[turbofan] Relax effects and context for JSToNumber(x:plain-primitive).

src/compiler/js-typed-lowering.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/access-builder.h"
 #include "src/compiler/graph-inl.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-typed-lowering.h"
 #include "src/compiler/node-aux-data-inl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties-inl.h"
 #include "src/types.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // TODO(turbofan): js-typed-lowering improvements possible
 // - immediately put in type bounds for all new nodes
 // - relax effects from generic but not-side-effecting operations
-// - relax effects for ToNumber(mixed)
 
 
 // Relax the effects of {node} by immediately replacing effect uses of {node}
 // with the effect input to {node}.
 // TODO(turbofan): replace the effect input to {node} with {graph->start()}.
 // TODO(titzer): move into a GraphEditor?
 static void RelaxEffects(Node* node) {
   NodeProperties::ReplaceWithValue(node, node, NULL);
 }
 
@@ skipping 619 matching lines @@
 Reduction JSTypedLowering::ReduceJSToNumber(Node* node) {
   // Try to reduce the input first.
   Node* const input = node->InputAt(0);
   Reduction reduction = ReduceJSToNumberInput(input);
   if (reduction.Changed()) {
     NodeProperties::ReplaceWithValue(node, reduction.replacement());
     return reduction;
   }
   Type* const input_type = NodeProperties::GetBounds(input).upper;
   if (input_type->Is(Type::PlainPrimitive())) {
-    // Converting a plain primitive to a number has no observable side effects.
-    RelaxEffects(node);
     if (input->opcode() == IrOpcode::kPhi) {
       // JSToNumber(phi(x1,...,xn,control):plain-primitive,context)
       //   => phi(JSToNumber(x1,no-context),
       //          ...,
       //          JSToNumber(xn,no-context),control)
       int const input_count = input->InputCount() - 1;
       Node* const control = input->InputAt(input_count);
       DCHECK_LE(0, input_count);
       DCHECK(NodeProperties::IsControl(control));
       DCHECK(NodeProperties::GetBounds(node).upper->Is(Type::Number()));
       DCHECK(!NodeProperties::GetBounds(input).upper->Is(Type::Number()));
+      RelaxEffects(node);
       node->set_op(common()->Phi(kMachAnyTagged, input_count));
       for (int i = 0; i < input_count; ++i) {
         Node* value = input->InputAt(i);
         // Recursively try to reduce the value first.
         Reduction reduction = ReduceJSToNumberInput(value);
         if (reduction.Changed()) {
           value = reduction.replacement();
         } else {
           // We must be very careful not to introduce cycles when pushing
           // operations into phis. It is safe for {value}, since it appears
@@ skipping 10 matching lines @@
         } else {
           node->AppendInput(graph()->zone(), value);
         }
       }
       if (input_count < node->InputCount()) {
         node->ReplaceInput(input_count, control);
       } else {
         node->AppendInput(graph()->zone(), control);
       }
       node->TrimInputCount(input_count + 1);
-    } else if (input->opcode() == IrOpcode::kSelect) {
+      return Changed(node);
+    }
+    if (input->opcode() == IrOpcode::kSelect) {
       // JSToNumber(select(c,x1,x2):plain-primitive,context)
       //   => select(c,JSToNumber(x1,no-context),JSToNumber(x2,no-context))
       int const input_count = input->InputCount();
       BranchHint const input_hint = SelectParametersOf(input->op()).hint();
       DCHECK_EQ(3, input_count);
       DCHECK(NodeProperties::GetBounds(node).upper->Is(Type::Number()));
       DCHECK(!NodeProperties::GetBounds(input).upper->Is(Type::Number()));
+      RelaxEffects(node);
       node->set_op(common()->Select(kMachAnyTagged, input_hint));
       node->ReplaceInput(0, input->InputAt(0));
       for (int i = 1; i < input_count; ++i) {
         Node* value = input->InputAt(i);
         // Recursively try to reduce the value first.
         Reduction reduction = ReduceJSToNumberInput(value);
         if (reduction.Changed()) {
           value = reduction.replacement();
         } else {
           // We must be very careful not to introduce cycles when pushing
           // operations into selects. It is safe for {value}, since it appears
           // as input to the select that we are replacing, but it's not safe
           // to simply reuse the context of the {node}. However, ToNumber()
           // does not require a context anyways, so it's safe to discard it
           // here and pass the dummy context.
           value = graph()->NewNode(javascript()->ToNumber(), value,
                                    jsgraph()->NoContextConstant(),
                                    graph()->start(), graph()->start());
         }
         node->ReplaceInput(i, value);
       }
       node->TrimInputCount(input_count);
+      return Changed(node);
     }
-    return Changed(node);
+    if (node->InputAt(1) != jsgraph()->NoContextConstant() ||
+        node->InputAt(2) != graph()->start()) {
+      // JSToNumber(x:plain-primitive,context) => JSToNumber(x,no-context)
+      node->ReplaceInput(1, jsgraph()->NoContextConstant());
+      RelaxEffects(node);
+      return Changed(node);
+    }
   }
   return NoChange();
 }
 
 
 Reduction JSTypedLowering::ReduceJSToStringInput(Node* input) {
   if (input->opcode() == IrOpcode::kJSToString) {
     // Recursively try to reduce the input first.
     Reduction result = ReduceJSToString(input);
     if (result.Changed()) return result;
@@ skipping 291 matching lines @@
 }
 
 
 MachineOperatorBuilder* JSTypedLowering::machine() const {
   return jsgraph()->machine();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8