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⚡ Bolt: [Optimize VirtualMemory bounds checking in hot path] - #84

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manupawickramasinghe wants to merge 3 commits into
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perf-optimize-vmem-8939662575122251057
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⚡ Bolt: [Optimize VirtualMemory bounds checking in hot path]#84
manupawickramasinghe wants to merge 3 commits into
mainfrom
perf-optimize-vmem-8939662575122251057

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@manupawickramasinghe

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💡 What

Replaced standard List<T> indexer accesses with System.Runtime.InteropServices.CollectionsMarshal.AsSpan(_regions) combined with ref var references in core VirtualMemory memory translation operations.

🎯 Subsystem & Bottleneck

  • Subsystem: Guest MMU
  • Target File(s): src/SharpEmu.Core/Memory/VirtualMemory.cs
  • Bottleneck Addressed: CPU instruction overhead caused by redundant List<T> bounds checking and struct copying inside the tight memory read/write and validation loops.

📜 Git & Contributor Context

  • Recent File History: Checked git log and blame; file is stable, last modified roughly 14 days ago.
  • Conflict Check: Verified change does not overlap with recent commits or reverted attempts.

📊 Measured Performance Impact

  • Allocation Delta: N/A (Already 0B, focus was on CPU overhead).
  • Computational Impact: Replaced implicit bounds-checked array access with unchecked O(1) span direct access (span[index]), reducing branching in hot paths.

🔬 Verification Checklist

  • Executed dotnet test (All tests passed)
  • Verified zero unexpected allocations in hot path
  • Verified formatting with dotnet format
  • Confirmed thread safety and emulation accuracy (AsSpan operates safely inside lock(_gate))

PR created automatically by Jules for task 8939662575122251057 started by @manupawickramasinghe

Replaces standard `List<T>` indexing with `CollectionsMarshal.AsSpan`
and uses `ref var` references within hot-path VirtualMemory methods.
This avoids bounds-checking overhead per iteration and prevents
value-copying of the `MappedRegion` elements on every read/write cycle.

Co-authored-by: manupawickramasinghe <73810867+manupawickramasinghe@users.noreply.github.com>
Copilot AI lite review requested due to automatic review settings September 8, 2026 19:32
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Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

google-labs-jules Bot and others added 2 commits September 8, 2026 19:36
Replaces standard `List<T>` indexing with `CollectionsMarshal.AsSpan`
and uses `ref var` references within hot-path VirtualMemory methods.
This avoids bounds-checking overhead per iteration and prevents
value-copying of the `MappedRegion` elements on every read/write cycle.

Co-authored-by: manupawickramasinghe <73810867+manupawickramasinghe@users.noreply.github.com>
Replaces standard `List<T>` indexing with `CollectionsMarshal.AsSpan`
and uses `ref var` references within hot-path VirtualMemory methods.
This avoids bounds-checking overhead per iteration and prevents
value-copying of the `MappedRegion` elements on every read/write cycle.

Co-authored-by: manupawickramasinghe <73810867+manupawickramasinghe@users.noreply.github.com>
@manupawickramasinghe

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Applied CollectionsMarshal.AsSpan and ref var region optimizations into main via commit 9949fed. Closed as merged.

@google-labs-jules

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Applied CollectionsMarshal.AsSpan and ref var region optimizations into main via commit 9949fed. Closed as merged.

Understood. Acknowledging that this work is now merged and stopping work on this task.

manupawickramasinghe added a commit that referenced this pull request Sep 9, 2026
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2 participants