Remove dead store to _Count in _Sort_unchecked and other cleanups#449
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BillyONeal merged 2 commits intomicrosoft:masterfrom Jan 25, 2020
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…were forced to initialize in the constexpr algorithms review by eliminating the variable entirely. * Consistently test _ISORT_MAX with <=, and make that an _INLINE_VAR constexpr variable. * Remove _Count guards of 1 in front of _Insertion_sort_unchecked for consistency. I did performance testing and there was no measurable difference in keeping this check, and it's more code to reason about. * Avoid needless casts of _ISORT_MAX given that it is now a constexpr constant.
BillyONeal
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Jan 24, 2020
CaseyCarter
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Jan 24, 2020
CaseyCarter
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Jan 24, 2020
StephanTLavavej
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Jan 25, 2020
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| if (_Ideal <= 0) { // heap sort if too many divisions |
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I observe that _Ideal should never be negative. It's initially _ULast - _UFirst (non-negative) and then decreases via _Ideal = (_Ideal >> 1) + (_Ideal >> 2). Perhaps an _STL_INTERNAL_CHECK for negative, and an exact == 0 test otherwise? However, there's probably no codegen difference in practice, so I don't really care.
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Codegen is identical except for je vs. jle
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In GH-425 I was forced to add a dead initialization for the _Count variable in _Sort_unchecked in order to comply with constexpr rules. Also, _Sort_unchecked had somewhat complex assignment-in-conditional-expressions going on. This change moves the code around such that the _Count variable is assigned once.
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