Cache current thread in a reserved register and use it in LoadIsolate

runtime/vm/assembler_arm_test.cc

Index: runtime/vm/assembler_arm_test.cc
diff --git a/runtime/vm/assembler_arm_test.cc b/runtime/vm/assembler_arm_test.cc
index a5292148754808fe88455f09e5d100fb085b5795..2cc40fdeb9a0c1b4ad65cbd1986ef3b12823473c 100644
--- a/runtime/vm/assembler_arm_test.cc
+++ b/runtime/vm/assembler_arm_test.cc
@@ -3931,13 +3931,15 @@ ASSEMBLER_TEST_RUN(Vnegqs, test) {
 // R0: context.
 // R1: value.
 // R2: growable array.
+// R3: current thread.
 ASSEMBLER_TEST_GENERATE(StoreIntoObject, assembler) {
-  __ PushList((1 << CTX) | (1 << LR));
+  __ PushList((1 << CTX) | (1 << LR) | (1 << THR));
   __ mov(CTX, Operand(R0));
+  __ mov(THR, Operand(R3));
   __ StoreIntoObject(R2,
                      FieldAddress(R2, GrowableObjectArray::data_offset()),
                      R1);
-  __ PopList((1 << CTX) | (1 << LR));
+  __ PopList((1 << CTX) | (1 << LR) | (1 << THR));
   __ Ret();
 }