On Sat, 18 Jul 2020, Jakub Jelinek wrote:
> Hi!
>
> When working on __builtin_bit_cast that needs to handle bitfields too,
> I've made the following change to handle at least some bitfields in
> fold_const_aggregate_ref_1 (those that have integral representative).
> It already handles some, but only those that start and end at byte
> boundaries.
>
> Bootstrapped/regtested on {x86_64,i686,powerpc64{,le}}-linux, ok for trunk?
OK.
Richard.
> 2020-07-18 Jakub Jelinek <ja...@redhat.com>
>
> PR libstdc++/93121
> * gimple-fold.c (fold_const_aggregate_ref_1): For COMPONENT_REF
> of a bitfield not aligned on byte boundaries try to
> fold_ctor_reference DECL_BIT_FIELD_REPRESENTATIVE if any and
> adjust it depending on endianity.
>
> * gcc.dg/tree-ssa/pr93121-2.c: New test.
>
> --- gcc/gimple-fold.c.jj 2020-07-13 19:09:33.218871556 +0200
> +++ gcc/gimple-fold.c 2020-07-17 19:17:59.694537680 +0200
> @@ -7189,8 +7189,64 @@ fold_const_aggregate_ref_1 (tree t, tree
> if (maybe_lt (offset, 0))
> return NULL_TREE;
>
> - return fold_ctor_reference (TREE_TYPE (t), ctor, offset, size,
> - base);
> + tem = fold_ctor_reference (TREE_TYPE (t), ctor, offset, size, base);
> + if (tem)
> + return tem;
> +
> + /* For bit field reads try to read the representative and
> + adjust. */
> + if (TREE_CODE (t) == COMPONENT_REF
> + && DECL_BIT_FIELD (TREE_OPERAND (t, 1))
> + && DECL_BIT_FIELD_REPRESENTATIVE (TREE_OPERAND (t, 1)))
> + {
> + HOST_WIDE_INT csize, coffset;
> + tree field = TREE_OPERAND (t, 1);
> + tree repr = DECL_BIT_FIELD_REPRESENTATIVE (field);
> + if (INTEGRAL_TYPE_P (TREE_TYPE (repr))
> + && size.is_constant (&csize)
> + && offset.is_constant (&coffset)
> + && (coffset % BITS_PER_UNIT != 0
> + || csize % BITS_PER_UNIT != 0)
> + && !reverse
> + && BYTES_BIG_ENDIAN == WORDS_BIG_ENDIAN)
> + {
> + poly_int64 bitoffset;
> + poly_uint64 field_offset, repr_offset;
> + if (poly_int_tree_p (DECL_FIELD_OFFSET (field), &field_offset)
> + && poly_int_tree_p (DECL_FIELD_OFFSET (repr), &repr_offset))
> + bitoffset = (field_offset - repr_offset) * BITS_PER_UNIT;
> + else
> + bitoffset = 0;
> + bitoffset += (tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field))
> + - tree_to_uhwi (DECL_FIELD_BIT_OFFSET (repr)));
> + HOST_WIDE_INT bitoff;
> + int diff = (TYPE_PRECISION (TREE_TYPE (repr))
> + - TYPE_PRECISION (TREE_TYPE (field)));
> + if (bitoffset.is_constant (&bitoff)
> + && bitoff >= 0
> + && bitoff <= diff)
> + {
> + offset -= bitoff;
> + size = tree_to_uhwi (DECL_SIZE (repr));
> +
> + tem = fold_ctor_reference (TREE_TYPE (repr), ctor, offset,
> + size, base);
> + if (tem && TREE_CODE (tem) == INTEGER_CST)
> + {
> + if (!BYTES_BIG_ENDIAN)
> + tem = wide_int_to_tree (TREE_TYPE (field),
> + wi::lrshift (wi::to_wide (tem),
> + bitoff));
> + else
> + tem = wide_int_to_tree (TREE_TYPE (field),
> + wi::lrshift (wi::to_wide (tem),
> + diff - bitoff));
> + return tem;
> + }
> + }
> + }
> + }
> + break;
>
> case REALPART_EXPR:
> case IMAGPART_EXPR:
> --- gcc/testsuite/gcc.dg/tree-ssa/pr93121-2.c.jj 2020-07-17
> 19:47:31.842426096 +0200
> +++ gcc/testsuite/gcc.dg/tree-ssa/pr93121-2.c 2020-07-17 19:48:24.551649910
> +0200
> @@ -0,0 +1,22 @@
> +/* PR libstdc++/93121 */
> +/* { dg-do compile { target { ilp32 || lp64 } } } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +union U { int a[3]; struct S { int d; int a : 3; int b : 24; int c : 5; int
> e; } b; };
> +const union U u = { .a = { 0x7efa3412, 0x5a876543, 0x1eeffeed } };
> +int a, b, c;
> +
> +void
> +foo ()
> +{
> + a = u.b.a;
> + b = u.b.b;
> + c = u.b.c;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "a = 3;" 1 "optimized" { target le } }
> } */
> +/* { dg-final { scan-tree-dump-times "b = 5303464;" 1 "optimized" { target
> le } } } */
> +/* { dg-final { scan-tree-dump-times "c = 11;" 1 "optimized" { target le } }
> } */
> +/* { dg-final { scan-tree-dump-times "a = 2;" 1 "optimized" { target be } }
> } */
> +/* { dg-final { scan-tree-dump-times "b = -2868438;" 1 "optimized" { target
> be } } } */
> +/* { dg-final { scan-tree-dump-times "c = 3;" 1 "optimized" { target be } }
> } */
>
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
