[turbofan] Use bounds checks to eliminate subsequent inc/dec overflow checks.

src/compiler/redundancy-elimination.cc

Index: src/compiler/redundancy-elimination.cc
diff --git a/src/compiler/redundancy-elimination.cc b/src/compiler/redundancy-elimination.cc
index 6dcf2bf4cf0c111da9c018c0feb8e946d22ad061..acd051ac4408bb2b0d4bd05bba4166752e13d306 100644
--- a/src/compiler/redundancy-elimination.cc
+++ b/src/compiler/redundancy-elimination.cc
@@ -36,6 +36,11 @@ Reduction RedundancyElimination::Reduce(Node* node) {
     case IrOpcode::kCheckedTaggedToInt32:
     case IrOpcode::kCheckedUint32ToInt32:
       return ReduceCheckNode(node);
+    case IrOpcode::kSpeculativeNumberAdd:
+    case IrOpcode::kSpeculativeNumberSubtract:
+      // For increments and decrements by a constant, try to learn from the last
+      // bounds check.
+      return TryReuseBoundsCheckForFirstInput(node);
     case IrOpcode::kEffectPhi:
       return ReduceEffectPhi(node);
     case IrOpcode::kDead:
@@ -133,6 +138,17 @@ Node* RedundancyElimination::EffectPathChecks::LookupCheck(Node* node) const {
   return nullptr;
 }
 
+Node* RedundancyElimination::EffectPathChecks::LookupBoundsCheckFor(
+    Node* node) const {
+  for (Check const* check = head_; check != nullptr; check = check->next) {
+    if (check->node->opcode() == IrOpcode::kCheckBounds &&
+        check->node->InputAt(0) == node) {
+      return check->node;
+    }
+  }
+  return nullptr;
+}
+
 RedundancyElimination::EffectPathChecks const*
 RedundancyElimination::PathChecksForEffectNodes::Get(Node* node) const {
   size_t const id = node->id();
@@ -158,10 +174,41 @@ Reduction RedundancyElimination::ReduceCheckNode(Node* node) {
     ReplaceWithValue(node, check);
     return Replace(check);
   }
+
   // Learn from this check.
   return UpdateChecks(node, checks->AddCheck(zone(), node));
 }
 
+Reduction RedundancyElimination::TryReuseBoundsCheckForFirstInput(Node* node) {
+  DCHECK(node->opcode() == IrOpcode::kSpeculativeNumberAdd ||
+         node->opcode() == IrOpcode::kSpeculativeNumberSubtract);
+
+  DCHECK_EQ(1, node->op()->EffectInputCount());
+  DCHECK_EQ(1, node->op()->EffectOutputCount());
+
+  Node* const effect = NodeProperties::GetEffectInput(node);
+  EffectPathChecks const* checks = node_checks_.Get(effect);
+
+  // 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 (checks == nullptr) return NoChange();
+
+  Node* left = node->InputAt(0);
+  Node* right = node->InputAt(1);
+  // Only use bounds checks for increments/decrements by a constant.
+  if (right->opcode() == IrOpcode::kNumberConstant) {
+    if (Node* bounds_check = checks->LookupBoundsCheckFor(left)) {
+      // Only use the bounds checked type if it is better.
+      if (NodeProperties::GetType(bounds_check)
+              ->Is(NodeProperties::GetType(left))) {
+        node->ReplaceInput(0, bounds_check);
+      }
+    }
+  }
+
+  return UpdateChecks(node, checks);
+}
+
 Reduction RedundancyElimination::ReduceEffectPhi(Node* node) {
   Node* const control = NodeProperties::GetControlInput(node);
   if (control->opcode() == IrOpcode::kLoop) {