compiler: omit a couple of write barriers

    
    Omit a write barrier for
        s = s[0:]
    for a slice s.  In this case the pointer is not changing and no write
    barrier is required.
    
    Omit a write barrier for
        s = append(s, v)
    in the case where len(s) < cap(s) (and similarly when appending more
    values).  When the slice has enough capacity the pointer is not
    changing and no write barrier is required.
    
    These changes are required to avoid write barriers in the method
    randomOrder.reset in the runtime package.  That method is called from
    procresize, at a point where we do not want to allocate memory.
    Otherwise that method can use a write barrier, allocate memory, and
    break TestReadMemStats.
    
    Reviewed-on: https://go-review.googlesource.com/134219

From-SVN: r264259

1 files changed, 9 insertions, 2 deletions

diff --git a/gcc/go/gofrontend/expressions.h b/gcc/go/gofrontend/expressions.h
index 5fa4171..f53cc6e 100644
--- a/gcc/go/gofrontend/expressions.h
+++ b/gcc/go/gofrontend/expressions.h
@@ -869,6 +869,11 @@ class Expression
   bool
   is_local_variable() const;
 
+  // Return true if two expressions refer to the same variable or
+  // struct field.
+  static bool
+  is_same_variable(Expression*, Expression*);
+
   // Make the builtin function descriptor type, so that it can be
   // converted.
   static void
@@ -2402,6 +2407,10 @@ class Builtin_call_expression : public Call_expression
   static bool
   array_len_is_constant(Expression* expr);
 
+  Expression*
+  flatten_append(Gogo*, Named_object*, Statement_inserter*, Expression*,
+		 Block*);
+
  protected:
   // This overrides Call_expression::do_lower.
   Expression*
@@ -2459,8 +2468,6 @@ class Builtin_call_expression : public Call_expression
   Expression*
   lower_make(Statement_inserter*);
 
-  Expression* flatten_append(Gogo*, Named_object*, Statement_inserter*);
-
   bool
   check_int_value(Expression*, bool is_length, bool* small);