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

runtime/vm/flow_graph_compiler_mips.cc

Index: runtime/vm/flow_graph_compiler_mips.cc
diff --git a/runtime/vm/flow_graph_compiler_mips.cc b/runtime/vm/flow_graph_compiler_mips.cc
index 34349845183428319eb334a29050b93f4c0be18f..c273ee80931b5288af03dffda5d42246fa079df2 100644
--- a/runtime/vm/flow_graph_compiler_mips.cc
+++ b/runtime/vm/flow_graph_compiler_mips.cc
@@ -1470,6 +1470,7 @@ void FlowGraphCompiler::EmitEqualityRegRegCompare(Register left,
 void FlowGraphCompiler::SaveLiveRegisters(LocationSummary* locs) {
 #if defined(DEBUG)
   locs->CheckWritableInputs();
+  ClobberDeadTempRegisters(locs);
 #endif
 
   __ TraceSimMsg("SaveLiveRegisters");
@@ -1512,6 +1513,9 @@ 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.
   __ TraceSimMsg("RestoreLiveRegisters");
@@ -1548,6 +1552,21 @@ 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())) {
+      __ LoadImmediate(tmp.reg(), 0xf7);
+    }
+  }
+}
+#endif
+
+
 void FlowGraphCompiler::EmitTestAndCall(const ICData& ic_data,
                                         Register class_id_reg,
                                         intptr_t argument_count,