Go patch committed: Compare slice start and end with cap, not len

[Ian Lance Taylor]

The Go spec says that in a slice expression, the start and end indexes
are compared with the capacity of the slice value being sliced, not its
length.  Somehow gccgo was doing OK getting that wrong.  This patch
fixes it.  Bootstrapped and ran Go testsuite on
x86_64-unknown-linux-gnu.  Committed to mainline.

Ian


diff -r ce6462aab400 go/expressions.cc
--- a/go/expressions.cc	Thu Feb 02 10:30:35 2012 -0800
+++ b/go/expressions.cc	Thu Feb 02 13:15:49 2012 -0800
@@ -10649,11 +10649,28 @@
 
   if (array_type->length() == NULL && !DECL_P(array_tree))
     array_tree = save_expr(array_tree);
-  tree length_tree = array_type->length_tree(gogo, array_tree);
-  if (length_tree == error_mark_node)
-    return error_mark_node;
-  length_tree = save_expr(length_tree);
-  tree length_type = TREE_TYPE(length_tree);
+
+  tree length_tree = NULL_TREE;
+  if (this->end_ == NULL || this->end_->is_nil_expression())
+    {
+      length_tree = array_type->length_tree(gogo, array_tree);
+      if (length_tree == error_mark_node)
+	return error_mark_node;
+      length_tree = save_expr(length_tree);
+    }
+
+  tree capacity_tree = NULL_TREE;
+  if (this->end_ != NULL)
+    {
+      capacity_tree = array_type->capacity_tree(gogo, array_tree);
+      if (capacity_tree == error_mark_node)
+	return error_mark_node;
+      capacity_tree = save_expr(capacity_tree);
+    }
+
+  tree length_type = (length_tree != NULL_TREE
+		      ? TREE_TYPE(length_tree)
+		      : TREE_TYPE(capacity_tree));
 
   tree bad_index = boolean_false_node;
 
@@ -10676,7 +10693,9 @@
 					       ? GE_EXPR
 					       : GT_EXPR),
 					      boolean_type_node, start_tree,
-					      length_tree));
+					      (this->end_ == NULL
+					       ? length_tree
+					       : capacity_tree)));
 
   int code = (array_type->length() != NULL
 	      ? (this->end_ == NULL
@@ -10723,12 +10742,6 @@
 
   // Array slice.
 
-  tree capacity_tree = array_type->capacity_tree(gogo, array_tree);
-  if (capacity_tree == error_mark_node)
-    return error_mark_node;
-  capacity_tree = fold_convert_loc(loc.gcc_location(), length_type,
-                                   capacity_tree);
-
   tree end_tree;
   if (this->end_->is_nil_expression())
     end_tree = length_tree;
@@ -10747,7 +10760,6 @@
 
       end_tree = fold_convert_loc(loc.gcc_location(), length_type, end_tree);
 
-      capacity_tree = save_expr(capacity_tree);
       tree bad_end = fold_build2_loc(loc.gcc_location(), TRUTH_OR_EXPR,
                                      boolean_type_node,
 				     fold_build2_loc(loc.gcc_location(),
diff -r ce6462aab400 go/types.cc
--- a/go/types.cc	Thu Feb 02 10:30:35 2012 -0800
+++ b/go/types.cc	Thu Feb 02 13:15:49 2012 -0800
@@ -5416,7 +5416,8 @@
 Array_type::capacity_tree(Gogo* gogo, tree array)
 {
   if (this->length_ != NULL)
-    return omit_one_operand(sizetype, this->get_length_tree(gogo), array);
+    return omit_one_operand(integer_type_node, this->get_length_tree(gogo),
+			    array);
 
   // This is an open array.  We need to read the capacity field.