Resolve ILVerify errors — adjust codegen (551 → 56 errors) by T-Gro · Pull Request #19372 · dotnet/fsharp

T-Gro · 2026-03-02T09:24:17Z

For a long time, the F# compiler was producing IL code that did not pass ILVerify. This time ends now :)

This PR fixes the vast majority of ILVerify errors across FSharp.Compiler.Service and FSharp.Core (551 → 56), by adjusting IL codegen in 5 targeted waves. The 56 remaining errors are all native pointer / unmanaged memory operations (NativePtr, RawByteMemory, castToString, retype) — inherently unverifiable by design.

Each codegen change includes benchmarks comparing code compiled by the local (patched) compiler vs the SDK compiler, confirming no runtime regressions.

Wave 1: Specialized `stelem`/`ldelem` for primitive types (`ilwrite.fs`)

Problem: The IL writer emitted stelem <TypeToken> / ldelem <TypeToken> for primitive array element types (bool, char, int32, etc.). ILVerify's type verification treats the loaded/stored values as the verification type of the token, which for small integers like bool and char differs from the stack representation. This causes StackUnexpected errors.

Fix: Map primitive ILTypes to their corresponding ILBasicType and emit specialized instructions (stelem.i4, ldelem.u2, etc.) which have well-defined verification semantics. This is the largest single wave — it eliminated errors across the entire compiler and FSharp.Core.

Files: src/Compiler/AbstractIL/ilwrite.fs

Wave 2a: `callvirt` → `call` on value types (`IlxGen.fs`)

Problem: The codegen emitted callvirt for method calls on unboxed value types (e.g., struct.GetHashCode()). ECMA-335 requires call or constrained callvirt for value type methods — plain callvirt is invalid on an unboxed value type receiver.

Fix: Guard callvirt emission with boxity <> AsValue in both GenApp and GenILCall, falling through to call for value types.

Files: src/Compiler/CodeGen/IlxGen.fs

Wave 2b: `castclass` at interface join points (`IlxGen.fs`)

Problem: When a match expression returns an interface type and branches produce different concrete classes, the IL verifier computes the LUB of the concrete types at the join point as System.Object instead of the interface. This causes StackUnexpected at the consumer of the join point result.

Fix: Introduce a CastThenBr sequel that emits castclass to the interface type before branching to the join label. Applied only when the result type is an interface and all branches produce reference types.

Files: src/Compiler/CodeGen/IlxGen.fs

Wave 3: Filter → catch inside finally/fault handlers (`IlxGen.fs`)

Problem: try/with using a when guard inside a finally block emitted a filter block nested inside the finally handler. ILVerify (incorrectly) computes the entry stack for such a filter as empty (the finally entry) instead of having the exception object on stack, causing StackUnderflow. See dotnet/runtime#112406.

Fix: Track insideFinallyOrFaultHandler in the codegen environment and suppress filter block emission inside finally/fault handlers, falling back to a catch-based pattern instead.

Files: src/Compiler/CodeGen/IlxGen.fs

Wave 4: Witness field alignment in state machine structs (`IlxGen.fs`)

Problem: GenStructStateMachine initialized closure fields by zipping cloFreeVars with ilCloAllFreeVars. When SRTP witnesses are present, ilCloAllFreeVars has witness fields prepended, so the zip was misaligned — witness fields got regular free var values and vice versa. This produced type mismatches (StackUnexpected) in task { let! ... and! ... } expressions.

Fix: Initialize witness fields separately (first N entries of ilCloAllFreeVars), then zip the remaining entries with cloFreeVars.

Files: src/Compiler/CodeGen/IlxGen.fs

ILVerify error count

Baseline	Before	After
FSharp.Compiler.Service Debug net10.0	73	11
FSharp.Compiler.Service Debug netstandard2.0	98	11
FSharp.Compiler.Service Release net10.0	99	12
FSharp.Compiler.Service Release netstandard2.0	125	12
FSharp.Core Debug netstandard2.0	42	5
FSharp.Core Debug netstandard2.1	42	5
FSharp.Core Release netstandard2.0	36	0 ✅
FSharp.Core Release netstandard2.1	36	0 ✅
Total	551	56

Remaining 56 errors are all Unmanaged pointers are not a verifiable type / StackUnexpected on retype/castToString/castclassPrim/iscastPrim/notnullPrim — intrinsically unverifiable operations.

