ART: Introduce Uint8 loads in compiled code.

Some vectorization patterns are not recognized anymore.
This shall be fixed later.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: testrunner.py --target --optimizing on Nexus 5X
Test: Nexus 5X boots.
Bug: 23964345
Bug: 67935418
Change-Id: I587a328d4799529949c86fa8045c6df21e3a8617
diff --git a/compiler/optimizing/nodes_shared.cc b/compiler/optimizing/nodes_shared.cc
index f982523..2f971b9 100644
--- a/compiler/optimizing/nodes_shared.cc
+++ b/compiler/optimizing/nodes_shared.cc
@@ -54,6 +54,9 @@
       // default encoding 'LSL 0'.
       *op_kind = kLSL;
       *shift_amount = 0;
+    } else if (result_type == DataType::Type::kUint8 ||
+               (input_type == DataType::Type::kUint8 && input_size < result_size)) {
+      *op_kind = kUXTB;
     } else if (result_type == DataType::Type::kUint16 ||
                (input_type == DataType::Type::kUint16 && input_size < result_size)) {
       *op_kind = kUXTH;