`Vector<T>` inlining heuristics cause cold throw helpers to be inlined

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#119,251 2 comments 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp
Domain
performance

Research direction

Start with the minimal C# repro in the issue and inspect its generated output on the linked Compiler Explorer page, then read the referenced PR discussion about Vector inlining heuristics. Done means the cold throw helper is no longer inlined into the hot path merely because the code involves Vector.

Written by the indexing model from the issue text.

Description

area-CodeGen-coreclr

As per https://github.com/dotnet/runtime/pull/119234#issuecomment-3242883614, Vector<T> currently has special inlining profitability heuristics that encourage inlining. This can result in undesirable cases where cold throw helpers are inlined into hot code paths simply because they involve Vector<T>.

Minimal repro:

using System;
using System.Numerics;
public class C {
    public void M(Vector<float> value) {
        ArgumentOutOfRangeException.ThrowIfEqual(value, Vector<float>.Zero);
    }
}

https://csharp.godbolt.org/z/rqxa1q7G6

Dominant language
C#
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