[pytorch][te] Add compilation time benchmark (#46124)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46124
We want to make sure we can actually fuse kernels within a fairly
tight time budget. So here's a quick benchmark of codegen for a simple
pointwise activation function (swish). I kept all the intermediate tensors
separate to force TE to actually do inlining.
Test Plan:
```
buck run mode/opt //caffe2/benchmarks/cpp/tensorexpr:tensorexpr_bench
```
I've only run in debug mode so results aren't super meaningful, but even in
that mode it's 18ms for compilation, 15 of which are in llvm.
Update, opt build mode:
```
----------------------------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------------------------
BM_CompileSwish 5123276 ns 5119846 ns 148
BM_CompileSwishLLVMOnly 4754361 ns 4753701 ns 160
```
Reviewed By: asuhan
Differential Revision: D24232801
fbshipit-source-id: d58a8b7f79bcd9244c49366af7a693e09f24bf76
