On Wed, Dec 4, 2013 at 1:03 AM, Richard Sandiford
<rdsandif...@googlemail.com> wrote:
> Richard Biener <richard.guent...@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) \
