The events introduced in #2519 timed only the five per-entity DoDecompile
overloads, allocated a Stopwatch and the member's FullName even when no
trace session was attached, and reported whole milliseconds, which rounds
almost every member to zero. Flat one-shot events also gave PerfView and
dotnet-trace no way to show durations or nesting, and the actually
expensive stages (type system initialization, assembly resolution probing,
the IL/AST transform pipelines, whole-project decompilation) were not
instrumented at all.
Start/Stop event pairs let trace viewers derive duration and nesting from
event timestamps, keywords let a session enable only the areas of
interest, and every call site is gated on IsEnabled() so tracing costs a
branch when disabled. Per-transform events are Verbose because of their
volume; unlike the STEP/Stepper mechanism they work in Release builds.
EventSource is in-box for netstandard2.0 and flows over both ETW and
EventPipe, so this stays cross-platform with no new dependency.
Assisted-by: Claude:claude-fable-5:Claude Code
Hosts without a .NET Framework installation (e.g. Linux and macOS) have
no GAC; the only system-wide assembly store there is the shared-framework
directory of the runtime executing the decompiler, and
UniversalAssemblyResolver only consulted it through the version <= 4.0
legacy fallback. This made e.g. the type-forwards of a netstandard facade
(pointing to a versioned System.Runtime) unresolvable, which left
well-known types like Nullable<T> without a definition and among other
things misaligned nullability decoding (Nullable<T> occupies no slot in
the nullable metadata, so it must be recognized).
On Windows nothing the GAC answered changes; the new fallback only adds
resolutions that previously failed outright.
Assisted-by: Claude:claude-fable-5:Claude Code
DecompilerTypeSystem uses this to resolve/load multiple assemblies in parallel.
Unfortunately this doesn't gain us any performance yet in ILSpy because there we have a global assembly-loader-lock :(