[turbofan] Allow indexed access to node inputs/input_edges

src/compiler/branch-elimination.cc

 // Copyright 2015 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/branch-elimination.h"
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/simplified-operator.h"
 
@@ skipping 127 matching lines @@
   // Here we rely on having only reducible loops:
   // The loop entry edge always dominates the header, so we can just use
   // the information from the loop entry edge.
   return TakeConditionsFromFirstControl(node);
 }
 
 
 Reduction BranchElimination::ReduceMerge(Node* node) {
   // Shortcut for the case when we do not know anything about some
   // input.
-  for (Node* input : node->inputs()) {
+  Node::Inputs inputs = node->inputs();
+  for (Node* input : inputs) {
     if (node_conditions_.Get(input) == nullptr) {
       return UpdateConditions(node, nullptr);
     }
   }
 
-  const ControlPathConditions* first = node_conditions_.Get(node->InputAt(0));
+  auto input_it = inputs.begin();
+
+  DCHECK_GT(inputs.count(), 0);
+
+  const ControlPathConditions* first = node_conditions_.Get(*input_it);
+  ++input_it;
   // Make a copy of the first input's conditions and merge with the conditions
   // from other inputs.
   ControlPathConditions* conditions =
       new (zone_->New(sizeof(ControlPathConditions)))
           ControlPathConditions(*first);
-  for (int i = 1; i < node->InputCount(); i++) {
-    conditions->Merge(*(node_conditions_.Get(node->InputAt(i))));
+  auto input_end = inputs.end();
+  for (; input_it != input_end; ++input_it) {
+    conditions->Merge(*(node_conditions_.Get(*input_it)));

[Jarin, 2017/01/10 10:53:38]

Again, this is longer and harder to read.

[Leszek Swirski, 2017/01/10 12:03:38]

This one I'd rather keep, merges can have a lot of inputs, and the new version
is 531 bytes vs. 656 (on x64 release).

   }
 
   return UpdateConditions(node, conditions);
 }
 
 
 Reduction BranchElimination::ReduceStart(Node* node) {
   return UpdateConditions(node, ControlPathConditions::Empty(zone_));
 }
 
@@ skipping 134 matching lines @@
 
 Graph* BranchElimination::graph() const { return jsgraph()->graph(); }
 
 CommonOperatorBuilder* BranchElimination::common() const {
   return jsgraph()->common();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8