Clobber non-live temporaries on some paths involving a possible slow-path allocation.

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 745134c571ebc5ff405f391a4d4dc0c33363cc0f..452b2fe10b318abff58640b92001d977b8ece8e3 100644
--- a/runtime/vm/intermediate_language_arm.cc
+++ b/runtime/vm/intermediate_language_arm.cc
@@ -1962,6 +1962,9 @@ void LoadCodeUnitsInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       // If the value cannot fit in a smi then allocate a mint box for it.
       Register value = locs()->temp(0).reg();
       Register temp = locs()->temp(1).reg();
+      // Value register needs to be manually preserved on allocation slow-path.
+      locs()->live_registers()->Add(locs()->temp(0), kUnboxedInt32);
+
       ASSERT(result != value);
       __ MoveRegister(value, result);
       __ SmiTag(result);