Use temporary variables for calls with multiple results.

From-SVN: r176998

gcc/go/gofrontend/expressions.h

@@ -15,6 +15,7 @@
 class Gogo;
 class Translate_context;
 class Traverse;
+class Statement_inserter;
 class Type;
 struct Type_context;
 class Function_type;
@@ -128,7 +129,7 @@ class Expression
   // Make a reference to a temporary variable.  Temporary variables
   // are always created by a single statement, which is what we use to
   // refer to them.
-  static Expression*
+  static Temporary_reference_expression*
   make_temporary_reference(Temporary_statement*, source_location);
 
   // Make a sink expression--a reference to the blank identifier _.
@@ -521,13 +522,18 @@ class Expression
   traverse_subexpressions(Traverse*);
 
   // Lower an expression.  This is called immediately after parsing.
-  // IOTA_VALUE is the value that we should give to any iota
-  // expressions.  This function must resolve expressions which could
-  // not be fully parsed into their final form.  It returns the same
-  // Expression or a new one.
+  // FUNCTION is the function we are in; it will be NULL for an
+  // expression initializing a global variable.  INSERTER may be used
+  // to insert statements before the statement or initializer
+  // containing this expression; it is normally used to create
+  // temporary variables.  IOTA_VALUE is the value that we should give
+  // to any iota expressions.  This function must resolve expressions
+  // which could not be fully parsed into their final form.  It
+  // returns the same Expression or a new one.
   Expression*
-  lower(Gogo* gogo, Named_object* function, int iota_value)
-  { return this->do_lower(gogo, function, iota_value); }
+  lower(Gogo* gogo, Named_object* function, Statement_inserter* inserter,
+	int iota_value)
+  { return this->do_lower(gogo, function, inserter, iota_value); }
 
   // Determine the real type of an expression with abstract integer,
   // floating point, or complex type.  TYPE_CONTEXT describes the
@@ -636,7 +642,7 @@ class Expression
 
   // Return a lowered expression.
   virtual Expression*
-  do_lower(Gogo*, Named_object*, int)
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int)
   { return this; }
 
   // Return whether this is a constant expression.
@@ -871,7 +877,7 @@ class Parser_expression : public Expression
 
  protected:
   virtual Expression*
-  do_lower(Gogo*, Named_object*, int) = 0;
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int) = 0;
 
   Type*
   do_type();
@@ -906,7 +912,7 @@ class Var_expression : public Expression
 
  protected:
   Expression*
-  do_lower(Gogo*, Named_object*, int);
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int);
 
   Type*
   do_type();
@@ -941,9 +947,15 @@ class Temporary_reference_expression : public Expression
   Temporary_reference_expression(Temporary_statement* statement,
 				 source_location location)
     : Expression(EXPRESSION_TEMPORARY_REFERENCE, location),
-      statement_(statement)
+      statement_(statement), is_lvalue_(false)
   { }
 
+  // Indicate that this reference appears on the left hand side of an
+  // assignment statement.
+  void
+  set_is_lvalue()
+  { this->is_lvalue_ = true; }
+
  protected:
   Type*
   do_type();
@@ -969,6 +981,9 @@ class Temporary_reference_expression : public Expression
  private:
   // The statement where the temporary variable is defined.
   Temporary_statement* statement_;
+  // Whether this reference appears on the left hand side of an
+  // assignment statement.
+  bool is_lvalue_;
 };
 
 // A string expression.
@@ -1099,7 +1114,7 @@ class Binary_expression : public Expression
   do_traverse(Traverse* traverse);
 
   Expression*
-  do_lower(Gogo*, Named_object*, int);
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int);
 
   bool
   do_is_constant() const
@@ -1156,9 +1171,9 @@ class Call_expression : public Expression
   Call_expression(Expression* fn, Expression_list* args, bool is_varargs,
 		  source_location location)
     : Expression(EXPRESSION_CALL, location),
-      fn_(fn), args_(args), type_(NULL), tree_(NULL), is_varargs_(is_varargs),
-      varargs_are_lowered_(false), types_are_determined_(false),
-      is_deferred_(false)
+      fn_(fn), args_(args), type_(NULL), results_(NULL), tree_(NULL),
+      is_varargs_(is_varargs), varargs_are_lowered_(false),
+      types_are_determined_(false), is_deferred_(false), issued_error_(false)
   { }
 
