Use MoveToImmutable for ImmutableArray<T>.Builder in ILCompiler.Compiler - #134426
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Update ImmutableArray<T>.Builder usages in ILCompiler.Compiler to call MoveToImmutable instead of ToImmutable/ToImmutableArray, specifying an initial capacity where it was missing. This avoids reallocating the backing array as it grows, as well as the extra copy when creating the ImmutableArray<T>. Also replace the LINQ Skip(1) in ReflectionMethodBodyScanner with a span slice over the underlying list. The overall performance impact is small, but this removes unnecessary allocations and copies. Changes: - AttributeDataFlow,MethodProxy,TypeProxy - Use MoveToImmutable instead of ToImmutableArray - TrimAnalysisMethodCallPattern - Specify capacity and use MoveToImmutable instead of ToImmutableArray - ReflectionMethodBodyScanner - Use CollectionsMarshal.AsSpan and Slice instead of the LINQ Skip
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Copilot review overview
🟡 Changes recommended
Add the requested representative benchmark or allocation profile.
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Review effort: Lite
Findings: 1
What changed in this PR
This PR reduces ILCompiler dataflow allocations by using ImmutableArray builder moves and span slicing.
Changes:
- Uses
MoveToImmutableand builder capacities. - Replaces LINQ
Skip(1)withCollectionsMarshal.AsSpan(...).Slice(1). - Review note: add a representative benchmark or allocation profile for the optimization.
| File | Description |
|---|---|
src/coreclr/tools/Common/Compiler/Dataflow/TypeProxy.cs |
Moves generic parameter builder contents directly. |
src/coreclr/tools/Common/Compiler/Dataflow/MethodProxy.cs |
Moves method generic parameter builder contents directly. |
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/TrimAnalysisMethodCallPattern.cs |
Adds capacity and avoids immutable-array copies. |
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/ReflectionMethodBodyScanner.cs |
Uses span slicing instead of Skip(1). |
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Dataflow/AttributeDataFlow.cs |
Moves fixed attribute arguments directly. |
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This was referenced Sep 24, 2026
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Sep 25, 2026
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Summary
This PR updates
ImmutableArray<T>.Builderusages inILCompiler.Compilerto callMoveToImmutableinstead ofToImmutable/ToImmutableArray, specifying an initial capacity where it was missing. This avoids reallocating the backing array as it grows, as well as the extra copy when creating theImmutableArray<T>.Also replace the LINQ
Skip(1)inReflectionMethodBodyScannerwith a span slice over the underlying list.The overall performance impact is small, but this removes unnecessary allocations and copies.
Changes
MoveToImmutableinstead ofToImmutableArrayMoveToImmutableinstead ofToImmutableArrayCollectionsMarshal.AsSpanandSliceinstead of the LINQSkipValidation
I ran the NativeAOT smoketests and
ILCompiler.*.Testsusing the following commands and confirmed that they all passed in local.