ARM: Don't emit a write barrier for an inlined keyed load...

src/arm/codegen-arm.cc

Index: src/arm/codegen-arm.cc
===================================================================
--- src/arm/codegen-arm.cc	(revision 4996)
+++ src/arm/codegen-arm.cc	(working copy)
@@ -1745,11 +1745,15 @@
     val = node->fun();  // NULL if we don't have a function
   }
 
+
   if (val != NULL) {
+    WriteBarrierCharacter wb_info =
+        val->type()->IsLikelySmi() ? LIKELY_SMI : UNLIKELY_SMI;
+    if (val->AsLiteral() != NULL) wb_info = NEVER_NEWSPACE;
     // Set initial value.
     Reference target(this, node->proxy());
     Load(val);
-    target.SetValue(NOT_CONST_INIT);
+    target.SetValue(NOT_CONST_INIT, wb_info);
 
     // Get rid of the assigned value (declarations are statements).
     frame_->Drop();
@@ -2485,13 +2489,13 @@
       if (each.size() > 0) {
         __ ldr(r0, frame_->ElementAt(each.size()));
         frame_->EmitPush(r0);
-        each.SetValue(NOT_CONST_INIT);
+        each.SetValue(NOT_CONST_INIT, UNLIKELY_SMI);
         frame_->Drop(2);
       } else {
         // If the reference was to a slot we rely on the convenient property
         // that it doesn't matter whether a value (eg, r3 pushed above) is
         // right on top of or right underneath a zero-sized reference.
-        each.SetValue(NOT_CONST_INIT);
+        each.SetValue(NOT_CONST_INIT, UNLIKELY_SMI);
         frame_->Drop();
       }
     }
@@ -3646,6 +3650,8 @@
   // Evaluate the receiver subexpression.
   Load(prop->obj());
 
+  WriteBarrierCharacter wb_info;
+
   // Change to slow case in the beginning of an initialization block to
   // avoid the quadratic behavior of repeatedly adding fast properties.
   if (node->starts_initialization_block()) {
@@ -3667,7 +3673,7 @@
   // [tos]   : key
   // [tos+1] : receiver
   // [tos+2] : receiver if at the end of an initialization block
-
+  //
   // Evaluate the right-hand side.
   if (node->is_compound()) {
     // For a compound assignment the right-hand side is a binary operation
@@ -3699,9 +3705,13 @@
                              overwrite_value ? OVERWRITE_RIGHT : NO_OVERWRITE,
                              inline_smi);
     }
+    wb_info = node->type()->IsLikelySmi() ? LIKELY_SMI : UNLIKELY_SMI;
   } else {
     // For non-compound assignment just load the right-hand side.
     Load(node->value());
+    wb_info = node->value()->AsLiteral() != NULL ?
+        NEVER_NEWSPACE :
+        (node->value()->type()->IsLikelySmi() ? LIKELY_SMI : UNLIKELY_SMI);
   }
 
   // Stack layout:
@@ -3713,7 +3723,7 @@
   // Perform the assignment.  It is safe to ignore constants here.
   ASSERT(node->op() != Token::INIT_CONST);
   CodeForSourcePosition(node->position());
-  EmitKeyedStore(prop->key()->type());
+  EmitKeyedStore(prop->key()->type(), wb_info);
   frame_->EmitPush(r0);
 
   // Stack layout:
@@ -5509,7 +5519,7 @@
       __ sub(value, value, Operand(Smi::FromInt(1)));
     }
     frame_->EmitPush(value);
-    target.SetValue(NOT_CONST_INIT);
+    target.SetValue(NOT_CONST_INIT, LIKELY_SMI);
     if (is_postfix) frame_->Pop();
     ASSERT_EQ(original_height + 1, frame_->height());
     return;
@@ -5608,7 +5618,7 @@
     // Set the target with the result, leaving the result on
     // top of the stack.  Removes the target from the stack if
     // it has a non-zero size.
-    if (!is_const) target.SetValue(NOT_CONST_INIT);
+    if (!is_const) target.SetValue(NOT_CONST_INIT, LIKELY_SMI);
   }
 
   // Postfix: Discard the new value and use the old.
@@ -6341,7 +6351,8 @@
 }
 
 
-void CodeGenerator::EmitKeyedStore(StaticType* key_type) {
+void CodeGenerator::EmitKeyedStore(StaticType* key_type,
+                                   WriteBarrierCharacter wb_info) {
   // Generate inlined version of the keyed store if the code is in a loop
   // and the key is likely to be a smi.
   if (loop_nesting() > 0 && key_type->IsLikelySmi()) {
@@ -6357,25 +6368,45 @@
     __ IncrementCounter(&Counters::keyed_store_inline, 1,
                         scratch1, scratch2);
 
