Fix issues related to WebAssembly interface dispatch: (#5735)

1. Don't add a vtable offset to interface slot numbers
2. Ensure values are loaded before applying conv to them to avoid loading too wide of a value (found when interface dispatch loads a uint16 and then converts to IntPtr)

2 files changed, 14 insertions, 19 deletions

diff --git a/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs b/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs
index f49035bde..c3ead694d 100644
--- a/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs
+++ b/src/ILCompiler.WebAssembly/src/CodeGen/ILToWebAssemblyImporter.cs
@@ -2015,26 +2015,12 @@ namespace Internal.IL
         private void ImportConvert(WellKnownType wellKnownType, bool checkOverflow, bool unsigned)
         {
             StackEntry value = _stack.Pop();
-            LLVMValueRef convertedValue;
             TypeDesc destType = GetWellKnownType(wellKnownType);
 
-            //conv.u for a pointer should change to a int8*
-            if (wellKnownType == WellKnownType.UIntPtr)
-            {
-                if (value.Kind == StackValueKind.Int32)
-                {
-                    convertedValue = LLVM.BuildIntToPtr(_builder, value.ValueAsInt32(_builder, false), LLVM.PointerType(LLVM.Int8Type(), 0), "conv.u");
-                }
-                else
-                {
-                    convertedValue = value.ValueAsType(destType, _builder);
-                }
-            }
-            else
-            {
-                convertedValue = value.ValueAsType(destType, _builder);
-            }
-            PushExpression(GetStackValueKind(destType), "conv", convertedValue, destType);
+            // Load the value and then convert it instead of using ValueAsType to avoid loading the incorrect size
+            LLVMValueRef loadedValue = value.ValueAsType(value.Type, _builder);
+            LLVMValueRef converted = CastIfNecessary(loadedValue, GetLLVMTypeForTypeDesc(destType));
+            PushExpression(GetStackValueKind(destType), "conv", converted, destType);
         }
 
         private void ImportUnaryOperation(ILOpcode opCode)
diff --git a/src/ILCompiler.WebAssembly/src/Compiler/DependencyAnalysis/WebAssemblyVTableSlotNode.cs b/src/ILCompiler.WebAssembly/src/Compiler/DependencyAnalysis/WebAssemblyVTableSlotNode.cs
index e48163267..c9924f68a 100644
--- a/src/ILCompiler.WebAssembly/src/Compiler/DependencyAnalysis/WebAssemblyVTableSlotNode.cs
+++ b/src/ILCompiler.WebAssembly/src/Compiler/DependencyAnalysis/WebAssemblyVTableSlotNode.cs
@@ -61,7 +61,16 @@ namespace ILCompiler.DependencyAnalysis
 
             if (!relocsOnly)
             {
-                var tableOffset = EETypeNode.GetVTableOffset(factory.Target.PointerSize) / factory.Target.PointerSize;
+                int tableOffset;
+                if (_targetMethod.OwningType.IsInterface)
+                {
+                    tableOffset = 0;
+                }
+                else
+                {
+                    tableOffset = EETypeNode.GetVTableOffset(factory.Target.PointerSize) / factory.Target.PointerSize;
+                }
+
                 objData.EmitInt(tableOffset + VirtualMethodSlotHelper.GetVirtualMethodSlot(factory, _targetMethod, _targetMethod.OwningType));
             }
             return objData.ToObjectData();