On Thu, 26 Nov 2020, Jakub Jelinek wrote:
> Hi!
>
> When playing with __builtin_bit_cast, I have noticed __builtin_clear_padding
> ICE on the G class below. The artificial field with D type has offset 0
> and size 8 bytes, but the following artificial field with E type has offset
> 0 and size 0, so it triggers the asserts that we don't move current position
> backwards. Fixed by ignoring is_empty_type (TREE_TYPE (field)) fields, all
> of their bits are padding which is what is added when skipping over to next
> field anyway.
>
> Ok for trunk if it passes bootstrap/regtest? So far passed all
> builtin-clear-padding* tests, so everything that uses these functions ATM
> in the GCC tree.
OK.
Richard.
> 2020-11-26 Jakub Jelinek <ja...@redhat.com>
>
> PR libstdc++/88101
> * gimple-fold.c (clear_padding_type): Ignore fields with is_empty_type
> types.
>
> * g++.dg/torture/builtin-clear-padding-3.C: New test.
>
> --- gcc/gimple-fold.c.jj 2020-11-26 14:05:07.393268700 +0100
> +++ gcc/gimple-fold.c 2020-11-26 14:18:10.826532574 +0100
> @@ -4533,6 +4533,8 @@ clear_padding_type (clear_padding_struct
> "well defined padding bits for %qs",
> field, "__builtin_clear_padding");
> }
> + else if (is_empty_type (TREE_TYPE (field)))
> + continue;
> else
> {
> HOST_WIDE_INT pos = int_byte_position (field);
> --- gcc/testsuite/g++.dg/torture/builtin-clear-padding-3.C.jj 2020-11-26
> 14:26:40.532848182 +0100
> +++ gcc/testsuite/g++.dg/torture/builtin-clear-padding-3.C 2020-11-26
> 14:27:51.995051122 +0100
> @@ -0,0 +1,24 @@
> +/* PR libstdc++/88101 */
> +
> +struct D { int a; int : 24; int b : 8; };
> +struct E {};
> +struct F { char c, d, e; };
> +struct G : public D, E, F { int f; } g1, g2;
> +
> +__attribute__((noipa)) void
> +foo (G *g)
> +{
> + g->a = -1; g->b = -1; g->c = -1; g->d = -1; g->e = -1; g->f = -1;
> +}
> +
> +int
> +main ()
> +{
> + __builtin_memset (&g2, -1, sizeof (g2));
> + foo (&g1);
> + foo (&g2);
> + __builtin_clear_padding (&g2);
> + if (__builtin_memcmp (&g1, &g2, sizeof (g1)))
> + __builtin_abort ();
> + return 0;
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imend
