Fix performance regression in DXT5Decoder.js.

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 45b15723dc7ac856ee6c7b19be4c7ea6ec524af9..c345e764564ef9d36851908476dbbb7a75c1d481 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1887,26 +1887,27 @@ LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
   ElementsKind elements_kind = instr->elements_kind();
   bool needs_write_barrier = instr->NeedsWriteBarrier();
   bool clobbers_key = instr->key()->representation().IsTagged();
-  LOperand* key = (clobbers_key || needs_write_barrier)
-      ? UseTempRegister(instr->key())
-      : UseRegisterOrConstantAtStart(instr->key());
-  bool val_is_temp_register =
-      elements_kind == EXTERNAL_PIXEL_ELEMENTS ||
-      elements_kind == EXTERNAL_FLOAT_ELEMENTS;
-  LOperand* val = (needs_write_barrier || val_is_temp_register)
-      ? UseTempRegister(instr->value())
-      : UseRegisterAtStart(instr->value());
   LStoreKeyed* result = NULL;
 
   if (!instr->is_external()) {
     ASSERT(instr->elements()->representation().IsTagged());
 
     LOperand* object = NULL;
+    LOperand* key = NULL;
+    LOperand* val = NULL;
     if (instr->value()->representation().IsDouble()) {
       object = UseRegisterAtStart(instr->elements());
+      val = UseTempRegister(instr->value());
+      key = clobbers_key ? UseTempRegister(instr->key())
+          : UseRegisterOrConstantAtStart(instr->key());
     } else {
       ASSERT(instr->value()->representation().IsTagged());
       object = UseTempRegister(instr->elements());
+      val = needs_write_barrier ? UseTempRegister(instr->value())
+          : UseRegisterAtStart(instr->value());
+      key = (clobbers_key || needs_write_barrier)
+          ? UseTempRegister(instr->key())
+          : UseRegisterOrConstantAtStart(instr->key());
     }
 
     result = new(zone()) LStoreKeyed(object, key, val);
@@ -1919,7 +1920,13 @@ LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
          ((elements_kind == EXTERNAL_FLOAT_ELEMENTS) ||
           (elements_kind == EXTERNAL_DOUBLE_ELEMENTS))));
     ASSERT(instr->elements()->representation().IsExternal());
-
+    bool val_is_temp_register =
+        elements_kind == EXTERNAL_PIXEL_ELEMENTS ||
+        elements_kind == EXTERNAL_FLOAT_ELEMENTS;
+    LOperand* val = val_is_temp_register ? UseTempRegister(instr->value())
+        : UseRegister(instr->value());
+    LOperand* key = clobbers_key ? UseTempRegister(instr->key())
+        : UseRegisterOrConstantAtStart(instr->key());
     LOperand* external_pointer = UseRegister(instr->elements());
     result = new(zone()) LStoreKeyed(external_pointer, key, val);
   }