Fix performance regression in DXT5Decoder.js.

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 fa84882718f43bee4472ac6c977c4e8054378d01..60c289de4efe04e79c5c5d24e0d953f1f1e2487e 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -1844,26 +1844,26 @@ LInstruction* LChunkBuilder::DoLoadKeyedGeneric(HLoadKeyedGeneric* instr) {
 
 LInstruction* LChunkBuilder::DoStoreKeyed(HStoreKeyed* instr) {
   ElementsKind elements_kind = instr->elements_kind();
-  bool needs_write_barrier = instr->NeedsWriteBarrier();
-  LOperand* 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 = val_is_temp_register || needs_write_barrier
-      ? UseTempRegister(instr->value())
-      : UseRegister(instr->value());
   LStoreKeyed* result = NULL;
+
   if (!instr->is_external()) {
     ASSERT(instr->elements()->representation().IsTagged());
-
+    bool needs_write_barrier = instr->NeedsWriteBarrier();
     LOperand* object = NULL;
+    LOperand* val = NULL;
+    LOperand* key = NULL;
+
     if (instr->value()->representation().IsDouble()) {
       object = UseRegisterAtStart(instr->elements());
+      key = UseRegisterOrConstantAtStart(instr->key());
+      val = UseTempRegister(instr->value());
     } else {
       ASSERT(instr->value()->representation().IsTagged());
       object = UseTempRegister(instr->elements());
+      val = needs_write_barrier ? UseTempRegister(instr->value())
+          : UseRegisterAtStart(instr->value());
+      key = needs_write_barrier ? UseTempRegister(instr->key())
+          : UseRegisterOrConstantAtStart(instr->key());
     }
 
     result = new(zone()) LStoreKeyed(object, key, val);
@@ -1876,8 +1876,14 @@ 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 = UseRegisterOrConstantAtStart(instr->key());
     LOperand* external_pointer = UseRegister(instr->elements());
+
     result = new(zone()) LStoreKeyed(external_pointer, key, val);
   }