Kenneth Zadeck <zad...@naturalbridge.com> writes:
> like the add/sub patch, enhance the comment so that it says that it is
> designed to hit the widestint and offset int common cases.
These cases are designed for all types, not just offset_int and widest_int.
We're using length-based tests because that catches more cases for all types.
The add/sub case is different because I'm keeping the existing
precision-based fast path for wide_int and adding a new fast path
for offset_int and widest_int.
Thanks,
Richard
> kenny
> On 11/28/2013 12:34 PM, Richard Sandiford wrote:
>> As Richi asked, this patch makes cmps use the same shortcuts as lts_p.
>> It also makes cmpu use the shortcut that I justed added to ltu_p.
>>
>> On that same fold-const.ii testcase, this reduces the number of cmps_large
>> calls from 66924 to 916. It reduces the number of cmpu_large calls from
>> 3462 to 4.
>>
>> Tested on x86_64-linux-gnu. OK to install?
>>
>> Thanks,
>> Richard
>>
>>
>> Index: gcc/wide-int.h
>> ===================================================================
>> --- gcc/wide-int.h 2001-01-01 00:00:00.000000000 +0000
>> +++ gcc/wide-int.h 2013-11-28 16:08:22.527681077 +0000
>> @@ -1858,17 +1858,31 @@ wi::cmps (const T1 &x, const T2 &y)
>> unsigned int precision = get_binary_precision (x, y);
>> WIDE_INT_REF_FOR (T1) xi (x, precision);
>> WIDE_INT_REF_FOR (T2) yi (y, precision);
>> - if (precision <= HOST_BITS_PER_WIDE_INT)
>> + if (wi::fits_shwi_p (yi))
>> {
>> - HOST_WIDE_INT xl = xi.to_shwi ();
>> - HOST_WIDE_INT yl = yi.to_shwi ();
>> - if (xl < yl)
>> + /* Special case for comparisons with 0. */
>> + if (STATIC_CONSTANT_P (yi.val[0] == 0))
>> + return neg_p (xi) ? -1 : !(xi.len == 1 && xi.val[0] == 0);
>> + /* If x fits into a signed HWI, we can compare directly. */
>> + if (wi::fits_shwi_p (xi))
>> + {
>> + HOST_WIDE_INT xl = xi.to_shwi ();
>> + HOST_WIDE_INT yl = yi.to_shwi ();
>> + return xl < yl ? -1 : xl > yl;
>> + }
>> + /* If x doesn't fit and is negative, then it must be more
>> + negative than any signed HWI, and hence smaller than y. */
>> + if (neg_p (xi))
>> return -1;
>> - else if (xl > yl)
>> - return 1;
>> - else
>> - return 0;
>> + /* If x is positive, then it must be larger than any signed HWI,
>> + and hence greater than y. */
>> + return 1;
>> }
>> + /* Optimize the opposite case, if it can be detected at compile time. */
>> + if (STATIC_CONSTANT_P (xi.len == 1))
>> + /* If YI is negative it is lower than the least HWI.
>> + If YI is positive it is greater than the greatest HWI. */
>> + return neg_p (yi) ? 1 : -1;
>> return cmps_large (xi.val, xi.len, precision, yi.val, yi.len);
>> }
>>
>> @@ -1881,16 +1895,35 @@ wi::cmpu (const T1 &x, const T2 &y)
>> unsigned int precision = get_binary_precision (x, y);
>> WIDE_INT_REF_FOR (T1) xi (x, precision);
>> WIDE_INT_REF_FOR (T2) yi (y, precision);
>> - if (precision <= HOST_BITS_PER_WIDE_INT)
>> + /* Optimize comparisons with constants. */
>> + if (STATIC_CONSTANT_P (yi.len == 1 && yi.val[0] >= 0))
>> {
>> + /* If XI doesn't fit in a HWI then it must be larger than YI. */
>> + if (xi.len != 1)
>> + return 1;
>> + /* Otherwise compare directly. */
>> unsigned HOST_WIDE_INT xl = xi.to_uhwi ();
>> - unsigned HOST_WIDE_INT yl = yi.to_uhwi ();
>> - if (xl < yl)
>> + unsigned HOST_WIDE_INT yl = yi.val[0];
>> + return xl < yl ? -1 : xl > yl;
>> + }
>> + if (STATIC_CONSTANT_P (xi.len == 1 && xi.val[0] >= 0))
>> + {
>> + /* If YI doesn't fit in a HWI then it must be larger than XI. */
>> + if (yi.len != 1)
>> return -1;
>> - else if (xl == yl)
>> - return 0;
>> - else
>> - return 1;
>> + /* Otherwise compare directly. */
>> + unsigned HOST_WIDE_INT xl = xi.val[0];
>> + unsigned HOST_WIDE_INT yl = yi.to_uhwi ();
>> + return xl < yl ? -1 : xl > yl;
>> + }
>> + /* Optimize the case of two HWIs. The HWIs are implicitly sign-extended
>> + for precisions greater than HOST_BITS_WIDE_INT, but sign-extending both
>> + values does not change the result. */
>> + if (xi.len + yi.len == 2)
>> + {
>> + unsigned HOST_WIDE_INT xl = xi.to_uhwi ();
>> + unsigned HOST_WIDE_INT yl = yi.to_uhwi ();
>> + return xl < yl ? -1 : xl > yl;
>> }
>> return cmpu_large (xi.val, xi.len, precision, yi.val, yi.len);
>> }
>>
