Fix a bug in OSR-entry guard checking

If we had to guard on the type of an object but the variable
ended up being undefined, we treated that as a guard failure
(not sure why).

Fixing that exposed another issue: if we guard that an object
is an int, we will try to unbox it if necessary.  If the variable
wasn't defined, then we will try to unbox some garbage memory.
Use the new handlePotentiallyUndefined to deal with that.

src/codegen/irgen.cpp

@@ -484,14 +484,26 @@ static void emitBBs(IRGenState* irstate, const char* bb_type, GuardList& out_gua
                             return type_check;
                         }
                     },
-                    [guard_val](IREmitter& emitter) { return getConstantInt(0, g.i1); });
+                    [guard_val](IREmitter& emitter) { return guard_val ? guard_val : getConstantInt(1, g.i1); });
 
                 if (speculated_class == int_cls) {
-                    v = unbox_emitter->getBuilder()->CreateCall(g.funcs.unboxInt, from_arg);
-                    (new ConcreteCompilerVariable(BOXED_INT, from_arg, true))->decvref(*unbox_emitter);
+                    v = handlePotentiallyUndefined(
+                        is_defined_var, INT->llvmType(), osr_unbox_block_end, *unbox_emitter, true,
+                        [from_arg](IREmitter& emitter) {
+                            auto v = emitter.getBuilder()->CreateCall(g.funcs.unboxInt, from_arg);
+                            (new ConcreteCompilerVariable(BOXED_INT, from_arg, true))->decvref(emitter);
+                            return v;
+                        },
+                        [](IREmitter& emitter) { return llvm::UndefValue::get(INT->llvmType()); });
                 } else if (speculated_class == float_cls) {
-                    v = unbox_emitter->getBuilder()->CreateCall(g.funcs.unboxFloat, from_arg);
-                    (new ConcreteCompilerVariable(BOXED_FLOAT, from_arg, true))->decvref(*unbox_emitter);
+                    v = handlePotentiallyUndefined(
+                        is_defined_var, FLOAT->llvmType(), osr_unbox_block_end, *unbox_emitter, true,
+                        [from_arg](IREmitter& emitter) {
+                            auto v = emitter.getBuilder()->CreateCall(g.funcs.unboxFloat, from_arg);
+                            (new ConcreteCompilerVariable(BOXED_FLOAT, from_arg, true))->decvref(emitter);
+                            return v;
+                        },
+                        [](IREmitter& emitter) { return llvm::UndefValue::get(FLOAT->llvmType()); });
                 } else {
                     assert(phi_type == typeFromClass(speculated_class));
                     v = from_arg;