MIPS: Elide unnecessary context reload in generated stubs.

Port r13290 (6970ca83)

BUG=
TEST=

Review URL: https://codereview.chromium.org/11773013
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13323 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -2468,9 +2468,6 @@ void LCodeGen::DoReturn(LReturn* instr) {
     __ Pop(ra, fp);
     __ Addu(sp, sp, Operand(sp_delta));
   }
-  if (info()->IsStub()) {
-    __ lw(cp, MemOperand(fp, StandardFrameConstants::kContextOffset));
-  }
   __ Jump(ra);
 }
 

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;
 }