Benchmark results (LocalCompiler = this PR, SdkCompiler = baseline)

No regression: stelem/ldelem (0.99–1.03, within noise), task CEs, callvirt→call (StructToString, StructEquals, StructInDictionary)
Slight improvement: callvirt→call on GetHashCode (0.93–0.96), CastThenBr on interface match (0.88–0.95), filter→catch on exception paths (0.93–0.96)
Slight regression: filter→catch on no-exception path (1.06)

Full BenchmarkDotNet output


BenchmarkDotNet v0.13.10, macOS 26.2 (25C56) [Darwin 25.2.0]
Apple M3 Max, 1 CPU, 16 logical and 16 physical cores
.NET SDK 10.0.101
  [Host]        : .NET 10.0.1 (10.0.125.57005), Arm64 RyuJIT AdvSIMD DEBUG
  LocalCompiler : .NET 10.0.2 (10.0.225.61305), Arm64 RyuJIT AdvSIMD
  SdkCompiler   : .NET 10.0.2 (10.0.225.61305), Arm64 RyuJIT AdvSIMD

Arguments=/p:BUILDING_USING_DOTNET=true

Type	Method	Job	Mean	Error	StdDev	Median	P95	Ratio	RatioSD	Gen0	Gen1	Allocated	Alloc Ratio
CallVirtOnValueTypeBenchmark	StructGetHashCode	LocalCompiler	3,011.739 ns	4.1497 ns	3.8816 ns	3,011.152 ns	3,018.224 ns	1.00	0.00	-	-	-	NA
CallVirtOnValueTypeBenchmark	StructGetHashCode	SdkCompiler	3,020.885 ns	3.4751 ns	2.9019 ns	3,021.219 ns	3,024.821 ns	1.00	0.00	-	-	-	NA

CastThenBrBenchmark	MatchReturningInterface_NoAlloc	LocalCompiler	23,985.794 ns	475.2417 ns	794.0221 ns	23,652.795 ns	25,443.705 ns	0.88	0.06	-	-	-	NA
CastThenBrBenchmark	MatchReturningInterface_NoAlloc	SdkCompiler	27,398.117 ns	543.5979 ns	1,432.0542 ns	27,033.290 ns	30,303.813 ns	1.00	0.00	-	-	-	NA

FilterInFinallyBenchmark	TryWithInFinally_NoException	LocalCompiler	555.539 ns	10.4836 ns	17.2249 ns	548.821 ns	586.716 ns	1.06	0.04	-	-	-	NA
FilterInFinallyBenchmark	TryWithInFinally_NoException	SdkCompiler	530.672 ns	1.7119 ns	1.4295 ns	530.475 ns	533.055 ns	1.00	0.00	-	-	-	NA

StelemLdelemBenchmark	BoolArrayReadWrite	LocalCompiler	3,589.626 ns	24.9488 ns	20.8334 ns	3,587.869 ns	3,625.366 ns	1.02	0.01	-	-	-	NA
StelemLdelemBenchmark	BoolArrayReadWrite	SdkCompiler	3,513.090 ns	40.1561 ns	37.5620 ns	3,536.126 ns	3,547.690 ns	1.00	0.00	-	-	-	NA

TaskMergeSourcesBenchmark	TaskLetBangAndBang	LocalCompiler	14.754 ns	0.2272 ns	0.2125 ns	14.692 ns	15.123 ns	1.00	0.02	0.0004	-	72 B	1.00
TaskMergeSourcesBenchmark	TaskLetBangAndBang	SdkCompiler	14.751 ns	0.0665 ns	0.0589 ns	14.737 ns	14.860 ns	1.00	0.00	0.0004	-	72 B	1.00

CallVirtOnValueTypeBenchmark	StructToString	LocalCompiler	6,550.059 ns	30.8829 ns	28.8879 ns	6,552.014 ns	6,596.813 ns	1.00	0.00	0.1678	-	27960 B	1.00
CallVirtOnValueTypeBenchmark	StructToString	SdkCompiler	6,522.629 ns	22.4117 ns	17.4976 ns	6,524.147 ns	6,548.854 ns	1.00	0.00	0.1678	-	27960 B	1.00

