[Turbofan] Simplified lowering to be done concurrently.

R=jarin@chromium.org
BUG=v8:5428

Review-Url: https://codereview.chromium.org/2611523002
Cr-Commit-Position: refs/heads/master@{#42012}

src/compiler/pipeline.cc

@@ -945,8 +945,8 @@ struct EscapeAnalysisPhase {
   }
 };
 
-struct RepresentationSelectionPhase {
-  static const char* phase_name() { return "representation selection"; }
+struct SimplifiedLoweringPhase {
+  static const char* phase_name() { return "simplified lowering"; }
 
   void Run(PipelineData* data, Zone* temp_zone) {
     SimplifiedLowering lowering(data->jsgraph(), temp_zone,
@@ -1553,11 +1553,22 @@ bool PipelineImpl::CreateGraph() {
     }
   }
 
-  // Select representations. This has to run w/o the Typer decorator, because
-  // we cannot compute meaningful types anyways, and the computed types might
-  // even conflict with the representation/truncation logic.
-  Run<RepresentationSelectionPhase>();
-  RunPrintAndVerify("Representations selected", true);
+  // Do some hacky things to prepare generic lowering.
+  Run<GenericLoweringPrepPhase>();
+
+  data->EndPhaseKind();
+
+  return true;
+}
+
+bool PipelineImpl::OptimizeGraph(Linkage* linkage) {
+  PipelineData* data = this->data_;
+
+  // Perform simplified lowering. This has to run w/o the Typer decorator,
+  // because we cannot compute meaningful types anyways, and the computed types
+  // might even conflict with the representation/truncation logic.
+  Run<SimplifiedLoweringPhase>();
+  RunPrintAndVerify("Simplified lowering", true);
 
 #ifdef DEBUG
   // From now on it is invalid to look at types on the nodes, because:
@@ -1576,17 +1587,6 @@ bool PipelineImpl::CreateGraph() {
   RunPrintAndVerify("Untyped", true);
 #endif
 
-  // Do some hacky things to prepare generic lowering.
-  Run<GenericLoweringPrepPhase>();
-
-  data->EndPhaseKind();
-
-  return true;
-}
-
-bool PipelineImpl::OptimizeGraph(Linkage* linkage) {
-  PipelineData* data = this->data_;
-
   // Run generic lowering pass.
   Run<GenericLoweringPhase>();
   RunPrintAndVerify("Generic lowering", true);

src/compiler/representation-change.cc

@@ -9,6 +9,7 @@
 #include "src/base/bits.h"
 #include "src/code-factory.h"
 #include "src/compiler/machine-operator.h"
+#include "src/compiler/node-matchers.h"
 
 namespace v8 {
 namespace internal {
@@ -694,8 +695,12 @@ Node* RepresentationChanger::GetBitRepresentationFor(
   // Eagerly fold representation changes for constants.
   switch (node->opcode()) {
     case IrOpcode::kHeapConstant: {
-      Handle<HeapObject> value = OpParameter<Handle<HeapObject>>(node);
-      return jsgraph()->Int32Constant(value->BooleanValue() ? 1 : 0);
+      HeapObjectMatcher m(node);
+      if (m.Is(factory()->false_value())) {
+        return jsgraph()->Int32Constant(0);
+      } else if (m.Is(factory()->true_value())) {
+        return jsgraph()->Int32Constant(1);
+      }
     }
     default:
       break;

src/compiler/simplified-lowering.cc

@@ -1109,17 +1109,14 @@ class RepresentationSelector {
         return kNoWriteBarrier;
       }
       if (value_type->IsHeapConstant()) {
-        Handle<HeapObject> value_object = value_type->AsHeapConstant()->Value();
-        RootIndexMap root_index_map(jsgraph_->isolate());
-        int root_index = root_index_map.Lookup(*value_object);
-        if (root_index != RootIndexMap::kInvalidRootIndex &&
-            jsgraph_->isolate()->heap()->RootIsImmortalImmovable(root_index)) {
-          // Write barriers are unnecessary for immortal immovable roots.
-          return kNoWriteBarrier;
-        }
-        if (value_object->IsMap()) {
-          // Write barriers for storing maps are cheaper.
-          return kMapWriteBarrier;
+        Heap::RootListIndex root_index;
+        Heap* heap = jsgraph_->isolate()->heap();
+        if (heap->IsRootHandle(value_type->AsHeapConstant()->Value(),
+                               &root_index)) {
+          if (heap->RootIsImmortalImmovable(root_index)) {
+            // Write barriers are unnecessary for immortal immovable roots.
+            return kNoWriteBarrier;
+          }
         }
       }
       if (field_representation == MachineRepresentation::kTaggedPointer ||