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

runtime/vm/flow_graph_compiler_arm.cc

Index: runtime/vm/flow_graph_compiler_arm.cc
diff --git a/runtime/vm/flow_graph_compiler_arm.cc b/runtime/vm/flow_graph_compiler_arm.cc
index 9f2941ae4a022a4a1c5aa8aaee631e66fb33c5f1..b036d22537d58929028cd59c02aa607e9ffae7e2 100644
--- a/runtime/vm/flow_graph_compiler_arm.cc
+++ b/runtime/vm/flow_graph_compiler_arm.cc
@@ -1425,6 +1425,7 @@ void FlowGraphCompiler::EmitEqualityRegRegCompare(Register left,
 void FlowGraphCompiler::SaveLiveRegisters(LocationSummary* locs) {
 #if defined(DEBUG)
   locs->CheckWritableInputs();
+  ClobberDeadTempRegisters(locs);
 #endif
 
   // TODO(vegorov): consider saving only caller save (volatile) registers.
@@ -1463,6 +1464,10 @@ void FlowGraphCompiler::SaveLiveRegisters(LocationSummary* locs) {
 
 
 void FlowGraphCompiler::RestoreLiveRegisters(LocationSummary* locs) {
+#if defined(DEBUG)
+  ClobberDeadTempRegisters(locs);
+#endif
+
   // General purpose registers have the highest register number at the
   // lowest address.
   for (intptr_t reg_idx = kNumberOfCpuRegisters - 1; reg_idx >= 0; --reg_idx) {
@@ -1493,6 +1498,21 @@ void FlowGraphCompiler::RestoreLiveRegisters(LocationSummary* locs) {
 }
 
 
+#if defined(DEBUG)
+void FlowGraphCompiler::ClobberDeadTempRegisters(LocationSummary* locs) {
+  // Clobber temporaries that have not been manually preserved.
+  for (intptr_t i = 0; i < locs->temp_count(); ++i) {
+    Location tmp = locs->temp(i);
+    // TODO(zerny): clobber non-live temporary FPU registers.
+    if (tmp.IsRegister() &&
+        !locs->live_registers()->ContainsRegister(tmp.reg())) {
+      __ mov(tmp.reg(), Operand(0xf7));
+    }
+  }
+}
+#endif
+
+
 void FlowGraphCompiler::EmitTestAndCall(const ICData& ic_data,
                                         Register class_id_reg,
                                         intptr_t argument_count,