Fix generic argument access in filter funclets

src/coreclr/interpreter/compiler.cpp

@@ -5729,6 +5729,23 @@ void InterpCompiler::GenerateCode(CORINFO_METHOD_INFO* methodInfo)
             {
                 AddIns(INTOP_LOAD_EXCEPTION);
                 m_pLastNewIns->SetDVar(m_pCBB->clauseVarIndex);
+
+                // To allow filter clauses in generic methods to access the generic argument,
+                // we copy that argument variable from the parent frame to the filter's frame.
+                // The target variable offset is the same as the one in the parent frame.
+                if ((m_pCBB->clauseType == BBClauseFilter) && (m_paramArgIndex != -1))
+                {
+                    AddIns(INTOP_LOAD_FRAMEVAR);
+                    PushInterpType(InterpTypeI, NULL);
+                    m_pLastNewIns->SetDVar(m_pStackPointer[-1].var);
+
+                    m_pStackPointer--;
+                    int32_t opcode = GetLdindForType(m_pVars[m_paramArgIndex].interpType);
+                    AddIns(opcode);
+                    m_pLastNewIns->SetSVar(m_pStackPointer[0].var);
+                    m_pLastNewIns->SetDVar(m_paramArgIndex);
+                    m_pLastNewIns->data[0] = m_pVars[m_paramArgIndex].offset;
+                }
             }
         }
 

src/coreclr/interpreter/compiler.h

@@ -756,7 +756,7 @@ class InterpCompiler
     int32_t m_varsSize = 0;
     int32_t m_varsCapacity = 0;
     int32_t m_numILVars = 0;
-    int32_t m_paramArgIndex = 0; // Index of the type parameter argument in the m_pVars array.
+    int32_t m_paramArgIndex = -1; // Index of the type parameter argument in the m_pVars array.
     // For each catch or filter clause, we create a variable that holds the exception object.
     // This is the index of the first such variable.
     int32_t m_clauseVarsIndex = 0;