/go/gofrontend/statements.cc
===================================================================
--- gcc/go/gofrontend/statements.cc     (revision 252749)
+++ gcc/go/gofrontend/statements.cc     (working copy)
@@ -3707,6 +3707,12 @@ Case_clauses::get_backend(Translate_cont
       std::vector<Bexpression*> cases;
       Bstatement* stat = p->get_backend(context, break_label, &case_constants,
                                        &cases);
+      // The final clause can't fall through.
+      if (i == c - 1 && p->is_fallthrough())
+        {
+          go_assert(saw_errors());
+          stat = context->backend()->error_statement();
+        }
       (*all_cases)[i].swap(cases);
       (*all_statements)[i] = stat;
     }