[Microbenchmarks] Add benchmark for conditional scalar assignment autovec #295
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…ovec Benchmarks with vs. without autovec for a loop containing conditional scalar assignment (plus a little extra arithmetic as a 'work payload').
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Microbenchmark for FindLast/CSA autovec, as requested on llvm/llvm-project#158088 With just the conditional assignment in the loop, there was no noticeable performance difference. However, when I added a small arithmetic payload I saw a noticeable difference, especially for uint8t. |
MacDue
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MacDue
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Generally seems reasonable to me (bar a few nits), but I've not added a benchmark before, so wait and see if there's any more comments.
MicroBenchmarks/LoopVectorization/ConditionalScalarAssignment.cpp
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| @@ -0,0 +1,118 @@ | |||
| #include <iostream> | |||
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Was going to comment about the license header, but it seems that's not done here (looking at other files).
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Yeah, I wondered about that too.
MicroBenchmarks/LoopVectorization/ConditionalScalarAssignment.cpp
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| // for 'A' in init_data below. | ||
| T Result = 101; | ||
| for (unsigned i = 0; i < ITERATIONS; i++) { | ||
| // Do some work to make the difference noticeable |
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could you add a few more variations, like the minimal case with just a CAS and multiple independent CAS?
| } | ||
| } | ||
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| // Add add auto-vectorized and disabled vectorization benchmarks for math |
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The comment needs updating, currently passes only ty and Threshold, but it might be helpful to also pass a function if it helps to reduce the duplication for additional patterns
| #endif | ||
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| for (auto _ : state) { | ||
| VecFn(&A[0], &B[0], &C[0], Threshold); |
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I am not sure this is working as expected. I think we need something like below to make sure the CAS result is used:
- NoVecFn(&A[0], &B[0], &C[0], Threshold);
+ auto Res = NoVecFn(&A[0], &B[0], &C[0], Threshold);
+ benchmark::DoNotOptimize(Res);
Without a use of the result, compiler is probably able completely remove the variantst that don't have stores in the loop and also remove the unused CAS chain after inlining?
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Benchmarks with vs. without autovec for a loop containing conditional
scalar assignment (plus a little extra arithmetic as a 'work payload').