CastThenBrBenchmark	MatchReturningInterface_Alloc	LocalCompiler	57,340.381 ns	566.1241 ns	501.8542 ns	57,160.351 ns	58,333.448 ns	1.02	0.01	1.5869	-	266456 B	1.00
CastThenBrBenchmark	MatchReturningInterface_Alloc	SdkCompiler	56,407.777 ns	807.8752 ns	755.6869 ns	56,003.489 ns	57,572.996 ns	1.00	0.00	1.5869	-	266456 B	1.00

FilterInFinallyBenchmark	TryWithInFinally_WithException	LocalCompiler	2,140,943.877 ns	42,143.2213 ns	51,755.6605 ns	2,130,150.148 ns	2,226,091.349 ns	0.93	0.07	-	-	216000 B	1.00
FilterInFinallyBenchmark	TryWithInFinally_WithException	SdkCompiler	2,262,674.964 ns	56,794.0958 ns	151,594.9387 ns	2,201,999.594 ns	2,728,839.813 ns	1.00	0.00	-	-	216003 B	1.00

StelemLdelemBenchmark	IntArrayReadWrite	LocalCompiler	2,884.971 ns	9.4347 ns	8.3636 ns	2,885.090 ns	2,896.610 ns	1.03	0.00	-	-	-	NA
StelemLdelemBenchmark	IntArrayReadWrite	SdkCompiler	2,812.112 ns	6.3549 ns	5.3067 ns	2,811.917 ns	2,820.260 ns	1.00	0.00	-	-	-	NA

TaskMergeSourcesBenchmark	TaskLetBangAndBang3	LocalCompiler	27.341 ns	0.3246 ns	0.2711 ns	27.374 ns	27.714 ns	1.01	0.01	0.0009	-	152 B	1.00
TaskMergeSourcesBenchmark	TaskLetBangAndBang3	SdkCompiler	27.020 ns	0.2093 ns	0.1748 ns	27.045 ns	27.238 ns	1.00	0.00	0.0009	-	152 B	1.00

CallVirtOnValueTypeBenchmark	StructEquals	LocalCompiler	29,573.711 ns	220.8120 ns	206.5476 ns	29,562.723 ns	29,922.468 ns	1.01	0.02	1.4343	-	239976 B	1.00
CallVirtOnValueTypeBenchmark	StructEquals	SdkCompiler	29,420.301 ns	390.6764 ns	365.4390 ns	29,608.037 ns	29,790.980 ns	1.00	0.00	1.4343	-	239976 B	1.00

CastThenBrBenchmark	MatchReturningIComparable	LocalCompiler	91,689.908 ns	369.9182 ns	308.8985 ns	91,709.345 ns	92,134.706 ns	0.95	0.04	0.8545	-	159264 B	1.00
CastThenBrBenchmark	MatchReturningIComparable	SdkCompiler	95,445.088 ns	1,708.9753 ns	3,413.0083 ns	93,995.697 ns	103,541.611 ns	1.00	0.00	0.8545	-	159264 B	1.00

FilterInFinallyBenchmark	TryWithInFinally_GuardHit	LocalCompiler	1,972,895.145 ns	8,926.4190 ns	7,453.9641 ns	1,969,982.098 ns	1,984,866.016 ns	0.96	0.01	-	-	224000 B	1.00
FilterInFinallyBenchmark	TryWithInFinally_GuardHit	SdkCompiler	2,068,823.482 ns	26,346.7064 ns	24,644.7255 ns	2,058,629.232 ns	2,102,062.206 ns	1.00	0.00	-	-	224001 B	1.00

StelemLdelemBenchmark	CharArrayReadWrite	LocalCompiler	3,837.618 ns	7.9594 ns	6.6464 ns	3,834.811 ns	3,848.598 ns	0.99	0.00	-	-	-	NA
StelemLdelemBenchmark	CharArrayReadWrite	SdkCompiler	3,884.815 ns	19.1506 ns	15.9916 ns	3,878.658 ns	3,914.045 ns	1.00	0.00	-	-	-	NA

TaskMergeSourcesBenchmark	TaskLetBangSequential	LocalCompiler	5.368 ns	0.1307 ns	0.1790 ns	5.324 ns	5.703 ns	1.00	0.06	-	-	-	NA
TaskMergeSourcesBenchmark	TaskLetBangSequential	SdkCompiler	5.382 ns	0.1341 ns	0.1435 ns	5.359 ns	5.664 ns	1.00	0.00	-	-	-	NA

