[turbofan] Eliminate a few redundant bounds checks.

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 74 matching lines @@
   bool condition_is_true = node->opcode() == IrOpcode::kDeoptimizeUnless;
   Node* condition = NodeProperties::GetValueInput(node, 0);
   Node* frame_state = NodeProperties::GetValueInput(node, 1);
   Node* effect = NodeProperties::GetEffectInput(node);
   Node* control = NodeProperties::GetControlInput(node);
   ControlPathConditions const* conditions = node_conditions_.Get(control);
   // If we do not know anything about the predecessor, do not propagate just
   // yet because we will have to recompute anyway once we compute the
   // predecessor.
   if (conditions == nullptr) {
-    DCHECK_NULL(node_conditions_.Get(node));
-    return NoChange();
+    return UpdateConditions(node, conditions);
   }
   Maybe<bool> condition_value = conditions->LookupCondition(condition);
   if (condition_value.IsJust()) {
     // If we know the condition we can discard the branch.
     if (condition_is_true == condition_value.FromJust()) {
       // We don't update the conditions here, because we're replacing {node}
       // with the {control} node that already contains the right information.
       ReplaceWithValue(node, dead(), effect, control);
     } else {
       control = graph()->NewNode(common()->Deoptimize(DeoptimizeKind::kEager),
                                  frame_state, effect, control);
       // TODO(bmeurer): This should be on the AdvancedReducer somehow.
       NodeProperties::MergeControlToEnd(graph(), common(), control);
       Revisit(graph()->end());
     }
     return Replace(dead());
   }
   return UpdateConditions(
       node, conditions->AddCondition(zone_, condition, condition_is_true));
 }
 
 Reduction BranchElimination::ReduceIf(Node* node, bool is_true_branch) {
   // Add the condition to the list arriving from the input branch.
   Node* branch = NodeProperties::GetControlInput(node, 0);
   const ControlPathConditions* from_branch = node_conditions_.Get(branch);
   // If we do not know anything about the predecessor, do not propagate just
   // yet because we will have to recompute anyway once we compute the
   // predecessor.
   if (from_branch == nullptr) {
-    DCHECK(node_conditions_.Get(node) == nullptr);
-    return NoChange();
+    return UpdateConditions(node, nullptr);
   }
   Node* condition = branch->InputAt(0);
   return UpdateConditions(
       node, from_branch->AddCondition(zone_, condition, is_true_branch));
 }
 
 
 Reduction BranchElimination::ReduceLoop(Node* node) {
   // 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 (int i = 0; i < node->InputCount(); i++) {
     if (node_conditions_.Get(node->InputAt(i)) == nullptr) {
-      DCHECK(node_conditions_.Get(node) == nullptr);
-      return NoChange();
+      return UpdateConditions(node, nullptr);
     }
   }
 
   const ControlPathConditions* first = node_conditions_.Get(node->InputAt(0));
   // 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++) {
@@ skipping 42 matching lines @@
   return UpdateConditions(node, from_input);
 }
 
 
 Reduction BranchElimination::UpdateConditions(
     Node* node, const ControlPathConditions* conditions) {
   const ControlPathConditions* original = node_conditions_.Get(node);
   // Only signal that the node has Changed if the condition information has
   // changed.
   if (conditions != original) {
-    if (original == nullptr || *conditions != *original) {
+    if (conditions == nullptr || original == nullptr ||
+        *conditions != *original) {
       node_conditions_.Set(node, conditions);
       return Changed(node);
     }
   }
   return NoChange();
 }
 
 
 // static
 const BranchElimination::ControlPathConditions*
@@ skipping 81 matching lines @@
 
 Graph* BranchElimination::graph() const { return jsgraph()->graph(); }
 
 CommonOperatorBuilder* BranchElimination::common() const {
   return jsgraph()->common();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8