Improved range analysis for bitwise operations.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
===================================================================
--- src/hydrogen-instructions.h	(revision 15052)
+++ src/hydrogen-instructions.h	(working copy)
@@ -43,6 +43,7 @@
 namespace internal {
 
 // Forward declarations.
+class BitRange;
 class HBasicBlock;
 class HEnvironment;
 class HInferRepresentation;
@@ -258,7 +259,7 @@
     result->set_can_be_minus_zero(CanBeMinusZero());
     return result;
   }
-  int32_t Mask() const;
+  void ToBitRange(BitRange* bits) const;
   void set_can_be_minus_zero(bool b) { can_be_minus_zero_ = b; }
   bool CanBeMinusZero() const { return CanBeZero() && can_be_minus_zero_; }
   bool CanBeZero() const { return upper_ >= 0 && lower_ <= 0; }
@@ -305,6 +306,60 @@
 };
 
 
+class BitRange {
+ public:
+  BitRange() : known_(0), bits_(0) { }
+  BitRange(int32_t known, int32_t bits)
+      : known_(known), bits_(bits & known) { }
+
+  static void SetFromRange(BitRange* bits, int32_t lower, int32_t upper) {
+    // Find a mask for the most significant bits that are the same for all
+    // values in the range.
+    int32_t same = ~(lower ^ upper);
+    // Flood zeros to any bits lower than the most significant zero.
+    same &= (same >> 1);
+    same &= (same >> 2);
+    same &= (same >> 4);
+    same &= (same >> 8);
+    same &= (same >> 16);
+
+    bits->known_ = same;
+    bits->bits_ = lower & same;
+  }
+
+  void ExtendRange(int32_t* lower, int32_t* upper) const {
+    int32_t limit1 = (~known_ & 0x80000000) | bits_;
+    int32_t limit2 = (~known_ & 0x7fffffff) | bits_;
+    *lower = Min(*lower, Min(limit1, limit2));
+    *upper = Max(*upper, Max(limit1, limit2));
+  }
+
+  static BitRange And(BitRange a, BitRange b) {
+    int32_t known = a.known_ & b.known_;
+    // Zeros in either operand become known.
+    known |= (a.known_ & ~a.bits_);
+    known |= (b.known_ & ~b.bits_);
+    return BitRange(known, a.bits_ & b.bits_);
+  }
+
+  static BitRange Or(BitRange a, BitRange b) {
+    int32_t known = a.known_ & b.known_;
+    // Ones in either operand become known.
+    known |= (a.known_ & a.bits_);
+    known |= (b.known_ & b.bits_);
+    return BitRange(known, a.bits_ | b.bits_);
+  }
+
+  static BitRange Xor(BitRange a, BitRange b) {
+    return BitRange(a.known_ & b.known_, a.bits_ ^ b.bits_);
+  }
+
+ private:
+  int32_t known_;  // A mask of known bits.
+  int32_t bits_;   // Values of known bits, zero elsewhere.
+};
+
+
 class UniqueValueId {
  public:
   UniqueValueId() : raw_address_(NULL) { }