Re: Add TREE_INT_CST_OFFSET_NUNITS

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Dec 4, 2013 at 1:03 AM, Richard Sandiford
<rdsandiford@googlemail.com> wrote:
> Richard Biener <richard.guenther@gmail.com> writes:
>>>> Looking at the implementation it seems it would also work with
>>>>
>>>>    return MIN (TREE_INT_CST_EXT_NUNITS (m_t), N / HOST_BITS_PER_WIDE_INT);
>>>
>>> Yeah, the MIN in the patch was probably bogus sorry.  It only works
>>> if we can assume that no bitsizetype will have ADDR_MAX_PRECISION
>>> significant (non-sign) bits -- in particular that there's no such thing as
>>> an all-1s _unsigned_ bitsizetype.  That might be true in practice given
>>> the way we use offsets, but it isn't safe to generalise that to all N.
>>>
>>> A safer form would be:
>>>
>>>    if (ext_len > OFFSET_INT_ELTS)
>>>      TREE_INT_CST_OFFSET_NUNITS (t) = len;
>>>    else
>>>      TREE_INT_CST_OFFSET_NUNITS (t) = ext_len;
>>>
>>> The reason the general form doesn't work for all N is because of the
>>> compressed representation.  E.g. the example I gave a while ago about
>>> a 256-bit all-1s unsigned number being { -1 } as a 256-bit number and
>>> { -1, -1, -1, -1, 0 } as a 257+-bit number.
>>>
>>> But the point of the patch is to avoid any runtime checks here,
>>> so the TYPE_PRECISION case is never actually used now.  I just kept
>>> it around for completeness, since we'd been using it successfully so far.
>>> I can put in a gcc_unreachable if you prefer.
>>
>> Yeah, I'd prefer a gcc_unreachable and a comment.
>
> OK, how about this version?  Tested on x86_64-linux-gnu.

Ok.

Thanks,
Richard.

