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Go patch committed: Don't initialize zero-sized fields in constructors

Message ID CAOyqgcUzo+M2Jh8BRP8MSVXQeGByAMaH54PJXu2fULhHzkGC-A@mail.gmail.com
State New
Headers show

Commit Message

Ian Lance Taylor Jan. 6, 2015, 6:57 p.m. UTC 
This patch by Chris Manghane skips initializing zero-sized fields in
constructor expressions.  Initializing them tends to lead into GIMPLE
errors when using map composite literals.  Note that zero-sized fields
are useful in maps, but of course the compiler should not crash.  This
is http://golang.org/issue/9406 .  Bootstrapped and ran Go testsuite
on x86_64-unknown-linux-gnu.  Committed to mainline.

Ian

2015-01-06  Chris Manghane  <cmang@google.com>

* go-gcc.cc (constructor_expression): Don't initialize zero-sized
fields, just evaluate the values for side effects.
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Patch

Index: go-gcc.cc
===================================================================
--- go-gcc.cc	(revision 219261)
+++ go-gcc.cc	(working copy)
@@ -1656,6 +1656,7 @@  Gcc_backend::constructor_expression(Btyp
   vec<constructor_elt, va_gc> *init;
   vec_alloc(init, vals.size());
 
+  tree sink = NULL_TREE;
   bool is_constant = true;
   tree field = TYPE_FIELDS(type_tree);
   for (std::vector<Bexpression*>::const_iterator p = vals.begin();
@@ -1669,6 +1670,17 @@  Gcc_backend::constructor_expression(Btyp
           || TREE_TYPE(val) == error_mark_node)
         return this->error_expression();
 
+      if (int_size_in_bytes(TREE_TYPE(field)) == 0)
+	{
+	  // GIMPLE cannot represent indices of zero-sized types so
+	  // trying to construct a map with zero-sized keys might lead
+	  // to errors.  Instead, we evaluate each expression that
+	  // would have been added as a map element for its
+	  // side-effects and construct an empty map.
+	  append_to_statement_list(val, &sink);
+	  continue;
+	}
+
       constructor_elt empty = {NULL, NULL};
       constructor_elt* elt = init->quick_push(empty);
       elt->index = field;
@@ -1681,7 +1693,9 @@  Gcc_backend::constructor_expression(Btyp
   tree ret = build_constructor(type_tree, init);
   if (is_constant)
     TREE_CONSTANT(ret) = 1;
-
+  if (sink != NULL_TREE)
+    ret = fold_build2_loc(location.gcc_location(), COMPOUND_EXPR,
+			  type_tree, sink, ret);
   return this->make_expression(ret);
 }