On 12/07/2017 07:46 AM, Richard Biener wrote:
> On Wed, Dec 6, 2017 at 9:11 PM, Jeff Law <l...@redhat.com> wrote:
>> On 11/13/2017 05:04 PM, Richard Sandiford wrote:
>>> Richard Sandiford <richard.sandif...@linaro.org> writes:
>>>> Richard Sandiford <richard.sandif...@linaro.org> writes:
>>>>> This patch adds a new "poly_int" class to represent polynomial integers
>>>>> of the form:
>>>>>
>>>>> C0 + C1*X1 + C2*X2 ... + Cn*Xn
>>>>>
>>>>> It also adds poly_int-based typedefs for offsets and sizes of various
>>>>> precisions. In these typedefs, the Ci coefficients are compile-time
>>>>> constants and the Xi indeterminates are run-time invariants. The number
>>>>> of coefficients is controlled by the target and is initially 1 for all
>>>>> ports.
>>>>>
>>>>> Most routines can handle general coefficient counts, but for now a few
>>>>> are specific to one or two coefficients. Support for other coefficient
>>>>> counts can be added when needed.
>>>>>
>>>>> The patch also adds a new macro, IN_TARGET_CODE, that can be
>>>>> set to indicate that a TU contains target-specific rather than
>>>>> target-independent code. When this macro is set and the number of
>>>>> coefficients is 1, the poly-int.h classes define a conversion operator
>>>>> to a constant. This allows most existing target code to work without
>>>>> modification. The main exceptions are:
>>>>>
>>>>> - values passed through ..., which need an explicit conversion to a
>>>>> constant
>>>>>
>>>>> - ?: expression in which one arm ends up being a polynomial and the
>>>>> other remains a constant. In these cases it would be valid to convert
>>>>> the constant to a polynomial and the polynomial to a constant, so a
>>>>> cast is needed to break the ambiguity.
>>>>>
>>>>> The patch also adds a new target hook to return the estimated
>>>>> value of a polynomial for costing purposes.
>>>>>
>>>>> The patch also adds operator<< on wide_ints (it was already defined
>>>>> for offset_int and widest_int). I think this was originally excluded
>>>>> because >> is ambiguous for wide_int, but << is useful for converting
>>>>> bytes to bits, etc., so is worth defining on its own. The patch also
>>>>> adds operator% and operator/ for offset_int and widest_int, since those
>>>>> types are always signed. These changes allow the poly_int interface to
>>>>> be more predictable.
>>>>>
>>>>> I'd originally tried adding the tests as selftests, but that ended up
>>>>> bloating cc1 by at least a third. It also took a while to build them
>>>>> at -O2. The patch therefore uses plugin tests instead, where we can
>>>>> force the tests to be built at -O0. They still run in negligible time
>>>>> when built that way.
>>>>
>>>> Changes in v2:
>>>>
>>>> - Drop the controversial known_zero etc. wrapper functions.
>>>> - Fix the operator<<= bug that Martin found.
>>>> - Switch from "t" to "type" in SFINAE classes (requested by Martin).
>>>>
>>>> Not changed in v2:
>>>>
>>>> - Default constructors are still empty. I agree it makes sense to use
>>>> "= default" when we switch to C++11, but it would be dangerous for
>>>> that to make "poly_int64 x;" less defined than it is now.
>>>
>>> After talking about this a bit more internally, it was obvious that
>>> the choice of "must" and "may" for the predicate names was a common
>>> sticking point. The idea was to match the names of alias predicates,
>>> but given my track record with names ("too_empty_p" being a recently
>>> questioned example :-)), I'd be happy to rename them to something else.
>>> Some alternatives we came up with were:
>> I didn't find the must vs may naming problematical as I was going
>> through the changes. What I did find much more difficult was
>> determining if the behavior was correct when we used a "may" predicate.
>> It really relies a good deal on knowing the surrounding code.
>>
>> In places where I knew the code reasonably well could tell without much
>> surrounding context. In other places I had to look at the code and
>> deduce proper behavior in the "may" cases -- and often I resorted to
>> spot checking and relying on your reputation & testing to DTRT.
>>
>>
>>>
>>> - known_eq / maybe_eq / known_lt / maybe_lt etc.
>>>
>>> Some functions already use "known" and "maybe", so this would arguably
>>> be more consistent than using "must" and "may".
>>>
>>> - always_eq / sometimes_eq / always_lt / sometimes_lt
>>>
>>> Similar to the previous one in intent. It's just a question of which
>>> wordng is clearer.
>>>
>>> - forall_eq / exists_eq / forall_lt / exists_lt etc.
>>>
>>> Matches the usual logic quantifiers. This seems quite appealing,
>>> as long as it's obvious that in:
>>>
>>> forall_eq (v0, v1)
>>>
>>> v0 and v1 themselves are already bound: if vi == ai + bi*X then
>>> what we really saying is:
>>>
>>> forall X, a0 + b0*X == a1 + b1*X
>>>
>>> Which of those sounds best? Any other suggestions?
>> I can live with any of them. I tend to prefer one of the first two, but
>> it's not a major concern for me. So if you or others have a clear
>> preference, go with it.
>
> Whatever you do use a consistent naming which I guess means
> using known_eq / maybe_eq?
>
> Otherwise ok.
So I think that's the final ack on this series. Richard S. can you
confirm? I fully expect the trunk has moved some and the patches will
need adjustments -- consider adjustments which work in a manner similar
to the patches to date pre-approved.
jeff
