Reduce allocations while enumerating Speller suggestions and improve performance

[h3xds1nz]

Description

Decreases allocations while enumerating suggestions in Speller. Further improves performance, anywhere from 1.5 to 2.5.

• Replace ArrayList with List<string>.
• Replace custom iteration with the base implementation.
• Raises base allocation of items from 1 to 4 as in most cases the number of suggestions more than 1.
• The return type could be an IList<string> or IEnumerable<string> but since it is internal I didn't bother.

1 suggestion (worst case, uncommon)

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	21.56 ns	0.345 ns	0.288 ns	0.0072	1,415 B	120 B
PR__EDIT	14.20 ns	0.292 ns	0.300 ns	0.0076	1,531 B	128 B

2 suggestions

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	38.18 ns	0.292 ns	0.273 ns	0.0095	1,910 B	160 B
PR__EDIT	18.31 ns	0.269 ns	0.251 ns	0.0076	1,594 B	128 B

3 suggestions

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	52.59 ns	0.659 ns	0.584 ns	0.0129	2,078 B	216 B
PR__EDIT	21.20 ns	0.213 ns	0.178 ns	0.0076	1,661 B	128 B

6 suggestions

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	82.26 ns	1.224 ns	1.085 ns	0.0181	2,874 B	304 B
PR__EDIT	55.22 ns	0.851 ns	0.754 ns	0.0129	1,076 B	216 B

8 suggestions

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	99.92 ns	0.714 ns	0.557 ns	0.0181	3,032 B	304 B
PR__EDIT	58.23 ns	0.838 ns	0.743 ns	0.0129	1,160 B	216 B

9 suggestions

Method	Mean [ns]	Error [ns]	StdDev [ns]	Gen0	Code Size [B]	Allocated [B]
Original	125.89 ns	1.450 ns	1.356 ns	0.0272	3,056 B	456 B
PR__EDIT	78.59 ns	1.368 ns	1.279 ns	0.0219	1,209 B	368 B

Benchmark code

[Benchmark]
public void Original()
{
    foreach (string suggestion in Suggestions)
        EmptyMethod(suggestion);
}

[Benchmark]
public void PR__EDIT()
{
    foreach (string suggestion in SuggestionsV2)
        EmptyMethod(suggestion);
}

[MethodImpl(MethodImplOptions.NoInlining)]
private int EmptyMethod(string suggestions) => suggestions[0];

public IEnumerable<string> Suggestions
{
    get
    {
        IList suggestions = _speller.GetSuggestionsForError();

        for (int i = 0; i < suggestions.Count; i++)
        {
            yield return (string)suggestions[i];
        }
    }
}

public IEnumerable<string> SuggestionsV2
{
    get => _speller.GetSuggestionsForErrorV2();
}

private readonly Speller _speller = new();

public class Speller
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public IList GetSuggestionsForError()
    {
        ArrayList suggestions = new ArrayList(1);

        suggestions.Add("hannah");
        suggestions.Add("lannal");
        suggestions.Add("hannah");

        suggestions.Add("hannah");
        suggestions.Add("lannal");
        suggestions.Add("hannah");

        suggestions.Add("lannal");
        suggestions.Add("hannah");

        suggestions.Add("hannah");

        return suggestions;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public List<string> GetSuggestionsForErrorV2()
    {
        List<string> suggestions = new(4);

        suggestions.Add("hannah");
        suggestions.Add("lannal");
        suggestions.Add("hannah");

        suggestions.Add("hannah");
        suggestions.Add("lannal");
        suggestions.Add("hannah");

        suggestions.Add("lannal");
        suggestions.Add("hannah");

        suggestions.Add("hannah");

        return suggestions;
    }
}

Customer Impact

Improved performance, decrease allocations.

Regression

No.

Testing

Local build, verifying Speller/Suggestions functionality.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow

[rchauhan18]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[harshit7962]

@h3xds1nz Thank you for your contributions.

[h3xds1nz]

@harshit7962 Thank you.