Fix register allocation bug in building use intervals.

runtime/vm/flow_graph_allocator.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/flow_graph_allocator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/intermediate_language.h"
 #include "vm/il_printer.h"
 #include "vm/flow_graph.h"
@@ skipping 246 matching lines @@
 void LiveRange::AddUseInterval(intptr_t start, intptr_t end) {
   ASSERT(start < end);
 
   // Live ranges are being build by visiting instructions in post-order.
   // This implies that use intervals will be prepended in a monotonically
   // decreasing order.
   if (first_use_interval() != NULL) {
     // If the first use interval and the use interval we are adding
     // touch then we can just extend the first interval to cover their
     // union.
-    if (start >= first_use_interval()->start()) {
+    if (start > first_use_interval()->start()) {
       // The only case when we can add intervals with start greater than
       // start of an already created interval is BlockLocation.
-      ASSERT((start == first_use_interval()->start()) ||
-             (vreg() == kNoVirtualRegister));
+      ASSERT(vreg() == kNoVirtualRegister);
       ASSERT(end <= first_use_interval()->end());
       return;
+    } else if (start == first_use_interval()->start()) {
+      // Grow first interval if necessary.
+      if (end <= first_use_interval()->end()) return;
+      first_use_interval_->end_ = end;
+      return;
     } else if (end == first_use_interval()->start()) {
       first_use_interval()->start_ = start;
       return;
     }
 
     ASSERT(end < first_use_interval()->start());
   }
 
   first_use_interval_ = new UseInterval(start, end, first_use_interval_);
   if (last_use_interval_ == NULL) {
@@ skipping 2317 matching lines @@
     OS::Print("-- [after ssa allocator] ir [%s] -------------\n",
               function.ToFullyQualifiedCString());
     FlowGraphPrinter printer(flow_graph_, true);
     printer.PrintBlocks();
     OS::Print("----------------------------------------------\n");
   }
 }
 
 
 }  // namespace dart