pytorch

df5b4696 - [Pytorch] Specialize guts of c10::optional for 32-bit scalars (#47015)

[Pytorch] Specialize guts of c10::optional for 32-bit scalars (#47015) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47015 c10::optional has non-trivial copy and move operations always. This change specializes it for 32-bit scalars so that it has trivial copy and move operations in that case. Ideally, we would instead rely on P0602 "variant and optional should propagate copy/move triviality" and use `std::optional` (or implement that functionality ourselves). We can't use `std::optional` because we are stuck with C++14. Implementing the full P0602 ourselves would add even more complexity. We could do it, but this should be a helpful first step. ghstack-source-id: 115886743 Test Plan: Collect Callgrind instruction counts for `torch.empty(())`. Data: Make empty c10-ful (https://github.com/pytorch/pytorch/pull/46092): ``` <torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.CallgrindStats object at 0x7ffaed1128e0> torch.empty(()) All Noisy symbols removed Instructions: 648005 632899 Baseline: 4144 3736 100 runs per measurement, 1 thread ``` This diff atop #46092: ``` <torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.CallgrindStats object at 0x7f943f1dc8e0> torch.empty(()) All Noisy symbols removed Instructions: 602347 591005 Baseline: 4106 3736 100 runs per measurement, 1 thread ``` (6.6% improvement vs #46092) Pass optionals by const reference (https://github.com/pytorch/pytorch/pull/46598) ``` <torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.CallgrindStats object at 0x7f1abb3988e0> torch.empty(()) All Noisy symbols removed Instructions: 601349 590005 Baseline: 4162 3736 100 runs per measurement, 1 thread ``` (6.8% improvement vs #46092) This diff atop #46598 (i.e., both together) ``` <torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.CallgrindStats object at 0x7f9577c22850> torch.empty(()) All Noisy symbols removed Instructions: 596095 582451 Baseline: 4162 3736 100 runs per measurement, 1 thread Warning: PyTorch was not built with debug symbols. Source information may be limited. Rebuild with REL_WITH_DEB_INFO=1 for more detailed results. ``` (another 1.3% savings!) #46598 outperformed this change slightly, and combining the two leads to further benefits. I guess we should do both! (Though I still don't understand why passing optionals that should fit in a register by const reference would help...) Reviewed By: smessmer Differential Revision: D24552280 fbshipit-source-id: 4d93bfcffafebd8c01559398513fa6b9db959d11