CallVirtOnValueTypeBenchmark	StructInDictionary	LocalCompiler	12,207.604 ns	142.8089 ns	133.5836 ns	12,157.128 ns	12,412.242 ns	1.00	0.01	0.6866	0.0916	111648 B	1.00
CallVirtOnValueTypeBenchmark	StructInDictionary	SdkCompiler	12,189.143 ns	148.7887 ns	165.3783 ns	12,107.841 ns	12,486.912 ns	1.00	0.00	0.6866	0.0916	111648 B	1.00

FilterInFinallyBenchmark	SimpleTryFinally	LocalCompiler	530.156 ns	1.2822 ns	1.0707 ns	530.444 ns	531.379 ns	0.96	0.01	-	-	-	NA
FilterInFinallyBenchmark	SimpleTryFinally	SdkCompiler	552.759 ns	10.7679 ns	8.9917 ns	548.853 ns	569.225 ns	1.00	0.00	-	-	-	NA

StelemLdelemBenchmark	SByteArrayReadWrite	LocalCompiler	5,512.868 ns	28.2968 ns	26.4689 ns	5,510.768 ns	5,560.457 ns	0.99	0.01	-	-	-	NA
StelemLdelemBenchmark	SByteArrayReadWrite	SdkCompiler	5,576.221 ns	76.5248 ns	63.9016 ns	5,575.136 ns	5,679.119 ns	1.00	0.00	-	-	-	NA

TaskMergeSourcesBenchmark	TaskSimple	LocalCompiler	6.829 ns	0.0918 ns	0.0859 ns	6.832 ns	6.976 ns	1.01	0.02	0.0004	-	72 B	1.00
TaskMergeSourcesBenchmark	TaskSimple	SdkCompiler	6.746 ns	0.1331 ns	0.1112 ns	6.704 ns	6.943 ns	1.00	0.00	0.0004	-	72 B	1.00

CallVirtOnValueTypeBenchmark	IntGetHashCode	LocalCompiler	2,504.634 ns	6.6625 ns	5.9061 ns	2,503.363 ns	2,513.041 ns	0.93	0.00	-	-	-	NA
CallVirtOnValueTypeBenchmark	IntGetHashCode	SdkCompiler	2,692.462 ns	6.0291 ns	5.3446 ns	2,692.454 ns	2,700.421 ns	1.00	0.00	-	-	-	NA

StelemLdelemBenchmark	ByteArrayReadWrite	LocalCompiler	3,827.056 ns	20.1288 ns	16.8085 ns	3,833.095 ns	3,837.618 ns	1.02	0.00	-	-	-	NA
StelemLdelemBenchmark	ByteArrayReadWrite	SdkCompiler	3,742.817 ns	8.5823 ns	7.1666 ns	3,745.259 ns	3,752.045 ns	1.00	0.00	-	-	-	NA

CallVirtOnValueTypeBenchmark	DateTimeGetHashCode	LocalCompiler	2,629.997 ns	38.8126 ns	34.4064 ns	2,637.633 ns	2,670.062 ns	0.96	0.01	-	-	-	NA
CallVirtOnValueTypeBenchmark	DateTimeGetHashCode	SdkCompiler	2,724.887 ns	10.5121 ns	8.7781 ns	2,720.738 ns	2,741.800 ns	1.00	0.00	-	-	-	NA

StelemLdelemBenchmark	IntArrayFilterToArray	LocalCompiler	7,796.051 ns	23.8529 ns	21.1450 ns	7,796.818 ns	7,825.524 ns	0.99	0.01	0.1221	-	21296 B	1.00
StelemLdelemBenchmark	IntArrayFilterToArray	SdkCompiler	7,882.273 ns	125.4244 ns	111.1855 ns	7,827.736 ns	8,067.406 ns	1.00	0.00	0.1221	-	21296 B	1.00

StelemLdelemBenchmark	BoolArrayCountTrue	LocalCompiler	2,800.847 ns	17.0188 ns	15.0868 ns	2,796.306 ns	2,828.988 ns	1.00	0.01	-	-	-	NA
StelemLdelemBenchmark	BoolArrayCountTrue	SdkCompiler	2,809.914 ns	22.2283 ns	20.7924 ns	2,801.633 ns	2,849.625 ns	1.00	0.00	-	-	-	NA

