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Allow GlobalizationMode.Invariant = false to be substituted by the trimmer. #47999

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Feb 9, 2021
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Allow GlobalizationMode.Invariant = false to be substituted by the trimmer. #47999

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1 change: 1 addition & 0 deletions src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Substitutions.Shared.xml
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Expand Up @@ -8,6 +8,7 @@
</type>
<type fullname="System.Globalization.GlobalizationMode">
<method signature="System.Boolean get_Invariant()" body="stub" value="true" feature="System.Globalization.Invariant" featurevalue="true" />
<method signature="System.Boolean get_Invariant()" body="stub" value="false" feature="System.Globalization.Invariant" featurevalue="false" />
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Are there other cases like this? I'm wondering whether we need more cases of handling both the true and false values, and if so, if there's a more general feature needed here, where the linker sees a line like:

<method signature="System.Boolean get_Invariant()" body="stub" feature="System.Globalization.Invariant" featurevalue="true" />

and automatically propagates featurevalue to value, or something like that.

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I had proposed this in chat to @eerhardt the other day since it means we are potentially leaving behind bits of "unused" code that are statically known to only be true/false and therefore have no side effects.

dotnet/linker#1106 (comment) is a related example where just leaving the get_IsSupported() methoods can lead to larger downstream impact due to inheritance chains.

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In all our existing feature switches, only 1 value will trim any substantial piece of code. For Invariant, I wasn't aware how much unnecessary code was still being rooted for the default setting. I thought only Invariant=true would trim a decent amount of code.

But I can imagine this being beneficial in other feature switches in the future.

cc @marek-safar @vitek-karas @sbomer - thoughts?

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A related bit is that even needing to hardcode get_Invariant and others seems potentially unnecessary in certain cases

One would expect the linker could recognize the general pattern of static readonly bool s_name = AppContext.TryGetSwitch("", out bool result) ? result : default (or others) and that we wouldn't need to hardcode a table of substitutions outside of more complicated scenarios.
It, plus knowing that static readonly <primitive> name = value can't change after being set seem like generally good things to recognize as they can lead to later downstream optimizations and therefore trimming opportunities

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If it's common we could make syntax which would be able to substitute the value directly from the feature value. Note that even boolean features have 3 values: true, false, not-set. I assume the "not-set" would mean no substitution (unless the defaultfeaturevalue is used).

If this is the only place right now, it's probably not worth it though.

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One would expect the linker could recognize the general pattern

That could work for other cases, but it doesn't work for this case:

runtime/src/libraries/System.Private.CoreLib/src/System/Globalization/GlobalizationMode.Unix.cs

Lines 10 to 38 in 8a52f1e

internal static bool Invariant { get; } = GetGlobalizationInvariantMode();
internal static bool UseNls => false;
private static bool GetGlobalizationInvariantMode()
{
bool invariantEnabled = GetInvariantSwitchValue();
if (!invariantEnabled)
{
if (TryGetAppLocalIcuSwitchValue(out string? icuSuffixAndVersion))
{
LoadAppLocalIcu(icuSuffixAndVersion);
}
else
{
int loaded = Interop.Globalization.LoadICU();
if (loaded == 0 && !OperatingSystem.IsBrowser())
{
string message = "Couldn't find a valid ICU package installed on the system. " +
"Set the configuration flag System.Globalization.Invariant to true if you want to run with no globalization support.";
Environment.FailFast(message);
}
// fallback to Invariant mode if LoadICU failed (Browser).
return loaded == 0;
}
}
return invariantEnabled;
}

</type>
<type fullname="System.LocalAppContextSwitches">
<method signature="System.Boolean get_EnableUnsafeUTF7Encoding()" body="stub" value="false" feature="System.Text.Encoding.EnableUnsafeUTF7Encoding" featurevalue="false" />
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