   // The function to call.
@@ -1183,6 +1198,12 @@ class Call_expression : public Expression
   size_t
   result_count() const;
 
+  // Return the temporary variable which holds result I.  This is only
+  // valid after the expression has been lowered, and is only valid
+  // for calls which return multiple results.
+  Temporary_statement*
+  result(size_t i) const;
+
   // Return whether this is a call to the predeclared function
   // recover.
   bool
@@ -1207,12 +1228,17 @@ class Call_expression : public Expression
   set_is_deferred()
   { this->is_deferred_ = true; }
 
+  // We have found an error with this call expression; return true if
+  // we should report it.
+  bool
+  issue_error();
+
  protected:
   int
   do_traverse(Traverse*);
 
   virtual Expression*
-  do_lower(Gogo*, Named_object*, int);
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int);
 
   void
   do_discarding_value()
@@ -1256,8 +1282,8 @@ class Call_expression : public Expression
 
   // Let a builtin expression lower varargs.
   Expression*
-  lower_varargs(Gogo*, Named_object* function, Type* varargs_type,
-		size_t param_count);
+  lower_varargs(Gogo*, Named_object* function, Statement_inserter* inserter,
+		Type* varargs_type, size_t param_count);
 
   // Let a builtin expression check whether types have been
   // determined.
@@ -1276,6 +1302,9 @@ class Call_expression : public Expression
 			    Interface_field_reference_expression*,
 			    tree*);
 
+  tree
+  set_results(Translate_context*, tree);
+
   // The function to call.
   Expression* fn_;
   // The arguments to pass.  This may be NULL if there are no
@@ -1283,6 +1312,9 @@ class Call_expression : public Expression
   Expression_list* args_;
   // The type of the expression, to avoid recomputing it.
   Type* type_;
+  // The list of temporaries which will hold the results if the
+  // function returns a tuple.
+  std::vector<Temporary_statement*>* results_;
   // The tree for the call, used for a call which returns a tuple.
   tree tree_;
   // True if the last argument is a varargs argument (f(a...)).
@@ -1293,6 +1325,10 @@ class Call_expression : public Expression
   bool types_are_determined_;
   // True if the call is an argument to a defer statement.
   bool is_deferred_;
+  // True if we reported an error about a mismatch between call
+  // results and uses.  This is to avoid producing multiple errors
+  // when there are multiple Call_result_expressions.
+  bool issued_error_;
 };
 
 // An expression which represents a pointer to a function.
@@ -1390,7 +1426,7 @@ class Unknown_expression : public Parser_expression
 
  protected:
   Expression*
-  do_lower(Gogo*, Named_object*, int);
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int);
 
   Expression*
   do_copy()
@@ -1425,7 +1461,7 @@ class Index_expression : public Parser_expression
   do_traverse(Traverse*);
 
   Expression*
-  do_lower(Gogo*, Named_object*, int);
+  do_lower(Gogo*, Named_object*, Statement_inserter*, int);
 
   Expression*
   do_copy()

gcc/go/gofrontend/gogo.h

@@ -8,6 +8,7 @@
 #define GO_GOGO_H
 
 class Traverse;
+class Statement_inserter;
 class Type;
 class Type_hash_identical;
 class Type_equal;
@@ -366,7 +367,7 @@ class Gogo
 
   // Lower an expression.
   void
-  lower_expression(Named_object* function, Expression**);
+  lower_expression(Named_object* function, Statement_inserter*, Expression**);
 
   // Lower a constant.
   void
@@ -1157,7 +1158,7 @@ class Variable
 
   // Lower the initialization expression after parsing is complete.
   void
-  lower_init_expression(Gogo*, Named_object*);
+  lower_init_expression(Gogo*, Named_object*, Statement_inserter*);
 
   // A special case: the init value is used only to determine the
   // type.  This is used if the variable is defined using := with the
@@ -1208,7 +1209,7 @@ class Variable
 
   // Traverse the initializer expression.
   int
-  traverse_expression(Traverse*);
+  traverse_expression(Traverse*, unsigned int traverse_mask);
 
   // Determine the type of the variable if necessary.
   void
@@ -2463,6 +2464,46 @@ class Traverse
   Expressions_seen* expressions_seen_;
 };
 
