compiler: pass lvalue/rvalue context to back end for var exprs

    
    Add a new flag on the Var_expression class that indicates
    whether the var reference appears in an "lvalue" context
    (for example, on the LHS of an assignment stmt) or an
    "rvalue" context (for example, as an argument of a call).
    
    Add a traversal pass that visits assignment stmt LHS subtrees
    so as to mark things prior to backend gen. Select the right
    context value in other places where Backend::var_expression is
    called.
    
    Reviewed-on: https://go-review.googlesource.com/33990

	* go-gcc.cc (Gcc_backend::var_expression): Add Varexpr_context
	parameter.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@243321 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 26 insertions, 18 deletions

diff --git a/gcc/go/gofrontend/expressions.cc b/gcc/go/gofrontend/expressions.cc
index 9740d324a86..24f6b125c7d 100644
--- a/gcc/go/gofrontend/expressions.cc
+++ b/gcc/go/gofrontend/expressions.cc
@@ -760,7 +760,8 @@ Var_expression::do_get_backend(Translate_context* context)
   else
     go_unreachable();
 
-  Bexpression* ret = context->backend()->var_expression(bvar, loc);
+  Bexpression* ret =
+      context->backend()->var_expression(bvar, this->in_lvalue_pos_, loc);
   if (is_in_heap)
     ret = context->backend()->indirect_expression(btype, ret, true, loc);
   return ret;
@@ -887,7 +888,10 @@ Temporary_reference_expression::do_get_backend(Translate_context* context)
 {
   Gogo* gogo = context->gogo();
   Bvariable* bvar = this->statement_->get_backend_variable(context);
-  Bexpression* ret = gogo->backend()->var_expression(bvar, this->location());
+  Varexpr_context ve_ctxt = (this->is_lvalue_ ? VE_lvalue : VE_rvalue);
+
+  Bexpression* ret = gogo->backend()->var_expression(bvar, ve_ctxt,
+                                                     this->location());
 
   // The backend can't always represent the same set of recursive types
   // that the Go frontend can.  In some cases this means that a
@@ -958,11 +962,11 @@ Set_and_use_temporary_expression::do_get_backend(Translate_context* context)
   Location loc = this->location();
   Gogo* gogo = context->gogo();
   Bvariable* bvar = this->statement_->get_backend_variable(context);
-  Bexpression* var_ref = gogo->backend()->var_expression(bvar, loc);
+  Bexpression* lvar_ref = gogo->backend()->var_expression(bvar, VE_rvalue, loc);
 
   Bexpression* bexpr = this->expr_->get_backend(context);
-  Bstatement* set = gogo->backend()->assignment_statement(var_ref, bexpr, loc);
-  var_ref = gogo->backend()->var_expression(bvar, loc);
+  Bstatement* set = gogo->backend()->assignment_statement(lvar_ref, bexpr, loc);
+  Bexpression* var_ref = gogo->backend()->var_expression(bvar, VE_lvalue, loc);
   Bexpression* ret = gogo->backend()->compound_expression(set, var_ref, loc);
   return ret;
 }
@@ -1065,11 +1069,12 @@ Sink_expression::do_get_backend(Translate_context* context)
       this->bvar_ =
 	gogo->backend()->temporary_variable(fn_ctx, context->bblock(), bt, NULL,
 					    false, loc, &decl);
-      Bexpression* var_ref = gogo->backend()->var_expression(this->bvar_, loc);
+      Bexpression* var_ref =
+          gogo->backend()->var_expression(this->bvar_, VE_lvalue, loc);
       var_ref = gogo->backend()->compound_expression(decl, var_ref, loc);
       return var_ref;
     }
-  return gogo->backend()->var_expression(this->bvar_, loc);
+  return gogo->backend()->var_expression(this->bvar_, VE_lvalue, loc);
 }
 
 // Ast dump for sink expression.
@@ -1276,7 +1281,7 @@ Func_descriptor_expression::do_get_backend(Translate_context* context)
   Named_object* no = this->fn_;
   Location loc = no->location();
   if (this->dvar_ != NULL)
-    return context->backend()->var_expression(this->dvar_, loc);
+    return context->backend()->var_expression(this->dvar_, VE_rvalue, loc);
 
   Gogo* gogo = context->gogo();
   std::string var_name;
@@ -1330,7 +1335,7 @@ Func_descriptor_expression::do_get_backend(Translate_context* context)
     }
 
   this->dvar_ = bvar;
-  return gogo->backend()->var_expression(bvar, loc);
+  return gogo->backend()->var_expression(bvar, VE_rvalue, loc);
 }
 
