On Mon, Jul 18, 2011 at 7:49 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> Hi!
>
> As the testcase below shows, fold_nonarray_ctor_reference doesn't have a
> correct check whether a field might overlap with the given offset, size
> access (in this case a BIT_FIELD_REF). The bitfield ref wants to read
> 8 bits starting at offset 0, the bitfield defined there goes from bit 1
> 1 bit and as fold_nonarray_ctor_reference doesn't detect an overlap,
> it says the result is 0 as if there was an initializer, but without any
> overlapping fields. Fixed thusly, bootstrapped/regtested on x86_64-linux
> and i686-linux, ok for trunk/4.6?
Ok.
Thanks,
Richard.
> For trunk I think we could eventually do better and handle even multiple
> fields overlapping the access and/or non-zero offsets within that,
> provided the recursive call to fold_ctor_reference returned an INTEGER_CST
> we could mask/shift/or them together.
>
> 2011-07-18 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/49768
> * gimple-fold.c (fold_nonarray_ctor_reference): Return NULL
> if offset is smaller than bitoffset, but offset+size is bigger
> than bitoffset.
>
> * gcc.c-torture/execute/pr49768.c: New test.
>
> --- gcc/gimple-fold.c.jj 2011-07-15 20:46:49.000000000 +0200
> +++ gcc/gimple-fold.c 2011-07-18 14:28:35.000000000 +0200
> @@ -3231,7 +3231,7 @@ fold_nonarray_ctor_reference (tree type,
> double_int bitoffset;
> double_int byte_offset_cst = tree_to_double_int (byte_offset);
> double_int bits_per_unit_cst = uhwi_to_double_int (BITS_PER_UNIT);
> - double_int bitoffset_end;
> + double_int bitoffset_end, access_end;
>
> /* Variable sized objects in static constructors makes no sense,
> but field_size can be NULL for flexible array members. */
> @@ -3252,14 +3252,16 @@ fold_nonarray_ctor_reference (tree type,
> else
> bitoffset_end = double_int_zero;
>
> - /* Is OFFSET in the range (BITOFFSET, BITOFFSET_END)? */
> - if (double_int_cmp (uhwi_to_double_int (offset), bitoffset, 0) >= 0
> + access_end = double_int_add (uhwi_to_double_int (offset),
> + uhwi_to_double_int (size));
> +
> + /* Is there any overlap between [OFFSET, OFFSET+SIZE) and
> + [BITOFFSET, BITOFFSET_END)? */
> + if (double_int_cmp (access_end, bitoffset, 0) > 0
> && (field_size == NULL_TREE
> || double_int_cmp (uhwi_to_double_int (offset),
> bitoffset_end, 0) < 0))
> {
> - double_int access_end = double_int_add (uhwi_to_double_int (offset),
> - uhwi_to_double_int (size));
> double_int inner_offset = double_int_sub (uhwi_to_double_int
> (offset),
> bitoffset);
> /* We do have overlap. Now see if field is large enough to
> @@ -3267,6 +3269,8 @@ fold_nonarray_ctor_reference (tree type,
> fields. */
> if (double_int_cmp (access_end, bitoffset_end, 0) > 0)
> return NULL_TREE;
> + if (double_int_cmp (uhwi_to_double_int (offset), bitoffset, 0) < 0)
> + return NULL_TREE;
> return fold_ctor_reference (type, cval,
> double_int_to_uhwi (inner_offset), size);
> }
> --- gcc/testsuite/gcc.c-torture/execute/pr49768.c.jj 2011-07-18
> 14:37:18.000000000 +0200
> +++ gcc/testsuite/gcc.c-torture/execute/pr49768.c 2011-07-18
> 14:37:03.000000000 +0200
> @@ -0,0 +1,12 @@
> +/* PR tree-optimization/49768 */
> +
> +extern void abort (void);
> +
> +int
> +main ()
> +{
> + static struct { unsigned int : 1; unsigned int s : 1; } s = { .s = 1 };
> + if (s.s != 1)
> + abort ();
> + return 0;
> +}
>
> Jakub
>
