Improvements in lithium code generation. Recognizing if some operands are constants, we can often s…

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index ba29ed969df4e811c9f409ab955b499f8a9ce970..824e3b1a526413c0524c4bfa45519b4835e32ada 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2133,7 +2133,7 @@ LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
       ASSERT(instr->value()->representation().IsTagged());
       object = UseTempRegister(instr->elements());
       val = needs_write_barrier ? UseTempRegister(instr->value())
-          : UseRegisterAtStart(instr->value());
+          : UseRegisterOrConstantAtStart(instr->value());
       key = (clobbers_key || needs_write_barrier)
           ? UseTempRegister(instr->key())
           : UseRegisterOrConstantAtStart(instr->key());
@@ -2230,9 +2230,22 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
         : UseRegisterAtStart(instr->object());
   }
 
-  LOperand* val = needs_write_barrier
-      ? UseTempRegister(instr->value())
-      : UseRegister(instr->value());
+  LOperand* val = NULL;
+  if (needs_write_barrier) {
+    val = UseTempRegister(instr->value());
+  } else if (instr->value()->IsConstant()) {
+    // If it's tagged, it might still be in new space
+    HConstant* constant_value = HConstant::cast(instr->value());
+    if (constant_value->HasInteger32Value() ||
+        constant_value->HasDoubleValue() ||
+        constant_value->ImmortalImmovable()) {
+      val = UseRegisterOrConstant(instr->value());
+    }
+  }
+
+  if (val == NULL) {
+    val = UseRegister(instr->value());
+  }
 
   // We only need a scratch register if we have a write barrier or we
   // have a store into the properties array (not in-object-property).
@@ -2375,8 +2388,15 @@ LInstruction* LChunkBuilder::DoArgumentsObject(HArgumentsObject* instr) {
 
 LInstruction* LChunkBuilder::DoAccessArgumentsAt(HAccessArgumentsAt* instr) {
   LOperand* args = UseRegister(instr->arguments());
-  LOperand* length = UseTempRegister(instr->length());
-  LOperand* index = Use(instr->index());
+  LOperand* length;
+  LOperand* index;
+  if (instr->length()->IsConstant() && instr->index()->IsConstant()) {
+    length = UseRegisterOrConstant(instr->length());
+    index = UseOrConstant(instr->index());
+  } else {
+    length = UseTempRegister(instr->length());
+    index = Use(instr->index());
+  }
   return DefineAsRegister(new(zone()) LAccessArgumentsAt(args, length, index));
 }