Handle alignof and _Alignof

This adds alignof and _Alignof to the C/C++ expression parser, and
adds new tests to test the features.  The tests are written to try to
ensure that gdb's knowledge of alignment rules stays in sync with the
compiler's.

2018-04-30  Tom Tromey  <tom@tromey.com>

	PR exp/17095:
	* NEWS: Update.
	* std-operator.def (UNOP_ALIGNOF): New operator.
	* expprint.c (dump_subexp_body_standard) <case UNOP_ALIGNOF>:
	New.
	* eval.c (evaluate_subexp_standard) <case UNOP_ALIGNOF>: New.
	* c-lang.c (c_op_print_tab): Add alignof.
	* c-exp.y (ALIGNOF): New token.
	(exp): Add "ALIGNOF" production.
	(ident_tokens): Add _Alignof and alignof.

2018-04-30  Tom Tromey  <tom@tromey.com>

	PR exp/17095:
	* gdb.dwarf2/dw2-align.exp: New file.
	* gdb.cp/align.exp: New file.
	* gdb.base/align.exp: New file.
	* lib/gdb.exp (gdb_int128_helper): New proc.
	(has_int128_c, has_int128_cxx): New caching procs.

1 files changed, 13 insertions, 0 deletions

diff --git a/gdb/eval.c b/gdb/eval.c
index ad66f7c..2fdfdf9 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -2667,6 +2667,19 @@ evaluate_subexp_standard (struct type *expect_type,
 	}
       return evaluate_subexp_for_sizeof (exp, pos, noside);
 
+    case UNOP_ALIGNOF:
+      {
+	struct type *type
+	  = value_type (evaluate_subexp (NULL_TYPE, exp, pos,
+					 EVAL_AVOID_SIDE_EFFECTS));
+	/* FIXME: This should be size_t.  */
+	struct type *size_type = builtin_type (exp->gdbarch)->builtin_int;
+	ULONGEST align = type_align (type);
+	if (align == 0)
+	  error (_("could not determine alignment of type"));
+	return value_from_longest (size_type, align);
+      }
+
     case UNOP_CAST:
       (*pos) += 2;
       type = exp->elts[pc + 1].type;