[turbofan] Eliminate unused effectful nodes during representation selection.

src/compiler/simplified-lowering.cc

 // Copyright 2014 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/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 743 matching lines @@
       EnqueueInput(node, i);  // Control inputs: just visit
     }
   }
 
   // The default, most general visitation case. For {node}, process all value,
   // context, frame state, effect, and control inputs, assuming that value
   // inputs should have {kRepTagged} representation and can observe all output
   // values {kTypeAny}.
   void VisitInputs(Node* node) {
     int tagged_count = node->op()->ValueInputCount() +
-                       OperatorProperties::GetContextInputCount(node->op());
-    // Visit value and context inputs as tagged.
+                       OperatorProperties::GetContextInputCount(node->op()) +
+                       OperatorProperties::GetFrameStateInputCount(node->op());
+    // Visit value, context and frame state inputs as tagged.
     for (int i = 0; i < tagged_count; i++) {
       ProcessInput(node, i, UseInfo::AnyTagged());
     }
-    // Only enqueue other inputs (framestates, effects, control).
+    // Only enqueue other inputs (effects, control).
     for (int i = tagged_count; i < node->InputCount(); i++) {
       EnqueueInput(node, i);
     }
   }
 
+  // Helper for an unused node.
+  void VisitUnused(Node* node) {
+    int value_count = node->op()->ValueInputCount();
+    for (int i = 0; i < value_count; i++) {
+      ProcessInput(node, i, UseInfo::None());
+    }
+    ProcessRemainingInputs(node, value_count);
+    if (lower()) Kill(node);
+  }
+
   // Helper for binops of the R x L -> O variety.
   void VisitBinop(Node* node, UseInfo left_use, UseInfo right_use,
                   MachineRepresentation output,
                   Type* restriction_type = Type::Any()) {
     DCHECK_EQ(2, node->op()->ValueInputCount());
     ProcessInput(node, 0, left_use);
     ProcessInput(node, 1, right_use);
     for (int i = 2; i < node->InputCount(); i++) {
       EnqueueInput(node, i);
     }
@@ skipping 142 matching lines @@
     // truncation truncation along.
     UseInfo input_use(output, truncation);
     for (int i = 0; i < node->InputCount(); i++) {
       ProcessInput(node, i, i < values ? input_use : UseInfo::None());
     }
   }
 
   void VisitCall(Node* node, SimplifiedLowering* lowering) {
     const CallDescriptor* desc = CallDescriptorOf(node->op());
     int params = static_cast<int>(desc->ParameterCount());
+    int value_input_count = node->op()->ValueInputCount();
     // Propagate representation information from call descriptor.
-    for (int i = 0; i < node->InputCount(); i++) {
+    for (int i = 0; i < value_input_count; i++) {
       if (i == 0) {
         // The target of the call.
-        ProcessInput(node, i, UseInfo::None());
+        ProcessInput(node, i, UseInfo::Any());
       } else if ((i - 1) < params) {
         ProcessInput(node, i, TruncatingUseInfoFromRepresentation(
                                   desc->GetInputType(i).representation()));
       } else {
-        ProcessInput(node, i, UseInfo::None());
+        ProcessInput(node, i, UseInfo::AnyTagged());
       }
     }
+    ProcessRemainingInputs(node, value_input_count);
 
     if (desc->ReturnCount() > 0) {
       SetOutput(node, desc->GetReturnType(0).representation());
     } else {
       SetOutput(node, MachineRepresentation::kTagged);
     }
   }
 
   MachineSemantic DeoptValueSemanticOf(Type* type) {
     // We only need signedness to do deopt correctly.
@@ skipping 143 matching lines @@
   void ChangeToInt32OverflowOp(Node* node) {
     NodeProperties::ChangeOp(node, Int32OverflowOp(node));
   }
 
   void ChangeToUint32OverflowOp(Node* node) {
     NodeProperties::ChangeOp(node, Uint32OverflowOp(node));
   }
 
   void VisitSpeculativeAdditiveOp(Node* node, Truncation truncation,
                                   SimplifiedLowering* lowering) {
+    if (truncation.IsUnused()) return VisitUnused(node);
     if (BothInputsAre(node, type_cache_.kSigned32OrMinusZero) &&
         NodeProperties::GetType(node)->Is(Type::Signed32())) {
       // int32 + int32 = int32   ==>   signed Int32Add/Sub
       VisitInt32Binop(node);
       if (lower()) ChangeToPureOp(node, Int32Op(node));
       return;
     }
 
     // Use truncation if available.
     if (BothInputsAre(node, type_cache_.kAdditiveSafeIntegerOrMinusZero) &&
@@ skipping 37 matching lines @@
     if (lower()) {
       ChangeToPureOp(node, Float64Op(node));
     }
     return;
   }
 
   // Dispatching routine for visiting the node {node} with the usage {use}.
   // Depending on the operator, propagate new usage info to the inputs.
   void VisitNode(Node* node, Truncation truncation,
                  SimplifiedLowering* lowering) {
+    // Unconditionally eliminate unused pure nodes (only relevant if there's
+    // a pure operation in between two effectful ones, where the last one
+    // is unused).
+    if (node->op()->HasProperty(Operator::kPure) && truncation.IsUnused()) {
+      return VisitUnused(node);
+    }
     switch (node->opcode()) {
       //------------------------------------------------------------------
       // Common operators.
       //------------------------------------------------------------------
       case IrOpcode::kStart:
+        return VisitLeaf(node, MachineRepresentation::kTagged);

[Jarin, 2016/07/21 08:23:09]

Comment why this is needed, please.

       case IrOpcode::kDead:
         return VisitLeaf(node, MachineRepresentation::kNone);
       case IrOpcode::kParameter: {
         // TODO(titzer): use representation from linkage.
         ProcessInput(node, 0, UseInfo::None());
         SetOutput(node, MachineRepresentation::kTagged);
         return;
       }
       case IrOpcode::kInt32Constant:
         return VisitLeaf(node, MachineRepresentation::kWord32);
@@ skipping 93 matching lines @@
         return;
       }
 
       case IrOpcode::kSpeculativeNumberAdd:
       case IrOpcode::kSpeculativeNumberSubtract:
         return VisitSpeculativeAdditiveOp(node, truncation, lowering);
 
       case IrOpcode::kSpeculativeNumberLessThan:
       case IrOpcode::kSpeculativeNumberLessThanOrEqual:
       case IrOpcode::kSpeculativeNumberEqual: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         // Number comparisons reduce to integer comparisons for integer inputs.
         if (TypeOf(node->InputAt(0))->Is(Type::Unsigned32()) &&
             TypeOf(node->InputAt(1))->Is(Type::Unsigned32())) {
           // => unsigned Int32Cmp
           VisitUint32Cmp(node);
           if (lower()) ChangeToPureOp(node, Uint32Op(node));
           return;
         } else if (TypeOf(node->InputAt(0))->Is(Type::Signed32()) &&
                    TypeOf(node->InputAt(1))->Is(Type::Signed32())) {
           // => signed Int32Cmp
@@ skipping 34 matching lines @@
           VisitWord32TruncatingBinop(node);
           if (lower()) NodeProperties::ChangeOp(node, Int32Op(node));
         } else {
           // => Float64Add/Sub
           VisitFloat64Binop(node);
           if (lower()) NodeProperties::ChangeOp(node, Float64Op(node));
         }
         return;
       }
       case IrOpcode::kSpeculativeNumberMultiply: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         if (BothInputsAre(node, Type::Integral32()) &&
             (NodeProperties::GetType(node)->Is(Type::Signed32()) ||
              NodeProperties::GetType(node)->Is(Type::Unsigned32()) ||
              (truncation.TruncatesToWord32() &&
               NodeProperties::GetType(node)->Is(
                   type_cache_.kSafeIntegerOrMinusZero)))) {
           // Multiply reduces to Int32Mul if the inputs are integers, and
           // (a) the output is either known to be Signed32, or
           // (b) the output is known to be Unsigned32, or
           // (c) the uses are truncating and the result is in the safe
@@ skipping 54 matching lines @@
           VisitWord32TruncatingBinop(node);
           if (lower()) ChangeToPureOp(node, Int32Op(node));
           return;
         }
         // Number x Number => Float64Mul
         VisitFloat64Binop(node);
         if (lower()) ChangeToPureOp(node, Float64Op(node));
         return;
       }
       case IrOpcode::kSpeculativeNumberDivide: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         if (BothInputsAreUnsigned32(node) && truncation.TruncatesToWord32()) {
           // => unsigned Uint32Div
           VisitWord32TruncatingBinop(node);
           if (lower()) DeferReplacement(node, lowering->Uint32Div(node));
           return;
         }
         if (BothInputsAreSigned32(node)) {
           if (NodeProperties::GetType(node)->Is(Type::Signed32())) {
           // => signed Int32Div
           VisitInt32Binop(node);
@@ skipping 85 matching lines @@
           return;
         }
         // Checked float64 x float64 => float64
         DCHECK_EQ(IrOpcode::kSpeculativeNumberDivide, node->opcode());
         VisitBinop(node, UseInfo::CheckedNumberOrOddballAsFloat64(),
                    MachineRepresentation::kFloat64, Type::Number());
         if (lower()) ChangeToPureOp(node, Float64Op(node));
         return;
       }
       case IrOpcode::kSpeculativeNumberModulus: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         if (BothInputsAreUnsigned32(node) && truncation.TruncatesToWord32()) {
           // => unsigned Uint32Mod
           VisitWord32TruncatingBinop(node);
           if (lower()) DeferReplacement(node, lowering->Uint32Mod(node));
           return;
         }
         if (BothInputsAreSigned32(node)) {
           if (NodeProperties::GetType(node)->Is(Type::Signed32())) {
             // => signed Int32Mod
             VisitInt32Binop(node);
@@ skipping 93 matching lines @@
       case IrOpcode::kNumberShiftLeft: {
         Type* rhs_type = GetUpperBound(node->InputAt(1));
         VisitBinop(node, UseInfo::TruncatingWord32(),
                    UseInfo::TruncatingWord32(), MachineRepresentation::kWord32);
         if (lower()) {
           lowering->DoShift(node, lowering->machine()->Word32Shl(), rhs_type);
         }
         return;
       }
       case IrOpcode::kSpeculativeNumberShiftLeft: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         if (BothInputsAre(node, Type::NumberOrOddball())) {
           Type* rhs_type = GetUpperBound(node->InputAt(1));
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
           if (lower()) {
             lowering->DoShift(node, lowering->machine()->Word32Shl(), rhs_type);
           }
           return;
         }
@@ skipping 291 matching lines @@
         return;
       }
 
       case IrOpcode::kAllocate: {
         ProcessInput(node, 0, UseInfo::TruncatingWord32());
         ProcessRemainingInputs(node, 1);
         SetOutput(node, MachineRepresentation::kTagged);
         return;
       }
       case IrOpcode::kLoadField: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         FieldAccess access = FieldAccessOf(node->op());
-        MachineRepresentation representation =
+        MachineRepresentation const representation =
             access.machine_type.representation();
         // If we are loading from a Smi field and truncate the result to Word32,
         // we can instead just load the high word on 64-bit architectures, which
         // is exactly the Word32 we are looking for, and therefore avoid a nasty
         // right shift afterwards.
         // TODO(bmeurer): Introduce an appropriate tagged-signed machine rep.
         if (truncation.TruncatesToWord32() &&
             representation == MachineRepresentation::kTagged &&
             access.type->Is(Type::TaggedSigned()) && SmiValuesAre32Bits()) {
           VisitUnop(node, UseInfoForBasePointer(access),
@@ skipping 26 matching lines @@
         if (lower()) {
           if (write_barrier_kind < access.write_barrier_kind) {
             access.write_barrier_kind = write_barrier_kind;
             NodeProperties::ChangeOp(
                 node, jsgraph_->simplified()->StoreField(access));
           }
         }
         return;
       }
       case IrOpcode::kLoadBuffer: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         BufferAccess access = BufferAccessOf(node->op());
         ProcessInput(node, 0, UseInfo::PointerInt());        // buffer
         ProcessInput(node, 1, UseInfo::TruncatingWord32());  // offset
         ProcessInput(node, 2, UseInfo::TruncatingWord32());  // length
         ProcessRemainingInputs(node, 3);
 
         MachineRepresentation output;
         if (truncation.TruncatesUndefinedToZeroOrNaN()) {
           if (truncation.TruncatesNaNToZero()) {
             // If undefined is truncated to a non-NaN number, we can use
@@ skipping 26 matching lines @@
         ProcessInput(node, 2, UseInfo::TruncatingWord32());  // length
         ProcessInput(node, 3,
                      TruncatingUseInfoFromRepresentation(
                          access.machine_type().representation()));  // value
         ProcessRemainingInputs(node, 4);
         SetOutput(node, MachineRepresentation::kNone);
         if (lower()) lowering->DoStoreBuffer(node);
         return;
       }
       case IrOpcode::kLoadElement: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         ElementAccess access = ElementAccessOf(node->op());
-        ProcessInput(node, 0, UseInfoForBasePointer(access));  // base
-        ProcessInput(node, 1, UseInfo::TruncatingWord32());    // index
-        ProcessRemainingInputs(node, 2);
-        SetOutput(node, access.machine_type.representation());
+        VisitBinop(node, UseInfoForBasePointer(access),
+                    UseInfo::TruncatingWord32(),
+                    access.machine_type.representation());
         return;
       }
       case IrOpcode::kStoreElement: {
         ElementAccess access = ElementAccessOf(node->op());
         WriteBarrierKind write_barrier_kind = WriteBarrierKindFor(
             access.base_is_tagged, access.machine_type.representation(),
             access.type, node->InputAt(2));
         ProcessInput(node, 0, UseInfoForBasePointer(access));  // base
         ProcessInput(node, 1, UseInfo::TruncatingWord32());    // index
         ProcessInput(node, 2,
@@ skipping 52 matching lines @@
       case IrOpcode::kObjectIsNumber:
       case IrOpcode::kObjectIsReceiver:
       case IrOpcode::kObjectIsSmi:
       case IrOpcode::kObjectIsString:
       case IrOpcode::kObjectIsUndetectable: {
         ProcessInput(node, 0, UseInfo::AnyTagged());
         SetOutput(node, MachineRepresentation::kBit);
         return;
       }
       case IrOpcode::kCheckFloat64Hole: {
+        if (truncation.IsUnused()) return VisitUnused(node);
         CheckFloat64HoleMode mode = CheckFloat64HoleModeOf(node->op());
         ProcessInput(node, 0, UseInfo::TruncatingFloat64());
         ProcessRemainingInputs(node, 1);
         SetOutput(node, MachineRepresentation::kFloat64);
         if (truncation.TruncatesToFloat64() &&
             mode == CheckFloat64HoleMode::kAllowReturnHole) {
           if (lower()) DeferReplacement(node, node->InputAt(0));
         }
         return;
       }
@@ skipping 216 matching lines @@
     } else {
       DCHECK_EQ(0, node->op()->ControlInputCount());
     }
 
     replacements_.push_back(node);
     replacements_.push_back(replacement);
 
     node->NullAllInputs();  // Node is now dead.
   }
 
+  void Kill(Node* node) {
+    TRACE("killing #%d:%s\n", node->id(), node->op()->mnemonic());
+
+    if (node->op()->EffectInputCount() == 1) {
+      DCHECK_LT(0, node->op()->ControlInputCount());
+      // Disconnect the node from effect and control chains.
+      Node* control = NodeProperties::GetControlInput(node);
+      Node* effect = NodeProperties::GetEffectInput(node);
+      ReplaceEffectControlUses(node, effect, control);
+    } else {
+      DCHECK_EQ(0, node->op()->ControlInputCount());
+      DCHECK_EQ(0, node->op()->EffectInputCount());
+      DCHECK_EQ(0, node->op()->ControlOutputCount());
+      DCHECK_EQ(0, node->op()->EffectOutputCount());
+    }
+
+    node->ReplaceUses(jsgraph_->Dead());
+
+    node->NullAllInputs();  // The {node} is now dead.
+  }
+
   void PrintOutputInfo(NodeInfo* info) {
     if (FLAG_trace_representation) {
       OFStream os(stdout);
       os << info->representation();
     }
   }
 
   void PrintRepresentation(MachineRepresentation rep) {
     if (FLAG_trace_representation) {
       OFStream os(stdout);
@@ skipping 1018 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8