[turbofan] Improve code generation for inline comparisons with zero.

src/compiler/x64/instruction-selector-x64.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/generic-node-inl.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 803 matching lines @@
   } else if (g.CanBeImmediate(left)) {
     if (!node->op()->HasProperty(Operator::kCommutative)) cont->Commute();
     VisitCompare(selector, opcode, g.Use(right), g.UseImmediate(left), cont);
   } else {
     VisitCompare(selector, opcode, left, right, cont,
                  node->op()->HasProperty(Operator::kCommutative));
   }
 }
 
 
+// Shared routine for comparison with zero.
+static void VisitCompareZero(InstructionSelector* selector, Node* node,
+                             InstructionCode opcode, FlagsContinuation* cont) {
+  X64OperandGenerator g(selector);
+  VisitCompare(selector, opcode, g.Use(node), g.TempImmediate(0), cont);
+}
+
+
 // Shared routine for multiple float64 compare operations.
 static void VisitFloat64Compare(InstructionSelector* selector, Node* node,
                                 FlagsContinuation* cont) {
   VisitCompare(selector, kSSEFloat64Cmp, node->InputAt(0), node->InputAt(1),
                cont, node->op()->HasProperty(Operator::kCommutative));
 }
 
 
 void InstructionSelector::VisitBranch(Node* branch, BasicBlock* tbranch,
                                       BasicBlock* fbranch) {
@@ skipping 105 matching lines @@
       case IrOpcode::kWord32And:
         return VisitWordCompare(this, value, kX64Test32, &cont);
       case IrOpcode::kWord64And:
         return VisitWordCompare(this, value, kX64Test, &cont);
       default:
         break;
     }
   }
 
   // Branch could not be combined with a compare, emit compare against 0.
-  VisitCompare(this, kX64Cmp32, g.Use(value), g.TempImmediate(0), &cont);
+  VisitCompareZero(this, value, kX64Cmp32, &cont);
 }
 
 
 void InstructionSelector::VisitWord32Equal(Node* const node) {
-  Node* const user = node;
+  Node* user = node;
   FlagsContinuation cont(kEqual, node);
   Int32BinopMatcher m(user);
   if (m.right().Is(0)) {
-    Node* const value = m.left().node();
+    Node* value = m.left().node();
+
+    // Try to combine with comparisons against 0 by simply inverting the branch.
+    while (CanCover(user, value) && value->opcode() == IrOpcode::kWord32Equal) {
+      Int32BinopMatcher m(value);
+      if (m.right().Is(0)) {
+        user = value;
+        value = m.left().node();
+        cont.Negate();
+      } else {
+        break;
+      }
+    }
+
+    // Try to combine the branch with a comparison.
     if (CanCover(user, value)) {
       switch (value->opcode()) {
         case IrOpcode::kInt32Sub:
           return VisitWordCompare(this, value, kX64Cmp32, &cont);
         case IrOpcode::kWord32And:
           return VisitWordCompare(this, value, kX64Test32, &cont);
         default:
           break;
       }
     }
+    return VisitCompareZero(this, value, kX64Cmp32, &cont);
   }
   VisitWordCompare(this, node, kX64Cmp32, &cont);
 }
 
 
 void InstructionSelector::VisitInt32LessThan(Node* node) {
   FlagsContinuation cont(kSignedLessThan, node);
   VisitWordCompare(this, node, kX64Cmp32, &cont);
 }
 
@@ skipping 10 matching lines @@
 }
 
 
 void InstructionSelector::VisitUint32LessThanOrEqual(Node* node) {
   FlagsContinuation cont(kUnsignedLessThanOrEqual, node);
   VisitWordCompare(this, node, kX64Cmp32, &cont);
 }
 
 
 void InstructionSelector::VisitWord64Equal(Node* const node) {
-  Node* const user = node;
+  Node* user = node;
   FlagsContinuation cont(kEqual, node);
   Int64BinopMatcher m(user);
   if (m.right().Is(0)) {
-    Node* const value = m.left().node();
+    Node* value = m.left().node();
+
+    // Try to combine with comparisons against 0 by simply inverting the branch.
+    while (CanCover(user, value) && value->opcode() == IrOpcode::kWord64Equal) {
+      Int64BinopMatcher m(value);
+      if (m.right().Is(0)) {
+        user = value;
+        value = m.left().node();
+        cont.Negate();
+      } else {
+        break;
+      }
+    }
+
+    // Try to combine the branch with a comparison.
     if (CanCover(user, value)) {
       switch (value->opcode()) {
         case IrOpcode::kInt64Sub:
           return VisitWordCompare(this, value, kX64Cmp, &cont);
         case IrOpcode::kWord64And:
           return VisitWordCompare(this, value, kX64Test, &cont);
         default:
           break;
       }
     }
+    return VisitCompareZero(this, value, kX64Cmp, &cont);
   }
   VisitWordCompare(this, node, kX64Cmp, &cont);
 }
 
 
 void InstructionSelector::VisitInt32AddWithOverflow(Node* node) {
   if (Node* ovf = node->FindProjection(1)) {
     FlagsContinuation cont(kOverflow, ovf);
     VisitBinop(this, node, kX64Add32, &cont);
   }
@@ skipping 43 matching lines @@
 
 
 void InstructionSelector::VisitFloat64LessThanOrEqual(Node* node) {
   FlagsContinuation cont(kUnorderedLessThanOrEqual, node);
   VisitFloat64Compare(this, node, &cont);
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8