Support GVN for HLoadClass::LoadKind::kJitTableAddress.

Fixes performance regressions seen in eg Dhrystone.

Also add comment on why a class may not be found when sharpening.

Test: manual Dhrystone run, performance recovers
Test: ART_TEST_JIT=true test-art-host-run-test-jit
Change-Id: I8e879f1c390f83e8bc930f343beb7b4a41c2f190
diff --git a/compiler/optimizing/sharpening.cc b/compiler/optimizing/sharpening.cc
index bbbb1a1..91efb80 100644
--- a/compiler/optimizing/sharpening.cc
+++ b/compiler/optimizing/sharpening.cc
@@ -197,7 +197,9 @@
           // out which class loader to use.
           address = reinterpret_cast<uint64_t>(handles_->NewHandle(klass).GetReference());
         } else {
-          // Class not loaded yet. Fallback to the dex cache.
+          // Class not loaded yet. This happens when the dex code requesting
+          // this `HLoadClass` hasn't been executed in the interpreter.
+          // Fallback to the dex cache.
           // TODO(ngeoffray): Generate HDeoptimize instead.
           desired_load_kind = HLoadClass::LoadKind::kDexCacheViaMethod;
         }