When emitting IL for I_stelem_any and I_ldelem_any with primitive element types (bool, byte, char, int16, int32, etc.), emit the specialized instructions (stelem.i1, stelem.i4, ldelem.u1, etc.) instead of the generic stelem <T> / ldelem <T> form. This matches C# compiler behavior and eliminates 306 ILVerify StackUnexpected errors caused by asymmetric verification type handling in ILVerify (ECMA-335 §I.8.7). ILVerify baseline changes: - FSharp.Core: 32 → 20 errors (Release), 37 → 25 (Debug) - FSharp.Compiler.Service: 125 → 18 (Release ns2.0), 99 → 18 (net10) 98 → 16 (Debug ns2.0), 73 → 16 (Debug net10) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ange struct GetHashCode - HashMultiMap: Add explicit :> IDictionary<_,_> upcasts in both branches of the if/else expressions for firstEntries and rest fields. This causes the F# compiler to emit castclass at the join point, which ILVerify needs to see the correct interface type on the stack instead of computing the LUB of ConcurrentDictionary and Dictionary as System.Object. - range.fs: Change o.GetHashCode() to (box o).GetHashCode() in the Range struct IEqualityComparer. Range is a struct, and callvirt on a value type without a constrained. prefix is flagged by ILVerify as CallVirtOnValueType. Boxing first makes the callvirt valid on the boxed reference type. Together these eliminate 5 ILVerify baseline entries (2 HashMultiMap + 1 AssemblyResolveHandler + 1 FSharpChecker + 1 CallVirtOnValueType). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…st and Range struct GetHashCode" This reverts commit 4614ffe.

… casts Two codegen fixes to eliminate ILVerify errors: 1. CallVirtOnValueType: In GenApp, prevent emitting callvirt when the declaring type is a value type (boxity = AsValue). For value types, callvirt without constrained. prefix is invalid per ECMA-335. This also applies as a safety net in GenILCall. 2. Interface join point casts: Add CastThenBr sequel that emits castclass before branching at match/if-else join points when the result type is an interface. Without this, ILVerify computes the LUB of different concrete class types as System.Object instead of the expected interface type. Only applied when all branches produce reference types (not value types or unit). Eliminates 5 ILVerify baseline entries per configuration: - HashMultiMap StackUnexpected x2 (IDictionary join) - AssemblyResolveHandler StackUnexpected (IDisposable join) - FSharpChecker StackUnexpected (IBackgroundCompiler join) - comparer@607 CallVirtOnValueType (Range.GetHashCode) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ILVerify has a bug where a filter nested inside a finally handler gets its entry stack computed incorrectly (as empty instead of [exception_object]). This happens because ILVerify's FindEnclosingExceptionRegions picks HandlerIndex (the enclosing finally) instead of FilterIndex when both are set, then uses the finally's Kind to determine stack state. The fix adds insideFinallyOrFaultHandler tracking to IlxGenEnv. When inside a finally handler, GenTryWith emits catch blocks instead of filter blocks. Semantically identical for catch-all patterns (filter always returns 1 == catch Exception). Eliminates the DoWithColor StackUnderflow error: - FCS Release: 13 -> 12 errors per config - FCS Debug: 11 -> 10 errors per config (to be verified by CI) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

GenStructStateMachine zipped cloFreeVars (regular free vars only) with ilCloAllFreeVars (witness fields + regular fields). When witness fields were present (in $W methods), the zip was misaligned: regular var values were stored into witness fields and vice versa. The fix initializes witness fields separately first, then skips them when zipping with regular free vars. This was a genuine codegen bug affecting all MergeSources$W methods in FSharp.Core task computation expressions. The $W state machine struct had both witness function fields (getAwaiter, getResult, get_IsCompleted) and regular value fields (computation, task), but the initialization code stored task values into witness fields due to the array offset mismatch. Eliminates all 20 FSharp.Core Release ILVerify errors and all 20 MergeSources$W errors from Debug baselines. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

