[x64] Improve instruction selection for TruncateInt64ToInt32.

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 <algorithm>
 
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 794 matching lines @@
   X64OperandGenerator g(this);
   Emit(kSSECvtsd2ss, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
 }
 
 
 void InstructionSelector::VisitTruncateInt64ToInt32(Node* node) {
   X64OperandGenerator g(this);
   Node* value = node->InputAt(0);
   if (CanCover(node, value)) {
     switch (value->opcode()) {
-      case IrOpcode::kWord64Sar:
-      case IrOpcode::kWord64Shr: {
+      case IrOpcode::kWord64Sar: {
         Int64BinopMatcher m(value);
-        if (m.right().Is(32)) {
+        if (m.right().IsInRange(1, 32)) {
           Emit(kX64Shr, g.DefineSameAsFirst(node),
-               g.UseRegister(m.left().node()), g.TempImmediate(32));
+               g.UseRegister(m.left().node()),
+               g.UseImmediate(m.right().node()));
           return;
         }
         break;
+      }
+      case IrOpcode::kWord64Shl: {
+        Int64BinopMatcher m(value);
+        if (m.right().IsInRange(1, 31)) {
+          Emit(kX64Shl32, g.DefineSameAsFirst(node),
+               g.UseRegister(m.left().node()),
+               g.UseImmediate(m.right().node()));
+          return;
+        }
+        break;
       }
       default:
         break;
     }
   }
-  Emit(kX64Movl, g.DefineAsRegister(node), g.Use(value));
+  // Otherwise truncation from 64-bit to 32-bit is a no-nop, as 32-bit
+  // operations just ignore the upper 64-bit.
+  Emit(kArchNop, g.DefineAsRegister(node), g.Use(value));
 }
 
 
 void InstructionSelector::VisitFloat64Add(Node* node) {
   X64OperandGenerator g(this);
   if (IsSupported(AVX)) {
     Emit(kAVXFloat64Add, g.DefineAsRegister(node),
          g.UseRegister(node->InputAt(0)), g.Use(node->InputAt(1)));
   } else {
     Emit(kSSEFloat64Add, g.DefineSameAsFirst(node),
@@ skipping 545 matching lines @@
            MachineOperatorBuilder::kFloat64Ceil |
            MachineOperatorBuilder::kFloat64RoundTruncate |
            MachineOperatorBuilder::kWord32ShiftIsSafe;
   }
   return MachineOperatorBuilder::kNoFlags;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8