+
+
     // Load the value, key and receiver from the stack.
+    bool value_is_harmless = frame_->KnownSmiAt(0);
+    if (wb_info == NEVER_NEWSPACE) value_is_harmless = true;
+    bool key_is_smi = frame_->KnownSmiAt(1);
     Register value = frame_->PopToRegister();
     Register key = frame_->PopToRegister(value);
     VirtualFrame::SpilledScope spilled(frame_);
     Register receiver = r2;
     frame_->EmitPop(receiver);
 
+#ifdef DEBUG
+    bool we_remembered_the_write_barrier = value_is_harmless;
+#endif
+
     // The deferred code expects value, key and receiver in registers.
     DeferredReferenceSetKeyedValue* deferred =
         new DeferredReferenceSetKeyedValue(value, key, receiver);
 
     // Check that the value is a smi. As this inlined code does not set the
     // write barrier it is only possible to store smi values.
-    __ tst(value, Operand(kSmiTagMask));
-    deferred->Branch(ne);
+    if (!value_is_harmless) {
+      // If the value is not likely to be a Smi then lets test the fixed array

[William Hesse, 2010/07/01 15:00:59]

let's

+      // for new space instead.  See below.
+      if (wb_info == LIKELY_SMI) {
+        __ tst(value, Operand(kSmiTagMask));
+        deferred->Branch(ne);
+#ifdef DEBUG
+        we_remembered_the_write_barrier = true;
+#endif
+      }
+    }
 
-    // Check that the key is a smi.
-    __ tst(key, Operand(kSmiTagMask));
-    deferred->Branch(ne);
+    if (!key_is_smi) {
+      // Check that the key is a smi.
+      __ tst(key, Operand(kSmiTagMask));
+      deferred->Branch(ne);
+    }
 
     // Check that the receiver is a heap object.
     __ tst(receiver, Operand(kSmiTagMask));
@@ -6391,24 +6422,35 @@
     __ cmp(scratch1, key);
     deferred->Branch(ls);  // Unsigned less equal.
 
+    // Get the elements array from the receiver and check that it
+    // is not a dictionary.

[William Hesse, 2010/07/01 15:00:59]

The check that it is a dictionary is pretty far away from here.

+    __ ldr(scratch1, FieldMemOperand(receiver, JSObject::kElementsOffset));
+    if (!value_is_harmless && wb_info != LIKELY_SMI) {
+      Label ok;
+      __ and_(scratch2, scratch1, Operand(ExternalReference::new_space_mask()));
+      __ cmp(scratch2, Operand(ExternalReference::new_space_start()));
+      __ tst(value, Operand(kSmiTagMask), ne);
+      deferred->Branch(ne);
+#ifdef DEBUG
+      we_remembered_the_write_barrier = true;
+#endif
+    }
+    __ ldr(scratch2, FieldMemOperand(scratch1, JSObject::kMapOffset));
     // The following instructions are the part of the inlined store keyed
     // property code which can be patched. Therefore the exact number of
     // instructions generated need to be fixed, so the constant pool is blocked
     // while generating this code.
     { Assembler::BlockConstPoolScope block_const_pool(masm_);
-      // Get the elements array from the receiver and check that it
-      // is not a dictionary.
-      __ ldr(scratch1, FieldMemOperand(receiver, JSObject::kElementsOffset));
-      __ ldr(scratch2, FieldMemOperand(scratch1, JSObject::kMapOffset));
+#ifdef DEBUG
+      Label check_inlined_codesize;
+      masm_->bind(&check_inlined_codesize);
+#endif
+
       // Read the fixed array map from the constant pool (not from the root
       // array) so that the value can be patched.  When debugging, we patch this
       // comparison to always fail so that we will hit the IC call in the
       // deferred code which will allow the debugger to break for fast case
       // stores.
-#ifdef DEBUG
-    Label check_inlined_codesize;
-    masm_->bind(&check_inlined_codesize);
-#endif
       __ mov(scratch3, Operand(Factory::fixed_array_map()));
       __ cmp(scratch2, scratch3);
       deferred->Branch(ne);
@@ -6425,6 +6467,8 @@
                 masm_->InstructionsGeneratedSince(&check_inlined_codesize));
     }
 
+    ASSERT(we_remembered_the_write_barrier);
+
     deferred->BindExit();
   } else {
     frame()->CallKeyedStoreIC();
@@ -6522,7 +6566,7 @@
 }
 
 
-void Reference::SetValue(InitState init_state) {
+void Reference::SetValue(InitState init_state, WriteBarrierCharacter wb_info) {
   ASSERT(!is_illegal());
   ASSERT(!cgen_->has_cc());
   MacroAssembler* masm = cgen_->masm();
@@ -6554,7 +6598,7 @@
       Property* property = expression_->AsProperty();
       ASSERT(property != NULL);
       cgen_->CodeForSourcePosition(property->position());
-      cgen_->EmitKeyedStore(property->key()->type());
+      cgen_->EmitKeyedStore(property->key()->type(), wb_info);
       frame->EmitPush(r0);
       set_unloaded();
       break;