compiler: Implement 3-index slicing.

From-SVN: r204034

gcc/go/gofrontend/expressions.h

@@ -232,19 +232,21 @@ class Expression
 		    Named_object* function, Location);
 
   // Make an index or slice expression.  This is a parser expression
-  // which represents LEFT[START:END].  END may be NULL, meaning an
-  // index rather than a slice.  At parse time we may not know the
-  // type of LEFT.  After parsing this is lowered to an array index, a
-  // string index, or a map index.
+  // which represents LEFT[START:END:CAP].  END may be NULL, meaning an
+  // index rather than a slice.  CAP may be NULL, meaning we use the default
+  // capacity of LEFT. At parse time we may not know the type of LEFT.
+  // After parsing this is lowered to an array index, a string index,
+  // or a map index.
   static Expression*
   make_index(Expression* left, Expression* start, Expression* end,
-	     Location);
+             Expression* cap, Location);
 
   // Make an array index expression.  END may be NULL, in which case
-  // this is an lvalue.
+  // this is an lvalue.  CAP may be NULL, in which case it defaults
+  // to cap(ARRAY).
   static Expression*
   make_array_index(Expression* array, Expression* start, Expression* end,
-		   Location);
+                   Expression* cap, Location);
 
   // Make a string index expression.  END may be NULL.  This is never
   // an lvalue.
@@ -1672,9 +1674,9 @@ class Index_expression : public Parser_expression
 {
  public:
   Index_expression(Expression* left, Expression* start, Expression* end,
-		   Location location)
+                   Expression* cap, Location location)
     : Parser_expression(EXPRESSION_INDEX, location),
-      left_(left), start_(start), end_(end), is_lvalue_(false)
+      left_(left), start_(start), end_(end), cap_(cap), is_lvalue_(false)
   { }
 
   // Record that this expression is an lvalue.
@@ -1683,10 +1685,11 @@ class Index_expression : public Parser_expression
   { this->is_lvalue_ = true; }
 
   // Dump an index expression, i.e. an expression of the form
-  // expr[expr] or expr[expr:expr], to a dump context.
+  // expr[expr], expr[expr:expr], or expr[expr:expr:expr] to a dump context.
   static void
   dump_index_expression(Ast_dump_context*, const Expression* expr, 
-                        const Expression* start, const Expression* end);
+                        const Expression* start, const Expression* end,
+                        const Expression* cap);
 
  protected:
   int
@@ -1702,6 +1705,9 @@ class Index_expression : public Parser_expression
 				(this->end_ == NULL
 				 ? NULL
 				 : this->end_->copy()),
+				(this->cap_ == NULL
+				 ? NULL
+				 : this->cap_->copy()),
 				this->location());
   }
 
@@ -1723,6 +1729,10 @@ class Index_expression : public Parser_expression
   // The second index.  This is NULL for an index, non-NULL for a
   // slice.
   Expression* end_;
+  // The capacity argument.  This is NULL for indices and slices that use the
+  // default capacity, non-NULL for indices and slices that specify the
+  // capacity.
+  Expression* cap_;
   // Whether this is being used as an l-value.  We set this during the
   // parse because map index expressions need to know.
   bool is_lvalue_;

gcc/go/gofrontend/parse.cc

@@ -3152,7 +3152,7 @@ Parse::selector(Expression* left, bool* is_type_switch)
 }
 
 // Index          = "[" Expression "]" .
-// Slice          = "[" Expression ":" [ Expression ] "]" .
+// Slice          = "[" Expression ":" [ Expression ] [ ":" Expression ] "]" .
 
 Expression*
 Parse::index(Expression* expr)
@@ -3178,14 +3178,31 @@ Parse::index(Expression* expr)
       // We use nil to indicate a missing high expression.
       if (this->advance_token()->is_op(OPERATOR_RSQUARE))
 	end = Expression::make_nil(this->location());
+      else if (this->peek_token()->is_op(OPERATOR_COLON))
+	{
+	  error_at(this->location(), "middle index required in 3-index slice");
+	  end = Expression::make_error(this->location());
+	}
       else
 	end = this->expression(PRECEDENCE_NORMAL, false, true, NULL, NULL);
     }
+
+  Expression* cap = NULL;
+  if (this->peek_token()->is_op(OPERATOR_COLON))
+    {
+      if (this->advance_token()->is_op(OPERATOR_RSQUARE))
+	{
+	  error_at(this->location(), "final index required in 3-index slice");
+	  cap = Expression::make_error(this->location());
+	}
+      else
+        cap = this->expression(PRECEDENCE_NORMAL, false, true, NULL, NULL);
+    }
   if (!this->peek_token()->is_op(OPERATOR_RSQUARE))
     error_at(this->location(), "missing %<]%>");
   else
     this->advance_token();
-  return Expression::make_index(expr, start, end, location);
+  return Expression::make_index(expr, start, end, cap, location);
 }
 
 // Call           = "(" [ ArgumentList [ "," ] ] ")" .

gcc/go/gofrontend/statements.cc

@@ -5540,7 +5540,7 @@ For_range_statement::lower_range_array(Gogo* gogo,
 
       ref = this->make_range_ref(range_object, range_temp, loc);
       Expression* ref2 = Expression::make_temporary_reference(index_temp, loc);
-      Expression* index = Expression::make_index(ref, ref2, NULL, loc);
+      Expression* index = Expression::make_index(ref, ref2, NULL, NULL, loc);
 
       tref = Expression::make_temporary_reference(value_temp, loc);
       tref->set_is_lvalue();
@@ -5641,7 +5641,7 @@ For_range_statement::lower_range_slice(Gogo* gogo,
 
       ref = Expression::make_temporary_reference(for_temp, loc);
       Expression* ref2 = Expression::make_temporary_reference(index_temp, loc);
-      Expression* index = Expression::make_index(ref, ref2, NULL, loc);
+      Expression* index = Expression::make_index(ref, ref2, NULL, NULL, loc);
 
       tref = Expression::make_temporary_reference(value_temp, loc);
       tref->set_is_lvalue();
@@ -5849,7 +5849,7 @@ For_range_statement::lower_range_map(Gogo*,
   Expression* zexpr = Expression::make_integer(&zval, NULL, loc);
   mpz_clear(zval);
 
-  Expression* index = Expression::make_index(ref, zexpr, NULL, loc);
+  Expression* index = Expression::make_index(ref, zexpr, NULL, NULL, loc);
 
   Expression* ne = Expression::make_binary(OPERATOR_NOTEQ, index,
 					   Expression::make_nil(loc),

gcc/go/gofrontend/types.cc

@@ -5645,12 +5645,12 @@ Array_type::write_equal_function(Gogo* gogo, Named_type* name)
   Expression* e1 = Expression::make_temporary_reference(p1, bloc);
   e1 = Expression::make_unary(OPERATOR_MULT, e1, bloc);
   ref = Expression::make_temporary_reference(index, bloc);
-  e1 = Expression::make_array_index(e1, ref, NULL, bloc);
+  e1 = Expression::make_array_index(e1, ref, NULL, NULL, bloc);
 
   Expression* e2 = Expression::make_temporary_reference(p2, bloc);
   e2 = Expression::make_unary(OPERATOR_MULT, e2, bloc);
   ref = Expression::make_temporary_reference(index, bloc);
-  e2 = Expression::make_array_index(e2, ref, NULL, bloc);
+  e2 = Expression::make_array_index(e2, ref, NULL, NULL, bloc);
 
   Expression* cond = Expression::make_binary(OPERATOR_NOTEQ, e1, e2, bloc);