1 files changed, 88 insertions, 1 deletions

diff --git a/gcc/go/gofrontend/gogo.cc b/gcc/go/gofrontend/gogo.cc
index 0852186..b9c8fa9 100644
--- a/gcc/go/gofrontend/gogo.cc
+++ b/gcc/go/gofrontend/gogo.cc
@@ -41,6 +41,9 @@ Gogo::Gogo(Backend* backend, Linemap* linemap, int, int pointer_size)
     pkgpath_(),
     pkgpath_symbol_(),
     prefix_(),
+    zero_value_(NULL),
+    zero_value_size_(0),
+    zero_value_align_(0),
     pkgpath_set_(false),
     pkgpath_from_option_(false),
     prefix_from_option_(false),
@@ -575,6 +578,88 @@ Gogo::current_bindings() const
     return this->globals_;
 }
 
+// Return the special variable used as the zero value of types.
+
+Named_object*
+Gogo::zero_value(Type *type)
+{
+  if (this->zero_value_ == NULL)
+    {
+      Location bloc = Linemap::predeclared_location();
+
+      // We will change the type later, when we know the size.
+      Type* byte_type = this->lookup_global("byte")->type_value();
+
+      mpz_t val;
+      mpz_init_set_ui(val, 0);
+      Expression* zero = Expression::make_integer(&val, NULL, bloc);
+      mpz_clear(val);
+
+      Type* array_type = Type::make_array_type(byte_type, zero);
+
+      Variable* var = new Variable(array_type, NULL, true, false, false, bloc);
+      this->zero_value_ = Named_object::make_variable("go$zerovalue", NULL,
+						      var);
+    }
+
+  // The zero value will be the maximum required size.
+  unsigned long size;
+  bool ok = type->backend_type_size(this, &size);
+  if (!ok) {
+    go_assert(saw_errors());
+    size = 4;
+  }
+  if (size > this->zero_value_size_)
+    this->zero_value_size_ = size;
+
+  unsigned long align;
+  ok = type->backend_type_align(this, &align);
+  if (!ok) {
+    go_assert(saw_errors());
+    align = 4;
+  }
+  if (align > this->zero_value_align_)
+    this->zero_value_align_ = align;
+
+  return this->zero_value_;
+}
+
+// Return whether V is the zero value variable.
+
+bool
+Gogo::is_zero_value(Variable* v) const
+{
+  return this->zero_value_ != NULL && this->zero_value_->var_value() == v;
+}
+
+// Return the backend variable for the special zero value, or NULL if
+// it is not needed.
+
+Bvariable*
+Gogo::backend_zero_value()
+{
+  if (this->zero_value_ == NULL)
+    return NULL;
+
+  Type* byte_type = this->lookup_global("byte")->type_value();
+  Btype* bbtype_type = byte_type->get_backend(this);
+
+  Type* int_type = this->lookup_global("int")->type_value();
+  Btype* bint_type = int_type->get_backend(this);
+
+  mpz_t val;
+  mpz_init_set_ui(val, this->zero_value_size_);
+  Bexpression* blength =
+    this->backend()->integer_constant_expression(bint_type, val);
+  mpz_clear(val);
+
+  Btype* barray_type = this->backend()->array_type(bbtype_type, blength);
+
+  return this->backend()->implicit_variable(this->zero_value_->name(),
+					    barray_type, NULL, true, true,
+					    this->zero_value_align_);
+}
+
 // Add statements to INIT_STMTS which run the initialization
 // functions for imported packages.  This is only used for the "main"
 // package.
@@ -6078,7 +6163,9 @@ Variable::get_backend_variable(Gogo* gogo, Named_object* function,
 	  Btype* btype = type->get_backend(gogo);
 
 	  Bvariable* bvar;
-	  if (this->is_global_)
+	  if (gogo->is_zero_value(this))
+	    bvar = gogo->backend_zero_value();
+	  else if (this->is_global_)
 	    bvar = backend->global_variable((package == NULL
 					     ? gogo->package_name()
 					     : package->package_name()),