Fix performance regression in DXT5Decoder.js.

src/arm/lithium-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1916 matching lines @@
   LOperand* key = UseFixed(instr->key(), r0);
 
   LInstruction* result =
       DefineFixed(new(zone()) LLoadKeyedGeneric(object, key), r0);
   return MarkAsCall(result, 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;
 
-  LStoreKeyed* result = NULL;
   if (!instr->is_external()) {
     ASSERT(instr->elements()->representation().IsTagged());
+    bool needs_write_barrier = instr->NeedsWriteBarrier();
+    LOperand* object = NULL;
+    LOperand* key = NULL;
+    LOperand* val = NULL;
 
-    LOperand* object = NULL;
     if (instr->value()->representation().IsDouble()) {
       object = UseRegisterAtStart(instr->elements());
+      val = UseTempRegister(instr->value());
+      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 = needs_write_barrier ? UseTempRegister(instr->key())
+          : UseRegisterOrConstantAtStart(instr->key());
     }
 
     result = new(zone()) LStoreKeyed(object, key, val);

[Sven Panne, 2012/11/21 13:30:51]

Directly returning here and below without any temp variable is shorter and
actually clearer, I think. No confusing declaration, no initialization and no
assertion. :-)

[mvstanton, 2012/11/21 13:59:18]

Thanks, that is true! I've adjusted the ia32 file as well because it is similar.

   } else {
     ASSERT(
         (instr->value()->representation().IsInteger32() &&
          (elements_kind != EXTERNAL_FLOAT_ELEMENTS) &&
          (elements_kind != EXTERNAL_DOUBLE_ELEMENTS)) ||
         (instr->value()->representation().IsDouble() &&
          ((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);
   }
 
   ASSERT(result != NULL);
   return result;
 }
 
 
 LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
@@ skipping 319 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseRegister(instr->index());
   return DefineAsRegister(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal