On Wed, 9 Dec 2020, Jakub Jelinek wrote:
> Hi!
>
> With the bit_cast changes, I have added support for bitfields which don't
> have scalar representatives. For bit_cast it works fine, as when mask
> is non-NULL, off is asserted to be 0. But when native_encode_initializer
> is called e.g. from sccvn with off > 0 (i.e. we are interested in encoding
> just a few bytes out of it somewhere from the middle or at the end), the
> following computations are incorrect.
> pos is a byte position from the start of the constructor, repr_size is the
> size in bytes of the bit-field representative and len is the length
> of the buffer. If the buffer is offsetted by positive off, those numbers
> are uncomparable though, we need to add off to len to make both
> count bytes from the start of the constructor, and o is a utility temporary
> set to off != -1 ? off : 0 (because off -1 also means start at offset 0
> and just force special behavior).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2020-12-09 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/98199
> * fold-const.c (native_encode_initializer): Fix handling bit-fields
> when off > 0.
>
> * gcc.c-torture/compile/pr98199.c: New test.
>
> --- gcc/fold-const.c.jj 2020-12-08 12:42:53.000000000 +0100
> +++ gcc/fold-const.c 2020-12-08 15:26:43.055445045 +0100
> @@ -8320,11 +8320,11 @@ native_encode_initializer (tree init, un
> return 0;
> HOST_WIDE_INT repr_size = int_size_in_bytes (repr_type);
> gcc_assert (repr_size > 0 && repr_size <= len);
> - if (pos + repr_size <= len)
> + if (pos + repr_size <= o + len)
> rpos = pos;
> else
> {
> - rpos = len - repr_size;
> + rpos = o + len - repr_size;
> gcc_assert (rpos <= pos);
> }
> }
> --- gcc/testsuite/gcc.c-torture/compile/pr98199.c.jj 2020-12-08
> 15:37:15.082465022 +0100
> +++ gcc/testsuite/gcc.c-torture/compile/pr98199.c 2020-12-08
> 15:36:51.032730617 +0100
> @@ -0,0 +1,7 @@
> +/* PR tree-optimization/98199 */
> +
> +struct A { long a; short d; int c, f, e, g; };
> +struct B { int a, i; short j; struct A k; signed : 20; int e, g; }
> __attribute__((packed));
> +struct C { short a; unsigned i, k; struct B d; const int : 30; signed e :
> 20; signed : 18; };
> +const struct C l = { 1, 6, 0, {}, 0 };
> +int foo (void) { return l.e || 0; }
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