> Thanks,
> Richard
>
>
> Index: gcc/ChangeLog.wide-int
> ===================================================================
> --- gcc/ChangeLog.wide-int      2013-12-03 23:55:26.142873345 +0000
> +++ gcc/ChangeLog.wide-int      2013-12-03 23:59:18.823744425 +0000
> @@ -617,6 +617,7 @@
>         (TREE_INT_CST_HIGH): Delete.
>         (TREE_INT_CST_NUNITS): New.
>         (TREE_INT_CST_EXT_NUNITS): Likewise.
> +       (TREE_INT_CST_OFFSET_NUNITS): Likewise.
>         (TREE_INT_CST_ELT): Likewise.
>         (INT_CST_LT): Use wide-int interfaces.
>         (INT_CST_LE): New.
> Index: gcc/tree-core.h
> ===================================================================
> --- gcc/tree-core.h     2013-12-03 23:55:26.142873345 +0000
> +++ gcc/tree-core.h     2013-12-04 00:02:22.910222722 +0000
> @@ -764,11 +764,17 @@ struct GTY(()) tree_base {
>      struct {
>        /* The number of HOST_WIDE_INTs if the INTEGER_CST is accessed in
>          its native precision.  */
> -      unsigned short unextended;
> +      unsigned char unextended;
>
>        /* The number of HOST_WIDE_INTs if the INTEGER_CST is extended to
>          wider precisions based on its TYPE_SIGN.  */
> -      unsigned short extended;
> +      unsigned char extended;
> +
> +      /* The number of HOST_WIDE_INTs if the INTEGER_CST is accessed in
> +        offset_int precision, with smaller integers being extended
> +        according to their TYPE_SIGN.  This is equal to one of the two
> +        fields above but is cached for speed.  */
> +      unsigned char offset;
>      } int_length;
>
>      /* VEC length.  This field is only used with TREE_VEC.  */
> Index: gcc/tree.c
> ===================================================================
> --- gcc/tree.c  2013-12-03 23:55:26.142873345 +0000
> +++ gcc/tree.c  2013-12-03 23:59:18.821744409 +0000
> @@ -1285,6 +1285,7 @@ wide_int_to_tree (tree type, const wide_
>             /* Make sure no one is clobbering the shared constant.  */
>             gcc_checking_assert (TREE_TYPE (t) == type
>                                  && TREE_INT_CST_NUNITS (t) == 1
> +                                && TREE_INT_CST_OFFSET_NUNITS (t) == 1
>                                  && TREE_INT_CST_EXT_NUNITS (t) == 1
>                                  && TREE_INT_CST_ELT (t, 0) == hwi);
>           else
> @@ -1964,6 +1965,13 @@ make_int_cst_stat (int len, int ext_len
>    TREE_SET_CODE (t, INTEGER_CST);
>    TREE_INT_CST_NUNITS (t) = len;
>    TREE_INT_CST_EXT_NUNITS (t) = ext_len;
> +  /* to_offset can only be applied to trees that are offset_int-sized
> +     or smaller.  EXT_LEN is correct if it fits, otherwise the constant
> +     must be exactly the precision of offset_int and so LEN is correct.  */
> +  if (ext_len <= OFFSET_INT_ELTS)
> +    TREE_INT_CST_OFFSET_NUNITS (t) = ext_len;
> +  else
> +    TREE_INT_CST_OFFSET_NUNITS (t) = len;
>
>    TREE_CONSTANT (t) = 1;
>
> Index: gcc/tree.h
> ===================================================================
> --- gcc/tree.h  2013-12-03 23:55:26.142873345 +0000
> +++ gcc/tree.h  2013-12-04 00:01:48.258944485 +0000
> @@ -907,6 +907,8 @@ #define TREE_INT_CST_NUNITS(NODE) \
>    (INTEGER_CST_CHECK (NODE)->base.u.int_length.unextended)
>  #define TREE_INT_CST_EXT_NUNITS(NODE) \
>    (INTEGER_CST_CHECK (NODE)->base.u.int_length.extended)
> +#define TREE_INT_CST_OFFSET_NUNITS(NODE) \
> +  (INTEGER_CST_CHECK (NODE)->base.u.int_length.offset)
>  #define TREE_INT_CST_ELT(NODE, I) TREE_INT_CST_ELT_CHECK (NODE, I)
>  #define TREE_INT_CST_LOW(NODE) \
>    ((unsigned HOST_WIDE_INT) TREE_INT_CST_ELT (NODE, 0))
> @@ -4623,11 +4625,15 @@ wi::extended_tree <N>::get_val () const
>  inline unsigned int
>  wi::extended_tree <N>::get_len () const
>  {
> -  if (N == MAX_BITSIZE_MODE_ANY_INT
> -      || N > TYPE_PRECISION (TREE_TYPE (m_t)))
> +  if (N == ADDR_MAX_PRECISION)
> +    return TREE_INT_CST_OFFSET_NUNITS (m_t);
> +  else if (N == MAX_BITSIZE_MODE_ANY_INT)
>      return TREE_INT_CST_EXT_NUNITS (m_t);
>    else
> -    return TREE_INT_CST_NUNITS (m_t);
> +    /* This class is designed to be used for specific output precisions
> +       and needs to be as fast as possible, so there is no fallback for
> +       other casees.  */
> +    gcc_unreachable ();
>  }
>
>  namespace wi
> Index: gcc/wide-int.h
> ===================================================================
> --- gcc/wide-int.h      2013-12-03 23:59:08.135658583 +0000
> +++ gcc/wide-int.h      2013-12-03 23:59:18.823744425 +0000
> @@ -256,6 +256,9 @@ #define ADDR_MAX_BITSIZE 64
>  #define ADDR_MAX_PRECISION \
>    ((ADDR_MAX_BITSIZE + 4 + HOST_BITS_PER_WIDE_INT - 1) & ~(HOST_BITS_PER_WIDE_INT - 1))
>
> +/* The number of HWIs needed to store an offset_int.  */
> +#define OFFSET_INT_ELTS (ADDR_MAX_PRECISION / HOST_BITS_PER_WIDE_INT)
> +
>  /* The type of result produced by a binary operation on types T1 and T2.
>     Defined purely for brevity.  */
>  #define WI_BINARY_RESULT(T1, T2) \