Change iftable to never be null

Simplifies code generation by removing a null check. The null case
is rare.

Ritzperf code size: 13107624 -> 13095336

Also addressed comments from previous CL.

Bug: 32577579

Test: test-art-host, run ritzperf both with CC

Change-Id: I2b31e800867112869d7f0643e16c08826296979e
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 4ab6065..6ec9c91 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -3802,12 +3802,9 @@
                                         iftable_offset,
                                         maybe_temp2_loc,
                                         kWithoutReadBarrier);
-      // Null iftable means it is empty and will always fail the check.
-      __ Cbz(temp, type_check_slow_path->GetEntryLabel());
-
-      // Loop through the iftable and check if any class matches.
+      // Iftable is never null.
       __ Ldr(WRegisterFrom(maybe_temp2_loc), HeapOperand(temp.W(), array_length_offset));
-
+      // Loop through the iftable and check if any class matches.
       vixl::aarch64::Label start_loop;
       __ Bind(&start_loop);
       __ Cbz(WRegisterFrom(maybe_temp2_loc), type_check_slow_path->GetEntryLabel());