Don't emit code for HContext values with no uses.

BUG=
TEST=

Review URL: http://codereview.chromium.org/6982023

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7860 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-arm.cc

@@ -1202,7 +1202,7 @@ LInstruction* LChunkBuilder::DoPushArgument(HPushArgument* instr) {
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
-  return DefineAsRegister(new LContext);
+  return instr->HasNoUses() ? NULL : DefineAsRegister(new LContext);
 }
 
 

src/ia32/lithium-ia32.cc

@@ -1214,7 +1214,7 @@ LInstruction* LChunkBuilder::DoPushArgument(HPushArgument* instr) {
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
-  return DefineAsRegister(new LContext);
+  return instr->HasNoUses() ? NULL : DefineAsRegister(new LContext);
 }
 
 

src/x64/lithium-x64.cc

@@ -1202,7 +1202,7 @@ LInstruction* LChunkBuilder::DoPushArgument(HPushArgument* instr) {
 
 
 LInstruction* LChunkBuilder::DoContext(HContext* instr) {
-  return DefineAsRegister(new LContext);
+  return instr->HasNoUses() ? NULL : DefineAsRegister(new LContext);
 }