Simple redundant load elimination.

runtime/vm/bit_vector.cc

Index: runtime/vm/bit_vector.cc
===================================================================
--- runtime/vm/bit_vector.cc	(revision 12420)
+++ runtime/vm/bit_vector.cc	(working copy)
@@ -33,6 +33,14 @@
 }
 
 
+bool BitVector::Equals(const BitVector& other) const {
+  for (int i = 0; i < data_length_; i++) {
+    if (data_[i] != other.data_[i]) return false;
+  }
+  return true;
+}
+
+
 bool BitVector::AddAll(BitVector* from) {
   ASSERT(data_length_ == from->data_length_);
   bool changed = false;
@@ -60,4 +68,25 @@
 }
 
 
+bool BitVector::Intersect(const BitVector& other) {

[Kevin Millikin (Google), 2012/09/17 12:09:47]

It doesn't look like you use the return value, so we can use the simpler
implementation that doesn't care about changed.

[Florian Schneider, 2012/09/17 14:20:59]

Done.

+  ASSERT(other.length() == length());
+  bool changed = false;
+  for (int i = 0; i < data_length_; i++) {
+    const uword before = data_[i];
+    const uword after = data_[i] & other.data_[i];
+    if (before != after) changed = true;
+    data_[i] = after;
+  }
+  return changed;
+}
+
+
+void BitVector::Print() const {
+  OS::Print("[");
+  for (intptr_t i = 0; i < length_; i++) {
+    OS::Print(Contains(i) ? "1" : "0");
+  }
+  OS::Print("]");
+}
+
 }  // namespace dart