On Wed, 9 Dec 2020, Jakub Jelinek wrote:
> 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?
OK.
Richard.
> 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
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
