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[Analyzer Proposal]: Remove redundant cast on vectors #103557
Description
Background and motivation
Strong typing for SIMD often leads to frequent casts from one type of Vector to another (typically, no-op in codegen). Sometimes user might accidentally introduce redundant casts that can be safely removed. I propose an analyzer that highlights such casts. Example:
return AdvSimd.MultiplyWideningLowerAndAdd(
AdvSimd.ShiftLeftLogical(
AdvSimd.AddPairwiseWidening(
AdvSimd.Multiply(b.AsInt32(),
AdvSimd.ReverseElement32(a).AsInt32()).AsUInt32()).AsInt64(), 32),
AdvSimd.ExtractNarrowingLower(a),
AdvSimd.ExtractNarrowingLower(b)).As<long, T>();Here I had to insert quite a few casts to make it work as expected and it's not obvious whether some of them might be redundant or not. It's not a codegen issue, just an opportunity to make code smaller = easier to read.
API Usage
Vector128<ulong> v = Vector128.Create(ulong.MaxValue);
DoWork(v.AsUInt64()); // Flagged with "redundant cast"Alternative Designs
No response
Risks
N/A
Activity
EgorBo commentedon Jun 17, 2024
cc @tannergooding
dotnet-policy-service commentedon Jun 17, 2024
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tannergooding commentedon Jun 17, 2024
Notably this is always a no-op, it's fully elided in importation and never produces IR today (barring the case we throw because it is invalid, but that's also statically determined).
We can likely just close this and lump it together with the already approved: #82488, which tracks a general analyzer for suggesting more optimal SIMD patterns.