[clr-interp] Fix more issues implicit conversions (#121319)

- When boxing to a floating point value, ensure that the stack value has
the correct type
- When boxing to a native int or uint, if the stack value is I4 and
we're on a 64bit platform, sign-extend the I4 before boxing
- When stack's merge convert to the target stack type instead of blindly
copying.

---------

Co-authored-by: Copilot <[email protected]>

Author: davidwrighton

src/coreclr/interpreter/compiler.cpp

@@ -567,8 +567,43 @@ void InterpCompiler::EmitBBEndVarMoves(InterpBasicBlock *pTargetBB)
         int dVar = pTargetBB->pStackState[i].var;
         if (sVar != dVar)
         {
-            InterpType interpType = m_pVars[sVar].interpType;
-            int32_t movOp = InterpGetMovForType(interpType, false);
+            InterpType interpType = g_interpTypeFromStackType[m_pStackBase[i].GetStackType()];
+            InterpType interpDestType = g_interpTypeFromStackType[pTargetBB->pStackState[i].GetStackType()];
+            int32_t movOp;
+            if (interpType != interpDestType)
+            {
+                if (interpType == InterpTypeR4 && interpDestType == InterpTypeR8)
+                {
+                    movOp = INTOP_CONV_R8_R4;
+                }
+                else if (interpType == InterpTypeR8 && interpDestType == InterpTypeR4)
+                {
+                    movOp = INTOP_CONV_R4_R8;
+                }
+                else if (interpType == InterpTypeI && interpDestType == InterpTypeByRef)
+                {
+                    movOp = InterpGetMovForType(interpDestType, false);
+                }
+#ifdef TARGET_64BIT
+                // nint and int32 can be used interchangeably. Add implicit conversions.
+                else if (interpType == InterpTypeI4 && interpDestType == InterpTypeI8)
+                {
+                    movOp = INTOP_CONV_I8_I4;
+                }
+                else if (interpType == InterpTypeI8 && interpDestType == InterpTypeI4)
+                {
+                    movOp = InterpGetMovForType(interpDestType, false);
+                }
+#endif // TARGET_64BIT
+                else
+                {
+                    BADCODE("Incompatible types on stack between basic blocks");
+                }
+            }
+            else
+            {
+                movOp = InterpGetMovForType(interpType, false);
+            }
 
             AddIns(movOp);
             m_pLastNewIns->SetSVar(sVar);
@@ -7989,6 +8024,26 @@ void InterpCompiler::GenerateCode(CORINFO_METHOD_INFO* methodInfo)
 
                 if (m_compHnd->isValueClass(resolvedToken.hClass))
                 {
+                    CorInfoType asCorInfoType = m_compHnd->asCorInfoType(m_compHnd->getTypeForBox(resolvedToken.hClass));
+                    if (asCorInfoType == CORINFO_TYPE_FLOAT && m_pStackPointer[-1].GetStackType() == StackTypeR8)
+                    {
+                        EmitConv(m_pStackPointer - 1, StackTypeR4, INTOP_CONV_R4_R8);
+                    }
+                    else if (asCorInfoType == CORINFO_TYPE_DOUBLE && m_pStackPointer[-1].GetStackType() == StackTypeR4)
+                    {
+                        EmitConv(m_pStackPointer - 1, StackTypeR8, INTOP_CONV_R8_R4);
+                    }
+#ifdef TARGET_64BIT
+                    // nint and int32 can be used interchangeably. Add implicit conversions.
+                    else if (asCorInfoType == CORINFO_TYPE_NATIVEINT && m_pStackPointer[-1].GetStackType() == StackTypeI4)
+                    {
+                        EmitConv(m_pStackPointer - 1, StackTypeI8, INTOP_CONV_I8_I4);
+                    }
+                    else if (asCorInfoType == CORINFO_TYPE_NATIVEUINT && m_pStackPointer[-1].GetStackType() == StackTypeI4)
+                    {
+                        EmitConv(m_pStackPointer - 1, StackTypeI8, INTOP_CONV_I8_U4);
+                    }
+#endif // TARGET_64BIT
                     CORINFO_GENERICHANDLE_RESULT embedInfo;
                     m_compHnd->embedGenericHandle(&resolvedToken, false, m_methodInfo->ftn, &embedInfo);
                     m_pStackPointer -= 1;