[mono] Added null-checks for LDFLDA on pointers. (#77827)

* Added a null check for LDFLDA with pointers.

* Reenabled LDFLDA pointer null-check runtime test for mono.

* Added null check for LDFLDA in Mono interpreter.

* [mono][interp] LDFLDA fix for null pointers now keeps more optimizations intact.

Author: jandupej

src/mono/mono/mini/interp/transform.c

@@ -6034,12 +6034,12 @@ generate_code (TransformData *td, MonoMethod *method, MonoMethodHeader *header,
 					/* TODO: metadata-update: implement me. If it's an added field, emit a call to the helper method instead of MINT_LDFLDA_UNSAFE */
 					g_assert (!m_field_is_from_update (field));
 					int foffset = m_class_is_valuetype (klass) ? m_field_get_offset (field) - MONO_ABI_SIZEOF (MonoObject) : m_field_get_offset (field);
-					if (td->sp->type == STACK_TYPE_O) {
+					if (td->sp->type == STACK_TYPE_O || td->sp->type == STACK_TYPE_I) {
 						interp_add_ins (td, MINT_LDFLDA);
 						td->last_ins->data [0] = GINT_TO_UINT16 (foffset);
 					} else {
 						int sp_type = td->sp->type;
-						g_assert (sp_type == STACK_TYPE_MP || sp_type == STACK_TYPE_I);
+						g_assert (sp_type == STACK_TYPE_MP);
 						if (foffset) {
 							interp_add_ins (td, MINT_LDFLDA_UNSAFE);
 							td->last_ins->data [0] = GINT_TO_UINT16 (foffset);

src/mono/mono/mini/method-to-ir.c

@@ -10007,7 +10007,7 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 				}
 
 				if (il_op == MONO_CEE_LDFLDA) {
-					if (sp [0]->type == STACK_OBJ) {
+					if (sp [0]->type == STACK_OBJ || sp [0]->type == STACK_PTR) {
 						MONO_EMIT_NEW_BIALU_IMM (cfg, OP_COMPARE_IMM, -1, sp [0]->dreg, 0);
 						MONO_EMIT_NEW_COND_EXC (cfg, EQ, "NullReferenceException");
 					}

src/tests/issues.targets

@@ -1478,9 +1478,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/GitHub_15291/GitHub_15291/**">
             <Issue>Doesn't pass after LLVM AOT compilation.</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/JitBlue/Runtime_77640/Runtime_77640/**">
-            <Issue>https://github.com/dotnet/runtime/issues/77647</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/JIT/Regression/CLR-x86-JIT/V1-M09.5-PDC/b16928/b16928/**">
             <Issue>Doesn't pass after LLVM AOT compilation.</Issue>
         </ExcludeList>