MIPS: Elide unnecessary context reload in generated stubs.

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index b883ad459eb1879a6ccce5724d2d87784d91337c..3d5d663e6716e391d71ac8130e27a493b872474e 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -1002,7 +1002,14 @@ LInstruction* LChunkBuilder::DoThisFunction(HThisFunction* instr) {
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
-  return instr->HasNoUses() ? NULL : DefineAsRegister(new(zone()) LContext);
+  // If there is a non-return use, the context must be allocated in a register.
+  for (HUseIterator it(instr->uses()); !it.Done(); it.Advance()) {
+    if (!it.value()->IsReturn()) {
+      return DefineAsRegister(new(zone()) LContext);
+    }
+  }
+
+  return NULL;
 }