[wasm][R2R] Fix Vector128 argument alignment in crossgen ArgIterator

src/coreclr/tools/Common/Compiler/CompilerTypeSystemContext.Wasm.cs

@@ -5,6 +5,8 @@
 
 using Internal.TypeSystem;
 
+using Debug = System.Diagnostics.Debug;
+
 namespace ILCompiler
 {
     public partial class CompilerTypeSystemContext
@@ -25,6 +27,11 @@ public partial class CompilerTypeSystemContext
         /// </summary>
         public void CacheV128Type(TypeDesc type)
         {
+            // All v128 types share the same wasm ABI (16-byte aligned), so any one round-trips the
+            // 'V' encoding identically; a smaller alignment would change raised signatures silently.
+            Debug.Assert(type is DefType defType && defType.InstanceFieldAlignment.AsInt == 16,
+                $"v128 type {type} must be 16-byte aligned to be interchangeable in raised signatures");
+
             _cachedV128Type ??= type;
         }
 

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCompilerContext.cs

@@ -311,7 +311,10 @@ public override ComputedInstanceFieldLayout ComputeInstanceLayout(DefType type,
                 {
                     ByteCountUnaligned = layoutFromSimilarIntrinsicVector.ByteCountUnaligned,
                     ByteCountAlignment = layoutFromMetadata.ByteCountAlignment,
-                    FieldAlignment = layoutFromMetadata.FieldAlignment,
+                    // On wasm Vector<T> is passed as a v128 and must share its 16-byte alignment.
+                    FieldAlignment = type.Context.Target.Architecture == TargetArchitecture.Wasm32
+                        ? layoutFromSimilarIntrinsicVector.FieldAlignment
+                        : layoutFromMetadata.FieldAlignment,
                     FieldSize = layoutFromSimilarIntrinsicVector.FieldSize,
                     Offsets = layoutFromMetadata.Offsets,
                     LayoutAbiStable = true,

src/coreclr/vm/methodtablebuilder.cpp

@@ -10700,6 +10700,18 @@ void MethodTableBuilder::CheckForSystemTypes()
 
                 return;
             }
+
+#ifdef TARGET_WASM
+            // System.Numerics.Vector<T> is a v128 value on wasm, so it needs the same 16-byte
+            // alignment as System.Runtime.Intrinsics.Vector128<T> above. Its metadata layout is
+            // already 16 bytes (two UInt64 fields), but those only give it 8-byte alignment,
+            // which disagrees with crossgen2 and the interpreter.
+            if ((strcmp(nameSpace, g_NumericsNS) == 0) && (strcmp(name, "Vector`1") == 0))
+            {
+                pClass->GetLayoutInfo()->SetAlignmentRequirement(16); // sizeof(v128)
+                return;
+            }
+#endif // TARGET_WASM
         }
 
         if (g_pNullableClass != NULL)