compiler: make top-level decl for address-taken non-escaping locals

    
    If a local variable's address is taken and passed out of its
    lexical scope, GCC backend may reuse the stack slot for the
    variable, not knowing it is still live through a pointer. In
    this case, we create a top-level temporary variable and let the
    user-defined variable refer to the temporary variable as its
    storage location. As the temporary variable is declared at the
    top level, its stack slot will remain live throughout the
    function.
    
    Reviewed-on: https://go-review.googlesource.com/84675

	* go-gcc.cc (local_variable): Add decl_var parameter.

From-SVN: r256398

1 files changed, 39 insertions, 5 deletions

diff --git a/gcc/go/gofrontend/gogo.cc b/gcc/go/gofrontend/gogo.cc
index b1c7807..cdb8b18 100644
--- a/gcc/go/gofrontend/gogo.cc
+++ b/gcc/go/gofrontend/gogo.cc
@@ -3876,6 +3876,29 @@ Flatten::variable(Named_object* no)
       return TRAVERSE_CONTINUE;
     }
 
+  if (!no->var_value()->is_parameter()
+      && !no->var_value()->is_receiver()
+      && !no->var_value()->is_closure()
+      && no->var_value()->is_non_escaping_address_taken()
+      && !no->var_value()->is_in_heap()
+      && no->var_value()->toplevel_decl() == NULL)
+    {
+      // Local variable that has address taken but not escape.
+      // It needs to be live beyond its lexical scope. So we
+      // create a top-level declaration for it.
+      // No need to do it if it is already in the top level.
+      Block* top_block = function_->func_value()->block();
+      if (top_block->bindings()->lookup_local(no->name()) != no)
+        {
+          Variable* var = no->var_value();
+          Temporary_statement* ts =
+            Statement::make_temporary(var->type(), NULL, var->location());
+          ts->set_is_address_taken();
+          top_block->add_statement_at_front(ts);
+          var->set_toplevel_decl(ts);
+        }
+    }
+
   go_assert(!no->var_value()->has_pre_init());
 
   return TRAVERSE_SKIP_COMPONENTS;
@@ -6174,7 +6197,8 @@ Variable::Variable(Type* type, Expression* init, bool is_global,
     type_from_init_tuple_(false), type_from_range_index_(false),
     type_from_range_value_(false), type_from_chan_element_(false),
     is_type_switch_var_(false), determined_type_(false),
-    in_unique_section_(false), escapes_(true)
+    in_unique_section_(false), escapes_(true),
+    toplevel_decl_(NULL)
 {
   go_assert(type != NULL || init != NULL);
   go_assert(!is_parameter || init == NULL);
@@ -6751,9 +6775,19 @@ Variable::get_backend_variable(Gogo* gogo, Named_object* function,
 						   is_address_taken,
 						   this->location_);
 	      else
-		bvar = backend->local_variable(bfunction, n, btype,
-					       is_address_taken,
-					       this->location_);
+                {
+                  Bvariable* bvar_decl = NULL;
+                  if (this->toplevel_decl_ != NULL)
+                    {
+                      Translate_context context(gogo, NULL, NULL, NULL);
+                      bvar_decl = this->toplevel_decl_->temporary_statement()
+                        ->get_backend_variable(&context);
+                    }
+                  bvar = backend->local_variable(bfunction, n, btype,
+                                                 bvar_decl,
+                                                 is_address_taken,
+                                                 this->location_);
+                }
 	    }
 	  this->backend_ = bvar;
 	}
@@ -6785,7 +6819,7 @@ Result_variable::get_backend_variable(Gogo* gogo, Named_object* function,
 	  bool is_address_taken = (this->is_non_escaping_address_taken_
 				   && !this->is_in_heap());
 	  this->backend_ = backend->local_variable(bfunction, n, btype,
-						   is_address_taken,
+						   NULL, is_address_taken,
 						   this->location_);
 	}
     }