Use range analysis to improve constant propagation.

runtime/vm/intermediate_language.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 590 matching lines @@
     UnuseAllInputs();
   }
   set_previous(NULL);
   set_next(NULL);
 }
 
 
 BranchInstr::BranchInstr(ComparisonInstr* comparison, bool is_checked)
     : comparison_(comparison),
       is_checked_(is_checked),
-      constrained_type_(NULL) {
+      constrained_type_(NULL),
+      constant_target_(NULL) {
   for (intptr_t i = comparison->InputCount() - 1; i >= 0; --i) {
     comparison->InputAt(i)->set_instruction(this);
   }
 }
 
 
 void BranchInstr::RawSetInputAt(intptr_t i, Value* value) {
   comparison()->RawSetInputAt(i, value);
 }
 
@@ skipping 1563 matching lines @@
 
 
 // Inclusive.
 bool Range::IsWithin(intptr_t min_int, intptr_t max_int) const {
   if (min().LowerBound().value() < min_int) return false;
   if (max().UpperBound().value() > max_int) return false;
   return true;
 }
 
 
+bool Range::IsUnsatisfiable() const {
+  // Constant case: For example [0, -1].
+  if (Range::ConstantMin(this).value() > Range::ConstantMax(this).value()) {
+    return true;
+  }
+  // Symbol case: For example [v+1, v].
+  if (DependOnSameSymbol(min(), max()) && min().offset() > max().offset()) {
+    return true;
+  }
+  return false;
+}
+
+
 bool CheckArrayBoundInstr::IsFixedLengthArrayType(intptr_t cid) {
   return LoadFieldInstr::IsFixedLengthArrayCid(cid);
 }
 
 
 bool CheckArrayBoundInstr::IsRedundant(RangeBoundary length) {
   // Check that array has an immutable length.
   if (!IsFixedLengthArrayType(array_type())) {
     return false;
   }
@@ skipping 135 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart