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

This has two parts:
- in redundancy elimination, if we see addition with left hand side that
  was bounds-checked, we reconnect the lhs to the bounds check if it has better
  type.
- in representation inference, eliminate overflow checks if the input types
  guarantee no overflow.

Review-Url: https://codereview.chromium.org/2527083002
Cr-Commit-Position: refs/heads/master@{#41260}

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) {

src/compiler/redundancy-elimination.h

@@ -34,6 +34,7 @@ class RedundancyElimination final : public AdvancedReducer {
 
     EffectPathChecks const* AddCheck(Zone* zone, Node* node) const;
     Node* LookupCheck(Node* node) const;
+    Node* LookupBoundsCheckFor(Node* node) const;
 
    private:
     EffectPathChecks(Check* head, size_t size) : head_(head), size_(size) {}
@@ -62,6 +63,8 @@ class RedundancyElimination final : public AdvancedReducer {
   Reduction TakeChecksFromFirstEffect(Node* node);
   Reduction UpdateChecks(Node* node, EffectPathChecks const* checks);
 
+  Reduction TryReuseBoundsCheckForFirstInput(Node* node);
+
   Zone* zone() const { return zone_; }
 
   PathChecksForEffectNodes node_checks_;

src/compiler/simplified-lowering.cc

@@ -209,8 +209,30 @@ class InputUseInfos {
 
 #endif  // DEBUG
 
-}  // namespace
+bool CanOverflowSigned32(const Operator* op, Type* left, Type* right,
+                         Zone* type_zone) {
+  // We assume the inputs are checked Signed32 (or known statically
+  // to be Signed32). Technically, theinputs could also be minus zero, but
+  // that cannot cause overflow.
+  left = Type::Intersect(left, Type::Signed32(), type_zone);
+  right = Type::Intersect(right, Type::Signed32(), type_zone);
+  if (!left->IsInhabited() || !right->IsInhabited()) return false;
+  switch (op->opcode()) {
+    case IrOpcode::kSpeculativeNumberAdd:
+      return (left->Max() + right->Max() > kMaxInt) ||
+             (left->Min() + right->Min() < kMinInt);
 
+    case IrOpcode::kSpeculativeNumberSubtract:
+      return (left->Max() - right->Min() > kMaxInt) ||
+             (left->Min() - right->Max() < kMinInt);
+
+    default:
+      UNREACHABLE();
+  }
+  return true;
+}
+
+}  // namespace
 
 class RepresentationSelector {
  public:
@@ -1164,6 +1186,7 @@ class RepresentationSelector {
     if (BothInputsAre(node, Type::PlainPrimitive())) {
       if (truncation.IsUnused()) return VisitUnused(node);
     }
+
     if (BothInputsAre(node, type_cache_.kAdditiveSafeIntegerOrMinusZero) &&
         (GetUpperBound(node)->Is(Type::Signed32()) ||
          GetUpperBound(node)->Is(Type::Unsigned32()) ||
@@ -1177,23 +1200,20 @@ class RepresentationSelector {
     // Try to use type feedback.
     NumberOperationHint hint = NumberOperationHintOf(node->op());
 
-    // Handle the case when no int32 checks on inputs are necessary
-    // (but an overflow check is needed on the output).
-    if (BothInputsAre(node, Type::Signed32()) ||
-        (BothInputsAre(node, Type::Signed32OrMinusZero()) &&
-         NodeProperties::GetType(node)->Is(type_cache_.kSafeInteger))) {
-      // If both the inputs the feedback are int32, use the overflow op.
     if (hint == NumberOperationHint::kSignedSmall ||
         hint == NumberOperationHint::kSigned32) {
+      Type* left_feedback_type = TypeOf(node->InputAt(0));
+      Type* right_feedback_type = TypeOf(node->InputAt(1));
+      // Handle the case when no int32 checks on inputs are necessary (but
+      // an overflow check is needed on the output).
+      // TODO(jarin) We should not look at the upper bound because the typer
+      // could have already baked in some feedback into the upper bound.
+      if (BothInputsAre(node, Type::Signed32()) ||
+          (BothInputsAre(node, Type::Signed32OrMinusZero()) &&
+           GetUpperBound(node)->Is(type_cache_.kSafeInteger))) {
         VisitBinop(node, UseInfo::TruncatingWord32(),
                    MachineRepresentation::kWord32, Type::Signed32());
-        if (lower()) ChangeToInt32OverflowOp(node);
-        return;
-      }
-    }
-
-    if (hint == NumberOperationHint::kSignedSmall ||
-        hint == NumberOperationHint::kSigned32) {
+      } else {
         UseInfo left_use = CheckedUseInfoAsWord32FromHint(hint);
         // For CheckedInt32Add and CheckedInt32Sub, we don't need to do
         // a minus zero check for the right hand side, since we already
@@ -1203,7 +1223,15 @@ class RepresentationSelector {
             hint, CheckForMinusZeroMode::kDontCheckForMinusZero);
         VisitBinop(node, left_use, right_use, MachineRepresentation::kWord32,
                    Type::Signed32());
-      if (lower()) ChangeToInt32OverflowOp(node);
+      }
+      if (lower()) {
+        if (CanOverflowSigned32(node->op(), left_feedback_type,
+                                right_feedback_type, graph_zone())) {
+          ChangeToInt32OverflowOp(node);
+        } else {
+          ChangeToPureOp(node, Int32Op(node));
+        }
+      }
       return;
     }