[turbofan] Improve testability of the InstructionSelector.

src/compiler/instruction-selector.h

Index: src/compiler/instruction-selector.h
diff --git a/src/compiler/instruction-selector.h b/src/compiler/instruction-selector.h
index b6c7039aefd709d5c0f21d438bd3832756a5d947..015879f8603e394f73bfc50fab0843824dedff32 100644
--- a/src/compiler/instruction-selector.h
+++ b/src/compiler/instruction-selector.h
@@ -22,8 +22,12 @@ class FlagsContinuation;
 
 class InstructionSelector V8_FINAL {
  public:
-  explicit InstructionSelector(InstructionSequence* sequence,
-                               SourcePositionTable* source_positions);
+  // Forward declarations.
+  class Features;
+
+  InstructionSelector(InstructionSequence* sequence,
+                      SourcePositionTable* source_positions,
+                      Features features = SupportedFeatures());
 
   // Visit code for the entire graph with the included schedule.
   void SelectInstructions();
@@ -54,6 +58,32 @@ class InstructionSelector V8_FINAL {
                     InstructionOperand* *temps = NULL);
   Instruction* Emit(Instruction* instr);
 
+  // ===========================================================================
+  // ============== Architecture-independent CPU feature methods. ==============
+  // ===========================================================================
+
+  class Features V8_FINAL {
+   public:
+    Features() : bits_(0) {}
+    explicit Features(unsigned bits) : bits_(bits) {}
+    explicit Features(CpuFeature f) : bits_(1u << f) {}
+    Features(CpuFeature f1, CpuFeature f2) : bits_((1u << f1) | (1u << f2)) {}
+
+    bool Contains(CpuFeature f) const { return (bits_ & (1u << f)); }
+
+   private:
+    unsigned bits_;
+  };
+
+  bool IsSupported(CpuFeature feature) const {
+    return features_.Contains(feature);
+  }
+
+  // Returns the features supported on the target platform.
+  static Features SupportedFeatures() {
+    return Features(CpuFeatures::SupportedFeatures());
+  }
+
  private:
   friend class OperandGenerator;
 
@@ -168,6 +198,7 @@ class InstructionSelector V8_FINAL {
   Zone zone_;
   InstructionSequence* sequence_;
   SourcePositionTable* source_positions_;
+  Features features_;
   BasicBlock* current_block_;
   Instructions instructions_;
   BoolVector defined_;