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Use memset in even more cases - #1273

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Stephan T. Lavavej (StephanTLavavej) merged 17 commits into
microsoft:masterfrom
AdamBucior:fill_zero_optimization
Oct 29, 2020
Merged

Use memset in even more cases#1273
Stephan T. Lavavej (StephanTLavavej) merged 17 commits into
microsoft:masterfrom
AdamBucior:fill_zero_optimization

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@AdamBucior

@AdamBucior Adam Bucior (AdamBucior) commented Sep 5, 2020 •
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Another small PR to optimize (ranges::)(uninitialized_)fill(_n). I applied the optimization only to the _HAS_IF_CONSTEXPR branch because without if constexpr it becomes very tricky to implement and I don't know how long the !_HAS_IF_CONSTEXPR branch will live. Part of #431.

@AdamBucior
Adam Bucior (AdamBucior) requested a review from a team as a code owner September 5, 2020 10:56
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Sep 23, 2020

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I pushed a merge to uninitialized_fill_n() in - it needed a bit of manual surgery, and I think I got it right, but please double-check.

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Adam Bucior (AdamBucior) commented Sep 23, 2020

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I pushed a merge to uninitialized_fill_n() in - it needed a bit of manual surgery, and I think I got it right, but please double-check.

Looks good

CaseyCarter
Casey Carter (CaseyCarter) reviewed Sep 24, 2020
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static_assert is_scalar
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Co-authored-by: Casey Carter
AdamBucior
Adam Bucior (AdamBucior) commented Sep 24, 2020
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Adam Bucior (AdamBucior) commented Sep 24, 2020
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Casey Carter (CaseyCarter) approved these changes Oct 3, 2020
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@CaseyCarter Casey Carter (CaseyCarter) left a comment •
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LGTM! Thanks for the extra test coverage.

@CaseyCarter Casey Carter (CaseyCarter) removed their assignment Oct 3, 2020
StephanTLavavej
Stephan T. Lavavej (StephanTLavavej) requested changes Oct 28, 2020
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Thanks for implementing this optimization! I found one bug involving floating-point negative zero, but otherwise this looks very solid.

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@StephanTLavavej
Avoid Clang's -Wzero-as-null-pointer-constant warning.
3a937b3 
`static_cast<_Ty>(0)` emits this warning for object pointers, function
pointers, and `nullptr_t`. We can avoid this warning by using empty
braces to request zero-initialization.
@StephanTLavavej
Portably test for negative zero.
2866b64
@StephanTLavavej
Test allocate_shared.
3d21ed4
@StephanTLavavej
Merge branch 'master' into gh1273_memset
d3fd586
@StephanTLavavej

Stephan T. Lavavej (StephanTLavavej) commented Oct 29, 2020

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Looks great! I've pushed three small changes (FYI Casey Carter (@CaseyCarter)) and merged with master (without conflicts), so I can add your PR to today's batch for merging.

  • Avoid Clang's -Wzero-as-null-pointer-constant warning.
    • static_cast<_Ty>(0) emits this warning for object pointers, function pointers, and nullptr_t. We can avoid this warning by using empty braces to request zero-initialization.
  • Portably test for negative zero.
    • We conventionally avoid using internal machinery in tests unless it allows something to be tested that would be difficult otherwise. Instead of _Bit_cast, we can use 's signbit() to detect negative zero.
  • Test allocate_shared.

@StephanTLavavej
Stephan T. Lavavej (StephanTLavavej) merged commit a27d894 into microsoft:master Oct 29, 2020
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Stephan T. Lavavej (StephanTLavavej) commented Oct 29, 2020

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Thanks again for this optimization, automatically making user code faster! This will ship in VS 2019 16.9 Preview 2. 🎉

@AdamBucior
Adam Bucior (AdamBucior) deleted the fill_zero_optimization branch October 29, 2020 08:53
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@StephanTLavavej Stephan T. Lavavej (StephanTLavavej) StephanTLavavej approved these changes
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@CaseyCarter Casey Carter (CaseyCarter) CaseyCarter approved these changes
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