Hi!
When native_encode_initializer is called with non-NULL mask (i.e. ATM
bit_cast only), it checks if the current index in the CONSTRUCTOR (if any)
is the next initializable FIELD_DECL, and if not, decrements cnt and
performs the iteration with that FIELD_DECL as field and val of zero
(so that it computes mask properly). As the testcase shows, I forgot to
set pos to the byte position of the field though (like it is done
for e.g. index referenced FIELD_DECLs in the constructor.
Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?
2020-12-09 Jakub Jelinek <ja...@redhat.com>
PR c++/98193
* fold-const.c (native_encode_initializer): Set pos to field's
byte position if iterating over a field with missing initializer.
* g++.dg/cpp2a/bit-cast7.C: New test.
--- gcc/fold-const.c.jj 2020-12-04 18:00:47.000000000 +0100
+++ gcc/fold-const.c 2020-12-08 12:42:53.913529423 +0100
@@ -8256,6 +8256,7 @@ native_encode_initializer (tree init, un
{
cnt--;
field = fld;
+ pos = int_byte_position (field);
val = build_zero_cst (TREE_TYPE (fld));
if (TREE_CODE (val) == CONSTRUCTOR)
to_free = val;
--- gcc/testsuite/g++.dg/cpp2a/bit-cast7.C.jj 2020-12-08 13:08:39.623341446
+0100
+++ gcc/testsuite/g++.dg/cpp2a/bit-cast7.C 2020-12-08 13:07:45.443943866
+0100
@@ -0,0 +1,39 @@
+// PR c++/98193
+// { dg-do compile { target c++20 } }
+
+template <typename To, typename From>
+constexpr To
+bit_cast (const From &from)
+{
+ return __builtin_bit_cast (To, from);
+}
+
+struct J
+{
+ long int a, b : 11, h;
+};
+
+struct K
+{
+ long int a, b : 11, c;
+ constexpr bool operator == (const K &x)
+ {
+ return a == x.a && b == x.b && c == x.c;
+ }
+};
+
+struct L
+{
+ long long int a, b : 11, h;
+};
+struct M
+{
+ long long int a, b : 11, c;
+ constexpr bool operator == (const M &x)
+ {
+ return a == x.a && b == x.b && c == x.c;
+ }
+};
+
+static_assert (bit_cast <K> (J{}) == K{}, "");
+static_assert (bit_cast <M> (L{0x0feedbacdeadbeefLL}) ==
M{0x0feedbacdeadbeefLL}, "");
Jakub
