Fix performance regression in DXT5Decoder.js.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 5cd691461f6308949bb47ef62e66fc5f4edcd355..91077cd259b011cb2e820410325085cf4307235f 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1934,27 +1934,26 @@ 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* key = NULL;
+    LOperand* val = 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.

@@ -1967,7 +1966,12 @@ 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);
   }