Don't trigger ICU loading in string.ToUpperInvariant

[EgorBo]

Contributes to #120407

It looks like even a simple

System.Console("Hello world");

may trigger ICU load unnecessarily via string.ToUpperInvariant calls:

Another source of these string.ToUpperInvariants are EventSource (over EventSources' names to generate guids) - we plan to remove those, though.

For most app the ICU most likely will be loaded anyway, but IMO if it doesn't take too much of efforts, we should delay/avoid it. In this PR it is achieved by introducing a few extra null check.

Perf-traces for a hello world:

• Main
• PR

Also, perf improvements for the InvariantGlobalization mode: EgorBot/runtime-utils#521

[Copilot]

Pull Request Overview

This PR optimizes string case conversion to avoid unnecessary ICU loading during simple operations like string.ToUpperInvariant() and string.ToLowerInvariant(). The change addresses performance concerns where even basic console output could trigger ICU initialization unnecessarily.

Key changes:

• Introduced new static methods ToUpperInvariant and ToLowerInvariant in TextInfo that bypass TextInfo.Invariant property access
• Modified the ChangeCaseCommon methods to accept nullable TextInfo instances, using null to represent invariant culture
• Updated all call sites to use the new pattern where null TextInfo indicates invariant culture processing

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Private.CoreLib/src/System/String.Manipulation.cs	Updated ToUpperInvariant and ToLowerInvariant to call new static TextInfo methods
src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.cs	Added static ToUpperInvariant/ToLowerInvariant methods and refactored ChangeCaseCommon to accept nullable TextInfo

[jkotas]

cc @tarekgh

[EgorBo]

Ah, it's actually a bit more complicated because bool GlobalizationMode.InvariantNoLoad despite the name actually triggers the ICU (on non BROWSER targets).

It returns Settings.Invariant where Settings has an explicit static cctor explicitly loading the ICU. it probably can be fixed if it won't break the IL linker behavior.

[jkotas]

I think you would have to frontload the speculative ascii-only path before any GlobalizationMode.Invariant checks.

[EgorBo]

@EgorBot -amd -arm --envvars DOTNET_SYSTEM_GLOBALIZATION_INVARIANT:1

using BenchmarkDotNet.Attributes;

public class Benchmarks
{
    [Benchmark]
    [Arguments(".NET Runtime uses third-party libraries or other " +
               "resources that may be distributed under licenses " +
               "different than the .NET Runtime software.")]

    [Arguments("runtime uses third-party libraries or other " +
               "resources that may be distributed under licenses")]

    [Arguments("runtime")]
    public string ToLower(string data) => data.ToLowerInvariant();
}

[EgorBo]

I think you would have to frontload the speculative ascii-only path before any GlobalizationMode.Invariant checks.

Right, I thought I could just avoid loading ICU at all triggered by if (GlobalizationMode.Invariant) but looks a lot of places rely on this condition to actually load it and crash badly by invoking ICU APIs on a non-loaded ICU.

I've slightly changed the code so the ASCII path is always executed first (for Invariant mode or when IsAsciiCasingSameAsInvariant is true) and if the input is full ASCII ICU won't be loaded for these paths.

Previously we were unconditionally using the special path for invariant mode and that path was quite slow for full ASCII as it was a scalar impl. So presumably my PR improves ASCII inputs for the Invariant mode but regresses non-ASCII ones. I assume the inputs are more likely to be ASCII in the Invariant mode so it sounds like a reasonable trade-off.

[EgorBo]

Flamegraphs for before-after for a hello world:

• Main
• PR

Perf improvements for ASCII only inputs in the InvariantGlobalization mode: EgorBot/runtime-utils#521

[tarekgh]

        public string ToLower(string str)
        {
            ArgumentNullException.ThrowIfNull(str);

            if (GlobalizationMode.Invariant)
            {

Is this check needed anymore?

---

Refers to: src/libraries/System.Private.CoreLib/src/System/Globalization/TextInfo.cs:176 in 5fa74a0. [](commit_id = 5fa74a0, deletion_comment = False)

[tarekgh]

Would this affect how trimming works? I recall that trimming used to depend on GlobalizationMode.Invariant, but that’s no longer as straightforward as before. It would be good to double-check this with the trimming team.

[tarekgh]

LGTM!