RFR: 8282365: Consolidate and improve division by constant idealizations [v35]

[Quan Anh Mai]

On Thu, 7 Dec 2023 21:38:11 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   missing include
>
> src/hotspot/share/opto/divnode.hpp line 40:
> 
>> 38: template <class T>
>> 39: void magic_divide_constants(T d, T N_neg, T N_pos, juint min_s, T& c, bool& c_ovf, juint& s);
>> 40: void magic_divide_constants_round_down(juint d, juint& c, juint& s);
> 
> The definitions of these are in new file divconstants.cpp.  So I think these should be in divconstants.hpp.

I see there are multiple cases where a header is defined in multiple source files, and these are used exclusively for `DivNode`s so putting them here seems logical.

> test/hotspot/gtest/opto/test_constant_division.cpp line 29:
> 
>> 27: #include <random>
>> 28: #include <type_traits>
>> 29: #include <vector>
> 
> We mostly don't use C++ standard library facilities in HotSpot, even in tests; see the style guide.
> <type_traits> is permitted.  We have GrowableArray instead of <vector>.  And we have os::random,
> unless this really needs something better (seems unlikely, other than needing to deal with wider
> types than int.)  Also, stdlib includes at the end again (except I think unittest.hpp is supposed to
> _really_ be last.)

I see, for `vector` I did not look it up carefully and thought that we need a VM for `GrowableArray`s, and `<random>` is used mainly for wider types and custom bounds. I have changed them to use what are offered by OpenJDK instead.

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PR Review Comment: https://git.openjdk.org/jdk/pull/9947#discussion_r1424240505
PR Review Comment: https://git.openjdk.org/jdk/pull/9947#discussion_r1424238521