+// A class which makes it easier to insert new statements before the
+// current statement during a traversal.
+
+class Statement_inserter
+{
+ public:
+  // Empty constructor.
+  Statement_inserter()
+    : block_(NULL), pindex_(NULL), gogo_(NULL), var_(NULL)
+  { }
+
+  // Constructor for a statement in a block.
+  Statement_inserter(Block* block, size_t *pindex)
+    : block_(block), pindex_(pindex), gogo_(NULL), var_(NULL)
+  { }
+
+  // Constructor for a global variable.
+  Statement_inserter(Gogo* gogo, Variable* var)
+    : block_(NULL), pindex_(NULL), gogo_(gogo), var_(var)
+  { go_assert(var->is_global()); }
+
+  // We use the default copy constructor and assignment operator.
+
+  // Insert S before the statement we are traversing, or before the
+  // initialization expression of a global variable.
+  void
+  insert(Statement* s);
+
+ private:
+  // The block that the statement is in.
+  Block* block_;
+  // The index of the statement that we are traversing.
+  size_t* pindex_;
+  // The IR, needed when looking at an initializer expression for a
+  // global variable.
+  Gogo* gogo_;
+  // The global variable, when looking at an initializer expression.
+  Variable* var_;
+};
+
 // When translating the gogo IR into the backend data structure, this
 // is the context we pass down the blocks and statements.
 

gcc/go/gofrontend/statements.h

@@ -11,6 +11,7 @@
 
 class Gogo;
 class Traverse;
+class Statement_inserter;
 class Block;
 class Function;
 class Unnamed_label;
@@ -290,9 +291,11 @@ class Statement
   // simplify statements for further processing.  It returns the same
   // Statement or a new one.  FUNCTION is the function containing this
   // statement.  BLOCK is the block containing this statement.
+  // INSERTER can be used to insert new statements before this one.
   Statement*
-  lower(Gogo* gogo, Named_object* function, Block* block)
-  { return this->do_lower(gogo, function, block); }
+  lower(Gogo* gogo, Named_object* function, Block* block,
+	Statement_inserter* inserter)
+  { return this->do_lower(gogo, function, block, inserter); }
 
   // Set type information for unnamed constants.
   void
@@ -385,7 +388,7 @@ class Statement
   // Implemented by the child class: lower this statement to a simpler
   // one.
   virtual Statement*
-  do_lower(Gogo*, Named_object*, Block*)
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*)
   { return this; }
 
   // Implemented by child class: set type information for unnamed
@@ -535,6 +538,9 @@ class Variable_declaration_statement : public Statement
   bool
   do_traverse_assignments(Traverse_assignments*);
 
+  Statement*
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
+
   Bstatement*
   do_get_backend(Translate_context*);
 
@@ -566,7 +572,7 @@ class Return_statement : public Statement
   do_traverse_assignments(Traverse_assignments*);
 
   Statement*
-  do_lower(Gogo*, Named_object*, Block*);
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
 
   bool
   do_may_fall_through() const
@@ -806,7 +812,7 @@ class Select_statement : public Statement
   { return this->clauses_->traverse(traverse); }
 
   Statement*
-  do_lower(Gogo*, Named_object*, Block*);
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
 
   void
   do_determine_types()
@@ -993,7 +999,7 @@ class For_statement : public Statement
   { go_unreachable(); }
 
   Statement*
-  do_lower(Gogo*, Named_object*, Block*);
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
 
   Bstatement*
   do_get_backend(Translate_context*)
@@ -1051,7 +1057,7 @@ class For_range_statement : public Statement
   { go_unreachable(); }
 
   Statement*
-  do_lower(Gogo*, Named_object*, Block*);
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
 
   Bstatement*
   do_get_backend(Translate_context*)
@@ -1280,7 +1286,7 @@ class Switch_statement : public Statement
   do_traverse(Traverse*);
 
   Statement*
-  do_lower(Gogo*, Named_object*, Block*);
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
 
   Bstatement*
   do_get_backend(Translate_context*)
@@ -1426,7 +1432,7 @@ class Type_switch_statement : public Statement
   do_traverse(Traverse*);
 
   Statement*
-  do_lower(Gogo*, Named_object*, Block*);
+  do_lower(Gogo*, Named_object*, Block*, Statement_inserter*);
 
   Bstatement*
   do_get_backend(Translate_context*)