 // Print a function descriptor expression.
@@ -4207,7 +4212,8 @@ Unary_expression::do_get_backend(Translate_context* context)
 	{
 	  Temporary_statement* temp = sut->temporary();
 	  Bvariable* bvar = temp->get_backend_variable(context);
-          Bexpression* bvar_expr = gogo->backend()->var_expression(bvar, loc);
+          Bexpression* bvar_expr =
+              gogo->backend()->var_expression(bvar, VE_lvalue, loc);
           Bexpression* bval = sut->expression()->get_backend(context);
 
           Bstatement* bassign =
@@ -4294,7 +4300,7 @@ Unary_expression::do_get_backend(Translate_context* context)
 	  gogo->backend()->implicit_variable_set_init(implicit, buf, btype,
 						      true, copy_to_heap, false,
 						      bexpr);
-	  bexpr = gogo->backend()->var_expression(implicit, loc);
+	  bexpr = gogo->backend()->var_expression(implicit, VE_lvalue, loc);
 
 	  // If we are not copying a slice initializer to the heap,
 	  // then it can be changed by the program, so if it can
@@ -4304,7 +4310,7 @@ Unary_expression::do_get_backend(Translate_context* context)
 	      && this->expr_->type()->has_pointer())
 	    {
 	      Bexpression* root =
-		gogo->backend()->var_expression(implicit, loc);
+                  gogo->backend()->var_expression(implicit, VE_lvalue, loc);
 	      root = gogo->backend()->address_expression(root, loc);
 	      Type* type = Type::make_pointer_type(this->expr_->type());
 	      gogo->add_gc_root(Expression::make_backend(root, type, loc));
@@ -4324,7 +4330,7 @@ Unary_expression::do_get_backend(Translate_context* context)
                                                 true, false, btype, loc);
           gogo->backend()->immutable_struct_set_init(decl, buf, true, false,
                                                      btype, loc, bexpr);
-          bexpr = gogo->backend()->var_expression(decl, loc);
+          bexpr = gogo->backend()->var_expression(decl, VE_lvalue, loc);
         }
 
       go_assert(!this->create_temp_ || this->expr_->is_variable());
@@ -14116,7 +14122,7 @@ Heap_expression::do_get_backend(Translate_context* context)
   Bvariable* space_temp =
     gogo->backend()->temporary_variable(fndecl, context->bblock(), btype,
 					space, true, loc, &decl);
-  space = gogo->backend()->var_expression(space_temp, loc);
+  space = gogo->backend()->var_expression(space_temp, VE_lvalue, loc);
   Btype* expr_btype = this->expr_->type()->get_backend(gogo);
   Bexpression* ref =
     gogo->backend()->indirect_expression(expr_btype, space, true, loc);
@@ -14124,7 +14130,7 @@ Heap_expression::do_get_backend(Translate_context* context)
   Bexpression* bexpr = this->expr_->get_backend(context);
   Bstatement* assn = gogo->backend()->assignment_statement(ref, bexpr, loc);
   decl = gogo->backend()->compound_statement(decl, assn);
-  space = gogo->backend()->var_expression(space_temp, loc);
+  space = gogo->backend()->var_expression(space_temp, VE_rvalue, loc);
   return gogo->backend()->compound_expression(decl, space, loc);
 }
 
@@ -15063,7 +15069,8 @@ Interface_mtable_expression::do_get_backend(Translate_context* context)
   Gogo* gogo = context->gogo();
   Location loc = Linemap::predeclared_location();
   if (this->bvar_ != NULL)
-    return gogo->backend()->var_expression(this->bvar_, this->location());
+    return gogo->backend()->var_expression(this->bvar_, VE_rvalue,
+                                           this->location());
 
   const Typed_identifier_list* interface_methods = this->itype_->methods();
   go_assert(!interface_methods->empty());
@@ -15099,7 +15106,8 @@ Interface_mtable_expression::do_get_backend(Translate_context* context)
       this->bvar_ =
           gogo->backend()->immutable_struct_reference(mangled_name, asm_name,
                                                       btype, loc);
-      return gogo->backend()->var_expression(this->bvar_, this->location());
+      return gogo->backend()->var_expression(this->bvar_, VE_rvalue,
+                                             this->location());
     }
 
   // The first element is the type descriptor.
@@ -15147,7 +15155,7 @@ Interface_mtable_expression::do_get_backend(Translate_context* context)
 						  !is_public, btype, loc);
   gogo->backend()->immutable_struct_set_init(this->bvar_, mangled_name, false,
                                              !is_public, btype, loc, ctor);
-  return gogo->backend()->var_expression(this->bvar_, loc);
+  return gogo->backend()->var_expression(this->bvar_, VE_lvalue, loc);
 }
 
 void