Add strength reduction benchmarks #4317
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This adds strength reduction benchmarks for arrays of a few different element sizes, motivated by the differences in codegen. 2: load 3: lea + load 4: load 8: load 12: lea + load 16: shl + load 29: imul Each size has 3 variants of benchmarks: an array version, a span version, and a fully strength reduced manual version. The JIT is expected to be able to transform the array version into the strength reduced version soon. The span version will also be transformed, but not quite all the way (the strength reduction will not be able to fold in the base byref of the span).
21 tasks
3 tasks
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I don't think the CI failures are related. |
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Yes, the current ci failures do not seem to be related, is this ready for review and merge? |
Yeah, this is ready. |
LoopedBard3
approved these changes
Jul 18, 2024
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This adds strength reduction benchmarks for arrays of a few different element sizes, motivated by the differences in codegen. The element sizes give different characteristics of how we access each element. For x64, the current instruction codegen looks like:
2: load
3: lea + load
4: load
8: load
12: lea + load
16: shl + load
29: imul + load
Each size has 3 variants of benchmarks: an array version, a span version, and a fully strength reduced manual version. The JIT is expected to be able to transform the array version into the strength reduced version soon. The span version will also be transformed, but not quite all the way (the strength reduction will not be able to fold in the base byref of the span).
There is one current annoyance to work around in the JIT: we do not align the strength-reduced versions of the loops because they end up being "too small", meaning that they still fit within a single cache line. However, it turns out alignment is still beneficial in these cases, and this skews the results compared to the non-strength reduced versions. I have opened dotnet/runtime#104665 about this. To work around the problem in these benchmarks I have added a superfluous bitwise or operation in the body of all the loops.
On my Intel CPU the current results are: