IL emit hack: direct token writes via UnsafeAccessorType (NET10+), caller-hint overloads, and benchmark harness by Copilot · Pull Request #515 · dadhi/FastExpressionCompiler

Copilot · 2026-04-13T22:04:03Z

Wires the NET10+ SUPPORTS_IL_EMIT_HACK path into FEC's emission loop so all token-emitting Demit calls (MethodInfo, ConstructorInfo, FieldInfo) bypass ILGenerator.Emit() overhead in a single place, with no call-site changes.

What the hack does

Instead of ILGenerator.Emit(OpCodes.Call, meth) — which switches on operand type, calls EnsureCapacity, looks up DynamicScope.GetTokenFor() (hashtable) — the hack writes bytes directly:

// Hack path (non-generic types, DynamicILGenerator only)
mILStream[mLength++] = (byte)OpCodes.Call.Value;
ref var tokens = ref GetScopeTokens(il);   // one FieldInfo.GetValue for m_scope
tokens.Add(meth.MethodHandle);             // direct List.Add
BinaryPrimitives.WriteInt32LittleEndian(mILStream.AsSpan(mLength), (tokens.Count - 1) | 0x06000000);
mLength += 4;
UpdateStackSize(il, opcode, stackChange);

Changes

`ILGeneratorTools` (`FastExpressionCompiler.cs`)

#define SUPPORTS_IL_EMIT_HACK under #if NET10_0_OR_GREATER
UseILEmitHack flag — starts false; enabled at end of DynamicMethodHacks static init once _mScopeField is confirmed resolved
Demit(il, opcode, MethodInfo/ConstructorInfo/FieldInfo) gain #if SUPPORTS_IL_EMIT_HACK fast paths — all ~92 token-emitting call sites in FEC benefit automatically
Caller-hint specialized helpers: DemitCallStaticVoid, DemitCallStatic, DemitCallInstanceVoid, DemitCallInstance, DemitNewobj — skip IsStatic/ReturnType/GetParameters when the call site already knows them
Specialized field helpers: DemitLdfld, DemitStfld, DemitLdsfld, DemitLdflda — hardcode the opcode and stack change, bypassing the runtime opcode switch in HackEmitField; all 38 field-access call sites updated to use these
CanUseHackEmit(declaringType, il) — single inlinable guard deduplicating the DynamicILGeneratorType + non-generic check across all helpers
HackEmitMethod, HackEmitCtor, HackEmitField guards compressed to single expressions

`DynamicMethodHacks`

_mScopeField static + GetScopeTokens(il) — resolves DynamicScope.m_tokens ref (one FieldInfo.GetValue for m_scope, then UAT for m_tokens)
HackEmitMethodToken, HackEmitFieldToken (promoted to internal), HackEmitMethod, HackEmitCtor, HackEmitField core helpers

Fallbacks (correctness)

Case	Reason
Generic / array declaring type	Requires internal `GenericMethodInfo`/`GenericFieldInfo` — cannot construct without reflection
`RuntimeILGenerator` (e.g. `MethodBuilder.GetILGenerator()`)	`m_scope` only exists on `DynamicILGenerator`

Benchmark & tests

net10.0 added to FastExpressionCompiler.Benchmarks.csproj
EmitHacks.Net10Emit benchmark comparing baseline il.Emit, Demit_NoHack, Demit_WithHack, raw UAT hack
EmitHacksTest: DynamicMethod_Demit_WithHack / DynamicMethod_Demit_NoHack round-trip tests

…t helpers, NET10 benchmark class Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/dc0b3120-928b-481e-ac2d-183f3609f945 Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

… duplication Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/dc0b3120-928b-481e-ac2d-183f3609f945 Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

dadhi

Analyze callsites and repeated condition checks through collchain, the goal is to benifit from our use pattern and simplify / avoid garbage code along the call chain if we akready checked the invariants in the boundaries.
Also compact comments a bit, more focus and meaning and less buatifying fences and non default unicode symbols please

dadhi · 2026-04-14T05:56:29Z

src/FastExpressionCompiler/FastExpressionCompiler.cs

+            // Fall back for methods on generic/array types: DynamicScope requires GenericMethodInfo
+            // (an internal runtime type) for these; we cannot construct it without reflection overhead.
+            var declaringType = meth.DeclaringType;
+            if (declaringType != null && (declaringType.IsGenericType || declaringType.IsArray))


I already saw this combination for specialized emit, let compress it to the same inliniable check method

Done in 0324a82. The two-condition guard is now a single expression: if (il.GetType() != DynamicILGeneratorType || (dt != null && (dt.IsGenericType || dt.IsArray))) { il.Emit(opcode, meth); return; }

dadhi · 2026-04-14T05:57:10Z

src/FastExpressionCompiler/FastExpressionCompiler.cs

+
+            // Fall back for ctors on generic/array types
+            var declaringType = ctor.DeclaringType;
+            if (declaringType != null && (declaringType.IsGenericType || declaringType.IsArray))


The same compressiin needed

Done in 0324a82 — same single-expression guard applied to HackEmitCtor.

dadhi · 2026-04-14T05:57:57Z

src/FastExpressionCompiler/FastExpressionCompiler.cs

+            // calls FieldInfo.GetFieldFromHandle(handle) without a type context, which throws for generic types.
+            // Also DynamicILGenerator.Emit always stores GenericFieldInfo (not RuntimeFieldHandle) for such fields.
+            var declaringType = field.DeclaringType;
+            if (declaringType != null && (declaringType.IsGenericType || declaringType.IsArray))


Again, can be a one liner check with method

Done in 0324a82 — same single-expression guard applied to HackEmitField.

dadhi · 2026-04-14T05:59:21Z

src/FastExpressionCompiler/FastExpressionCompiler.cs

+            //   Ldsfld/Ldsflda: push value/addr          → net +1
+            //   Stsfld:        pop value                 → net -1
+            int stackChange;
+            if (opcode.Equals(OpCodes.Ldfld) || opcode.Equals(OpCodes.Ldflda))


Can we specialize it more for specific store and load and remove the checks.

Done in 0324a82. Added DemitLdfld, DemitStfld, DemitLdsfld, DemitLdflda helpers that hardcode the opcode and stack change, bypassing the runtime opcode switch in HackEmitField. All 38 call sites updated to use the specialized versions. HackEmitFieldToken promoted to internal so ILGeneratorTools calls it directly.

…, update call sites, compact comments Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/9613f5f4-79a9-4a47-ad46-14c291909fb4 Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

Copilot · 2026-04-14T06:17:32Z

Analyze callsites and repeated condition checks through collchain, the goal is to benifit from our use pattern and simplify / avoid garbage code along the call chain if we akready checked the invarian...

Done in 0324a82:

All unicode box-drawing fences (─────), bullets (•), and arrows (→) removed from comments and replaced with plain text
HackEmitMethod/HackEmitCtor/HackEmitField guards compressed to single expressions
Added DemitLdfld/DemitStfld/DemitLdsfld/DemitLdflda so call sites that know the field opcode skip both the HackEmitField dispatch and the HackEmitFieldToken opcode switch — 38 call sites updated

Initial plan

7c95047

Copilot AI assigned Copilot and dadhi Apr 13, 2026

Copilot AI mentioned this pull request Apr 13, 2026

Use UnsafeAccessor (NET8+) and UnsafeAccessorType (NET10+) for non-public IL generator internals #510

Draft

Copilot started work on behalf of dadhi April 13, 2026 22:04 View session

Copilot AI and others added 2 commits April 13, 2026 22:31

Add IL emit hack: SUPPORTS_IL_EMIT_HACK, UseILEmitHack flag, hack emi…

f86f658

…t helpers, NET10 benchmark class Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/dc0b3120-928b-481e-ac2d-183f3609f945 Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

Fix capacity check (>= -> >), extract CanUseHackEmit helper to reduce…

5763323

… duplication Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/dc0b3120-928b-481e-ac2d-183f3609f945 Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Use UnsafeAccessor for non-public IL generator internals~~ IL emit hack: direct token writes via UnsafeAccessorType (NET10+), caller-hint overloads, and benchmark harness Apr 13, 2026

Copilot finished work on behalf of dadhi April 13, 2026 22:37

Copilot AI requested a review from dadhi April 13, 2026 22:37

dadhi requested changes Apr 14, 2026

View reviewed changes

Copilot started work on behalf of dadhi April 14, 2026 06:02 View session

Compress HackEmit* guards, add DemitLdfld/Stfld/Ldsfld/Ldflda helpers…

0324a82

…, update call sites, compact comments Agent-Logs-Url: https://github.com/dadhi/FastExpressionCompiler/sessions/9613f5f4-79a9-4a47-ad46-14c291909fb4 Co-authored-by: dadhi <39516+dadhi@users.noreply.github.com>

Copilot AI requested a review from dadhi April 14, 2026 06:18

Copilot finished work on behalf of dadhi April 14, 2026 06:18

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IL emit hack: direct token writes via UnsafeAccessorType (NET10+), caller-hint overloads, and benchmark harness#515

IL emit hack: direct token writes via UnsafeAccessorType (NET10+), caller-hint overloads, and benchmark harness#515
Copilot wants to merge 4 commits intocopilot/use-unsafeaccess-net8-and-net10from
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What the hack does

Changes

ILGeneratorTools (FastExpressionCompiler.cs)

DynamicMethodHacks

Fallbacks (correctness)

Benchmark & tests

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Copilot AI commented Apr 13, 2026 •

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`ILGeneratorTools` (`FastExpressionCompiler.cs`)

`DynamicMethodHacks`