A64: Improve constraints for StoreNamedField

src/a64/lithium-a64.cc

Index: src/a64/lithium-a64.cc
diff --git a/src/a64/lithium-a64.cc b/src/a64/lithium-a64.cc
index cf89c09f5b2515d2dbc0b6cabe667b10245eb9ea..ce77209910d33131d5ea6607a585d9ccd6f05df2 100644
--- a/src/a64/lithium-a64.cc
+++ b/src/a64/lithium-a64.cc
@@ -2231,17 +2231,27 @@ LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
 
 
 LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
-  // TODO(jbramley): Optimize register usage in this instruction. For now, it
-  // allocates everything that it might need because it keeps changing in the
-  // merge and keeping it valid is time-consuming.
-
   // TODO(jbramley): It might be beneficial to allow value to be a constant in
   // some cases. x64 makes use of this with FLAG_track_fields, for example.
 
   LOperand* object = UseRegister(instr->object());

[ulan, 2014/03/07 15:16:26]

This is difficult to understand and to keep in sync with codegen. I hope it pays
off with performance improvement.

To make reading a little bit easier, could you please rearrange the conditions
to mirror the structure of codegen?

Along these lines:

if (instr->access().IsExternalMemory() ||
instr->field_representation().IsDouble()) {
 ...
} else if (instr->NeedsWriteBarrierForMap() || instr->NeedsWriteBarrier()) {
 ...
} else {
 ...
}

-  LOperand* value = UseRegisterAndClobber(instr->value());
-  LOperand* temp0 = TempRegister();
-  LOperand* temp1 = TempRegister();
+  LOperand* value;
+  LOperand* temp0 = NULL;
+  LOperand* temp1 = NULL;
+  if (instr->NeedsWriteBarrier()) {
+    value = UseRegisterAndClobber(instr->value());
+    temp0 = TempRegister();
+    temp1 = TempRegister();
+  } else {
+    value = UseRegister(instr->value());
+    if (!(instr->access().IsExternalMemory() ||
+          instr->field_representation().IsDouble())) {
+      temp0 = TempRegister();
+      if (instr->NeedsWriteBarrierForMap()) {
+        temp1 = TempRegister();
+      }
+    }
+  }
 
   LStoreNamedField* result =
       new(zone()) LStoreNamedField(object, value, temp0, temp1);