Some improvements in register usage in lithium compilation of LoadKeyed/StoreKeyed operations.

src/arm/lithium-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
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 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1857 matching lines @@
     }
     result = new(zone()) LLoadKeyed(obj, key);
   } else {
     ASSERT(
         (instr->representation().IsInteger32() &&
          (elements_kind != EXTERNAL_FLOAT_ELEMENTS) &&
          (elements_kind != EXTERNAL_DOUBLE_ELEMENTS)) ||
         (instr->representation().IsDouble() &&
          ((elements_kind == EXTERNAL_FLOAT_ELEMENTS) ||
           (elements_kind == EXTERNAL_DOUBLE_ELEMENTS))));
-    LOperand* external_pointer = UseRegister(instr->elements());
+
+    LOperand* external_pointer;
+    // We only need a long-lived register for constant keys with an offset
+    if (instr->key()->IsConstant() && instr->index_offset() != 0) {
+      external_pointer = UseRegister(instr->elements());
+    } else {
+      external_pointer = UseRegisterAtStart(instr->elements());

[danno, 2012/11/07 22:34:38]

I don't see the difference in these two case in the codegen file, and in
practice since there are no temp registers, it probably doesn't make a
difference (I am not 100% sure whether UseRegister overlaps with the return
register. If it really doesn't make a difference, UseRegister all the time
probably will simplify the code.

[mvstanton, 2012/11/09 09:43:13]

Done.

+    }
+
     result = new(zone()) LLoadKeyed(external_pointer, key);
   }
 
   DefineAsRegister(result);
   // An unsigned int array load might overflow and cause a deopt, make sure it
   // has an environment.
   bool can_deoptimize = instr->RequiresHoleCheck() ||
       (elements_kind == EXTERNAL_UNSIGNED_INT_ELEMENTS);
   return can_deoptimize ? AssignEnvironment(result) : result;
 }
 
 
 LInstruction* LChunkBuilder::DoLoadKeyedGeneric(HLoadKeyedGeneric* instr) {
   LOperand* object = UseFixed(instr->object(), r1);
   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());
+  LOperand* elements = UseRegisterAtStart(instr->elements());
+  LOperand* key;
+  LOperand* val;
+  if (instr->NeedsWriteBarrier()) {
+    key = UseTempRegister(instr->key());
+    val = UseTempRegister(instr->value());
+  } else {
+    key = UseRegisterOrConstantAtStart(instr->key());
+    val = UseRegisterAtStart(instr->value());
+  }
 
-  LStoreKeyed* result = NULL;
+#ifdef DEBUG
   if (!instr->is_external()) {
     ASSERT(instr->elements()->representation().IsTagged());
-
-    LOperand* object = NULL;
-    if (instr->value()->representation().IsDouble()) {
-      object = UseRegisterAtStart(instr->elements());
-    } else {
-      ASSERT(instr->value()->representation().IsTagged());
-      object = UseTempRegister(instr->elements());
-    }
-
-    result = new(zone()) LStoreKeyed(object, key, val);
   } else {
+    ElementsKind elements_kind = instr->elements_kind();
     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());
+  }
+#endif
 
-    LOperand* external_pointer = UseRegister(instr->elements());
-    result = new(zone()) LStoreKeyed(external_pointer, key, val);
-  }
-
+  LStoreKeyed* result = new(zone()) LStoreKeyed(elements, key, val);
   ASSERT(result != NULL);
   return result;
 }
 
 
 LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
   LOperand* obj = UseFixed(instr->object(), r2);
   LOperand* key = UseFixed(instr->key(), r1);
   LOperand* val = UseFixed(instr->value(), r0);
 
@@ skipping 315 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