c++: constexpr bit_cast with empty field

The change to only cache constexpr calls that are
reduced_constant_expression_p tripped on bit-cast3.C, which failed that
predicate due to the presence of an empty field in the result of
native_interpret_aggregate, which reduced_constant_expression_p rejects to
avoid confusing output_constructor.

This patch proposes to skip such fields in native_interpret_aggregate, since
they aren't actually involved in the value representation.

gcc/ChangeLog:

	* fold-const.cc (native_interpret_aggregate): Skip empty fields.

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_bit_cast): Check that the result of
	native_interpret_aggregate doesn't need more evaluation.

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 9d85c3be5cc9b498aed0a0689cae6008225f4344..6e8f1c2b61ecaa1de1ba3f143ee4c6dc6a347f15 100644 (file)
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1440,6 +1440,8 @@ enum value_cat {
 
 static tree cxx_eval_constant_expression (const constexpr_ctx *, tree,
                                          value_cat, bool *, bool *, tree * = NULL);
+static tree cxx_eval_bare_aggregate (const constexpr_ctx *, tree,
+                                    value_cat, bool *, bool *);
 static tree cxx_fold_indirect_ref (const constexpr_ctx *, location_t, tree, tree,
                                   bool * = NULL);
 static tree find_heap_var_refs (tree *, int *, void *);
@@ -4803,6 +4805,13 @@ cxx_eval_bit_cast (const constexpr_ctx *ctx, tree t, bool *non_constant_p,
        {
          clear_type_padding_in_mask (TREE_TYPE (t), mask);
          clear_uchar_or_std_byte_in_mask (loc, r, mask);
+         if (CHECKING_P)
+           {
+             tree e = cxx_eval_bare_aggregate (ctx, r, vc_prvalue,
+                                               non_constant_p, overflow_p);
+             gcc_checking_assert (e == r);
+             r = e;
+           }
        }
     }
 

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index a02ede79fed28cc3cd3cc01ba9c6d8867a6a03e5..7e5494dfd392105ee3e28583ebede49b61580f7b 100644 (file)
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -8935,7 +8935,8 @@ native_interpret_aggregate (tree type, const unsigned char *ptr, int off,
     return NULL_TREE;
   for (tree field = TYPE_FIELDS (type); field; field = DECL_CHAIN (field))
     {
-      if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field))
+      if (TREE_CODE (field) != FIELD_DECL || DECL_PADDING_P (field)
+         || is_empty_type (TREE_TYPE (field)))
        continue;
       tree fld = field;
       HOST_WIDE_INT bitoff = 0, pos = 0, sz = 0;