Ensure that BoxInt32 input is correctly preserved on the slow-path.

runtime/vm/intermediate_language_arm.cc

Index: runtime/vm/intermediate_language_arm.cc
diff --git a/runtime/vm/intermediate_language_arm.cc b/runtime/vm/intermediate_language_arm.cc
index 28b7aaa4875bd8ba421c8f40920faa7cfd9d82a6..b813d1df92218581e424bfeabacb04f7011fe9dc 100644
--- a/runtime/vm/intermediate_language_arm.cc
+++ b/runtime/vm/intermediate_language_arm.cc
@@ -2014,6 +2014,12 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
     const Register temp2 = locs()->temp(1).reg();
     const DRegister fpu_temp = EvenDRegisterOf(locs()->temp(2).fpu_reg());
 
+    if (ShouldEmitStoreBarrier()) {
+      // Value input is a writable register and should be manually preserved
+      // across allocation slow-path.
+      locs()->live_registers()->Add(locs()->in(1), kTagged);
+    }
+
     Label store_pointer;
     Label store_double;
     Label store_float32x4;