compiler: remove Array_index_expression::is_lvalue_

As of CL 77510 it is never true.

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/394695

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-fbadca004b1e09db177c8e071706841038d1dd64
+6a33e7e30c89edc12340dc470b44791bb1066feb
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/expressions.cc

@@ -7671,8 +7671,7 @@ Expression::comparison(Translate_context* context, Type* result_type,
 	  && left_type->array_type()->length() == NULL)
 	{
 	  Array_type* at = left_type->array_type();
-          bool is_lvalue = false;
-          left = at->get_value_pointer(context->gogo(), left, is_lvalue);
+          left = at->get_value_pointer(context->gogo(), left);
 	}
       else if (left_type->interface_type() != NULL)
 	{
@@ -9276,7 +9275,7 @@ Builtin_call_expression::flatten_append(Gogo* gogo, Named_object* function,
   Type* unsafe_ptr_type = Type::make_pointer_type(Type::make_void_type());
   Expression* a1 = Expression::make_type_descriptor(element_type, loc);
   Expression* a2 = Expression::make_temporary_reference(s1tmp, loc);
-  a2 = slice_type->array_type()->get_value_pointer(gogo, a2, false);
+  a2 = slice_type->array_type()->get_value_pointer(gogo, a2);
   a2 = Expression::make_cast(unsafe_ptr_type, a2, loc);
   Expression* a3 = Expression::make_temporary_reference(l1tmp, loc);
   Expression* a4 = Expression::make_temporary_reference(c1tmp, loc);
@@ -13848,9 +13847,8 @@ Array_index_expression::do_get_backend(Translate_context* context)
 	}
       else
 	{
-	  Expression* valptr =
-              array_type->get_value_pointer(gogo, this->array_,
-                                            this->is_lvalue_);
+	  Expression* valptr = array_type->get_value_pointer(gogo,
+							     this->array_);
 	  Bexpression* ptr = valptr->get_backend(context);
           ptr = gogo->backend()->pointer_offset_expression(ptr, start, loc);
 
@@ -13891,8 +13889,7 @@ Array_index_expression::do_get_backend(Translate_context* context)
   Bexpression* offset = gogo->backend()->conditional_expression(bfn, int_btype,
 								cond, zero,
 								start, loc);
-  Expression* valptr = array_type->get_value_pointer(gogo, this->array_,
-                                                     this->is_lvalue_);
+  Expression* valptr = array_type->get_value_pointer(gogo, this->array_);
   Bexpression* val = valptr->get_backend(context);
   val = gogo->backend()->pointer_offset_expression(val, offset, loc);
 

gcc/go/gofrontend/expressions.h

@@ -3055,7 +3055,7 @@ class Array_index_expression : public Expression
 			 Expression* end, Expression* cap, Location location)
     : Expression(EXPRESSION_ARRAY_INDEX, location),
       array_(array), start_(start), end_(end), cap_(cap), type_(NULL),
-      is_lvalue_(false), needs_bounds_check_(true), is_flattened_(false)
+      needs_bounds_check_(true), is_flattened_(false)
   { }
 
   // Return the array.
@@ -3087,18 +3087,6 @@ class Array_index_expression : public Expression
   end() const
   { return this->end_; }
 
-  // Return whether this array index expression appears in an lvalue
-  // (left hand side of assignment) context.
-  bool
-  is_lvalue() const
-  { return this->is_lvalue_; }
-
-  // Update this array index expression to indicate that it appears
-  // in a left-hand-side or lvalue context.
-  void
-  set_is_lvalue()
-  { this->is_lvalue_ = true; }
-
   void
   set_needs_bounds_check(bool b)
   { this->needs_bounds_check_ = b; }
@@ -3174,8 +3162,6 @@ class Array_index_expression : public Expression
   Expression* cap_;
   // The type of the expression.
   Type* type_;
-  // Whether expr appears in an lvalue context.
-  bool is_lvalue_;
   // Whether bounds check is needed.
   bool needs_bounds_check_;
   // Whether this has already been flattened.

gcc/go/gofrontend/types.cc

@@ -7815,7 +7815,7 @@ Array_type::finish_backend_element(Gogo* gogo)
 // Return an expression for a pointer to the values in ARRAY.
 
 Expression*
-Array_type::get_value_pointer(Gogo*, Expression* array, bool is_lvalue) const
+Array_type::get_value_pointer(Gogo*, Expression* array) const
 {
   if (this->length() != NULL)
     {
@@ -7828,25 +7828,6 @@ Array_type::get_value_pointer(Gogo*, Expression* array, bool is_lvalue) const
     }
 
   // Slice.
-
-  if (is_lvalue)
-    {
-      Temporary_reference_expression* tref =
-          array->temporary_reference_expression();
-      Var_expression* ve = array->var_expression();
-      if (tref != NULL)
-        {
-          tref = tref->copy()->temporary_reference_expression();
-          tref->set_is_lvalue();
-          array = tref;
-        }
-      else if (ve != NULL)
-        {
-          ve = new Var_expression(ve->named_object(), ve->location());
-          array = ve;
-        }
-    }
-
   return Expression::make_slice_info(array,
                                      Expression::SLICE_INFO_VALUE_POINTER,
                                      array->location());

gcc/go/gofrontend/types.h

@@ -2800,7 +2800,7 @@ class Array_type : public Type
 
   // Return an expression for the pointer to the values in an array.
   Expression*
-  get_value_pointer(Gogo*, Expression* array, bool is_lvalue) const;
+  get_value_pointer(Gogo*, Expression* array) const;
 
   // Return an expression for the length of an array with this type.
   Expression*