BDN benchmarks for each IL codegen change: - StelemLdelem: primitive array read/write (ldelem.u1, stelem.i4, etc.) - CallVirtOnValueType: struct GetHashCode/ToString/Equals (call vs callvirt) - CastThenBr: match returning interface types (castclass at join points) - FilterInFinally: try/with inside finally (catch vs filter) Results: no regressions. callvirt→call shows 4-7% improvement for struct method calls. All other changes performance-neutral. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-03-02T09:30:22Z

❗ Release notes required

✅ Found changes and release notes in following paths:

Change path Release notes path Description

src/Compiler docs/release-notes/.FSharp.Compiler.Service/10.0.300.md

- TailCall 06: Update IL offsets (IL_0040→IL_0034) due to stelem.i4 being shorter - ILVerify Debug baselines: Fix set_Item offset (0x1F→0x25), normalize pointerToNativeInt - ILVerify script: Handle empty baseline matching empty output (FSharp.Core Release) - StructDU net472 baseline: callvirt→call on value type ToString() - Trimming check: Update expected FSharp.Core.dll size (311296→311808) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

vzarytovskii · 2026-03-02T15:34:04Z

Nice, finally!

vzarytovskii · 2026-03-02T15:35:59Z

IIRC (I don't have data to support that, only old discussions I had with Don and Kevin), exception filters resluted in some worse runtime perf on old runtimes, not sure if we care or care to confrim/deny that.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

T-Gro · 2026-03-02T16:15:53Z

It was for mono.
The F.C.S itself is using them in the last 1-2 stable versions without complaints.

(i.e. no reported problems on the environments where people run the compiler/SDK. Which of course does not mean all environments where the compiled code can run)

UPDATE: The filter blocks are only default for the compiler itself, it is a compiler switch. Changing it to be come default for all users is a different story, not done here.

github-project-automation bot added this to F# Compiler and Tooling Mar 2, 2026

github-project-automation bot moved this to New in F# Compiler and Tooling Mar 2, 2026

T-Gro and others added 9 commits March 2, 2026 10:27

Revert "Fix source-level ILVerify errors: HashMultiMap interface upca…

e91c70b

…st and Range struct GetHashCode" This reverts commit 4614ffe.

remove superflous comments

6c0f56b

Add release notes for ILVerify codegen fixes

8d4513d

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

T-Gro force-pushed the eng/tackle-ilverify-errors branch from 6cf2d68 to 8d4513d Compare March 2, 2026 09:29

T-Gro changed the title ~~Resolve ilverify errors - adjust codegen~~ Resolve ILVerify errors — adjust codegen (551 → 56 errors) Mar 2, 2026

T-Gro and others added 2 commits March 2, 2026 10:43

fantomas

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github-project-automation bot moved this from New to In Progress in F# Compiler and Tooling Mar 2, 2026

Fix ILVerify empty baseline check: filter to error lines only

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Merge branch 'main' into eng/tackle-ilverify-errors

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T-Gro marked this pull request as ready for review March 2, 2026 16:55

T-Gro requested a review from a team as a code owner March 2, 2026 16:55

T-Gro added 2 commits March 3, 2026 11:17

Merge branch 'main' into eng/tackle-ilverify-errors

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Merge branch 'main' into eng/tackle-ilverify-errors

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Resolve ILVerify errors — adjust codegen (551 → 56 errors)#19372

Resolve ILVerify errors — adjust codegen (551 → 56 errors)#19372
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Wave 1: Specialized stelem/ldelem for primitive types (ilwrite.fs)

Wave 2a: callvirt → call on value types (IlxGen.fs)

Wave 2b: castclass at interface join points (IlxGen.fs)

Wave 3: Filter → catch inside finally/fault handlers (IlxGen.fs)

Wave 4: Witness field alignment in state machine structs (IlxGen.fs)

ILVerify error count

Benchmark results (LocalCompiler = this PR, SdkCompiler = baseline)

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T-Gro commented Mar 2, 2026 •

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Wave 1: Specialized `stelem`/`ldelem` for primitive types (`ilwrite.fs`)

Wave 2a: `callvirt` → `call` on value types (`IlxGen.fs`)

Wave 2b: `castclass` at interface join points (`IlxGen.fs`)

Wave 3: Filter → catch inside finally/fault handlers (`IlxGen.fs`)

Wave 4: Witness field alignment in state machine structs (`IlxGen.fs`)

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