vla: evaluate operand of sizeof if its type is a vla

The c99 standard in "6.5.3.4 The sizeof operator" states:

 If the type of the operand is a variable length array type, the operand
 is evaluated;[...]

This patch mirrors the following c99 semantic in gdb:

 1| int vla[n][m];
 2| int i = 1;
 3| sizeof(vla[i++][0]); // No sideffect
 4| assert (i == 1);
 5| sizeof(vla[i++]);    // With sideffect
 6| assert (i == 2);

Note: ptype/whatis still do not allow any sideeffects.

This patch was motivated by:

  https://sourceware.org/ml/gdb-patches/2014-01/msg00732.html

gdb/ChangeLog:

	* eval.c (evaluate_subexp_for_sizeof): Add enum noside argument.
	(evaluate_subexp_standard): Pass noside argument.
	(evaluate_subexp_for_sizeof) <BINOP_SUBSCRIPT>: Handle subscript case
	if noside equals EVAL_NORMAL. If the subscript yields a vla type
	re-evaluate subscript operation with EVAL_NORMAL to enable sideffects.
	* gdbtypes.c (resolve_dynamic_bounds): Mark bound as evaluated.
	* gdbtypes.h (enum range_flags): Add RANGE_EVALUATED case.

testsuite/ChangeLog:

	* gdb.base/vla-sideeffect.c: New file.
	* gdb.base/vla-sideeffect.exp: New file.

1 files changed, 39 insertions, 4 deletions

diff --git a/gdb/eval.c b/gdb/eval.c
index 22392eb..3e62ead 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -50,7 +50,8 @@ extern int overload_resolution;
 
 /* Prototypes for local functions.  */
 
-static struct value *evaluate_subexp_for_sizeof (struct expression *, int *);
+static struct value *evaluate_subexp_for_sizeof (struct expression *, int *,
+						 enum noside);
 
 static struct value *evaluate_subexp_for_address (struct expression *,
 						  int *, enum noside);
@@ -2562,7 +2563,7 @@ evaluate_subexp_standard (struct type *expect_type,
 	  evaluate_subexp (NULL_TYPE, exp, pos, EVAL_SKIP);
 	  goto nosideret;
 	}
-      return evaluate_subexp_for_sizeof (exp, pos);
+      return evaluate_subexp_for_sizeof (exp, pos, noside);
 
     case UNOP_CAST:
       (*pos) += 2;
@@ -2996,10 +2997,13 @@ evaluate_subexp_with_coercion (struct expression *exp,
 
 /* Evaluate a subexpression of EXP, at index *POS,
    and return a value for the size of that subexpression.
-   Advance *POS over the subexpression.  */
+   Advance *POS over the subexpression.  If NOSIDE is EVAL_NORMAL
+   we allow side-effects on the operand if its type is a variable
+   length array.   */
 
 static struct value *
-evaluate_subexp_for_sizeof (struct expression *exp, int *pos)
+evaluate_subexp_for_sizeof (struct expression *exp, int *pos,
+			    enum noside noside)
 {
   /* FIXME: This should be size_t.  */
   struct type *size_type = builtin_type (exp->gdbarch)->builtin_int;
@@ -3052,6 +3056,37 @@ evaluate_subexp_for_sizeof (struct expression *exp, int *pos)
 	(*pos) += 4;
       break;
 
+      /* Deal with the special case if NOSIDE is EVAL_NORMAL and the resulting
+	 type of the subscript is a variable length array type. In this case we
+	 must re-evaluate the right hand side of the subcription to allow
+	 side-effects. */
+    case BINOP_SUBSCRIPT:
+      if (noside == EVAL_NORMAL)
+	{
+	  int pc = (*pos) + 1;
+
+	  val = evaluate_subexp (NULL_TYPE, exp, &pc, EVAL_AVOID_SIDE_EFFECTS);
+	  type = check_typedef (value_type (val));
+	  if (TYPE_CODE (type) == TYPE_CODE_ARRAY)
+	    {
+	      type = check_typedef (TYPE_TARGET_TYPE (type));
+	      if (TYPE_CODE (type) == TYPE_CODE_ARRAY)
+		{
+		  type = TYPE_INDEX_TYPE (type);
+		  /* Only re-evaluate the right hand side if the resulting type
+		     is a variable length type.  */
+		  if (TYPE_RANGE_DATA (type)->flag_bound_evaluated)
+		    {
+		      val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_NORMAL);
+		      return value_from_longest
+			(size_type, (LONGEST) TYPE_LENGTH (value_type (val)));
+		    }
+		}
+	    }
+	}
+
+      /* Fall through.  */
+
     default:
       val = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_AVOID_SIDE_EFFECTS);
       type = value_type (val);