From 7e76ec5cbe232020cd5e3d872ac9c3b381f96dd1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Strehovsk=C3=BD?=
 <MichalStrehovsky@users.noreply.github.com>
Date: Fri, 16 Oct 2026 17:05:34 +0900
Subject: [PATCH 1/2] Require matching WASM function types when folding method
 bodies

Identical bodies can have different WASM function types when parameters
are unused. An address-taken method's jump stub forwards its parameters
to the folded body, producing invalid WASM if their signatures differ.

Compare lowered function types before folding on WASM. This accounts for
hidden ABI parameters and leaves other architectures unchanged.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: a6f3a617-acae-4f4f-95d3-20b2a0bac43c
---
 .../ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs  | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs b/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs
index 94880f401f49b3..d4ec3067631241 100644
--- a/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs
+++ b/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs
@@ -7,6 +7,7 @@
 using ILCompiler.DependencyAnalysis;
 
 using Internal.IL.Stubs;
+using Internal.JitInterface;
 using Internal.TypeSystem;
 
 namespace ILCompiler
@@ -156,6 +157,11 @@ public bool Equals(MethodInternKey a, MethodInternKey b)
                     && a.Method.Method.GetTypicalMethodDefinition() != b.Method.Method.GetTypicalMethodDefinition())
                     return false;
 
+                // Identical WASM bodies can still have different types when some parameters are unused.
+                if (_factory.Target.IsWasm
+                    && !WasmLowering.GetSignature(a.Method.Method).FuncType.Equals(WasmLowering.GetSignature(b.Method.Method).FuncType))
+                    return false;
+
                 ObjectNode.ObjectData o1data = ((ObjectNode)a.Method).GetData(_factory, relocsOnly: false);
                 ObjectNode.ObjectData o2data = ((ObjectNode)b.Method).GetData(_factory, relocsOnly: false);
 

From d096062a9607b477100b1059d0298f4061f9f4eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Strehovsk=C3=BD?=
 <MichalStrehovsky@users.noreply.github.com>
Date: Mon, 19 Oct 2026 14:07:12 +0900
Subject: [PATCH 2/2] Feedback

---
 .../aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs b/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs
index 8263e0fa9a9d6c..8f216769b7911c 100644
--- a/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs
+++ b/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MethodBodyDeduplicator.cs
@@ -78,6 +78,9 @@ public MethodInternKey(IMethodBodyNode node, NodeFactory factory, Dictionary<ISy
                 var hashCode = default(HashCode);
                 hashCode.AddBytes(data.Data);
 
+                if (factory.Target.IsWasm)
+                    hashCode.Add(WasmLowering.GetSignature(node.Method).FuncType);
+
                 // Hash relocations consistently with MethodInternComparer.AreSame so that bodies that only differ
                 // in their relocation targets (e.g. instantiations over different struct state machines)
                 // don't all end up in the same bucket.