Fix broken use lists in branch instructions.

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 552 matching lines @@
     other->LinkTo(this);
     iterator->RemoveCurrentFromGraph();
   } else {
     other->LinkTo(next());
   }
   set_previous(NULL);
   set_next(NULL);
 }
 
 
+// A misleadingly named function for use in template functions that replace
+// both definitions with definitions and branch comparisons with
+// comparisons.  In the branch case, leave the branch intact and replace its
+// comparison with another comparison.
+void BranchInstr::ReplaceWith(ComparisonInstr* other,
+                              ForwardInstructionIterator* ignored) {
+  // Record the new comparison's input uses.
+  for (intptr_t i = other->InputCount() - 1; i >= 0; --i) {
+    Value* input = other->InputAt(i);
+    input->definition()->AddInputUse(input);
+  }
+  SetComparison(other);
+}
+
+
+void BranchInstr::SetComparison(ComparisonInstr* comp) {
+  // The new comparison's input uses are already recorded in their
+  // definition's use lists.
+  for (intptr_t i = comp->InputCount() - 1; i >= 0; --i) {
+    Value* input = comp->InputAt(i);
+    input->set_instruction(this);
+    input->set_use_index(i);
+  }
+  // There should be no need to copy or unuse an environment.
+  ASSERT(comparison()->env() == NULL);
+  // Remove the current comparison's input uses.
+  comparison()->UnuseAllInputs();
+  ASSERT(!comp->HasUses());
+  comparison_ = comp;
+}
+
+
 // ==== Postorder graph traversal.
 static bool IsMarked(BlockEntryInstr* block,
                      GrowableArray<BlockEntryInstr*>* preorder) {
   // Detect that a block has been visited as part of the current
   // DiscoverBlocks (we can call DiscoverBlocks multiple times).  The block
   // will be 'marked' by (1) having a preorder number in the range of the
   // preorder array and (2) being in the preorder array at that index.
   intptr_t i = block->preorder_number();
   return (i >= 0) && (i < preorder->length()) && ((*preorder)[i] == block);
 }
@@ skipping 569 matching lines @@
           comp->InputAt(i)->definition()->representation()) {
         return this;
       }
     }
 
     // Replace the comparison if the replacement is used at this branch,
     // and has exactly one use.
     if ((comp->input_use_list()->instruction() == this) &&
         (comp->input_use_list()->next_use() == NULL) &&
         (comp->env_use_list() == NULL)) {
-      comparison()->UnuseAllInputs();
       comp->RemoveFromGraph();
       // It is safe to pass a NULL iterator because we're replacing the
       // comparison wrapped in a BranchInstr which does not modify the
       // linked list of instructions.
-      ReplaceWith(comp, NULL /* ignored */);
-      for (intptr_t i = 0; i < comp->InputCount(); ++i) {
-        Value* operand = comp->InputAt(i);
-        operand->set_instruction(this);
-      }
+      SetComparison(comp);
       if (FLAG_trace_optimization) {
         OS::Print("Merging comparison v%"Pd"\n", comp->ssa_temp_index());
       }
       // Clear the comparison's temp index and ssa temp index since the
       // value of the comparison is not used outside the branch anymore.
       ASSERT(comp->input_use_list() == NULL);
       comp->ClearSSATempIndex();
       comp->ClearTempIndex();
     }
   }
@@ skipping 1019 matching lines @@
     default:
       UNREACHABLE();
   }
   return kPowRuntimeEntry;
 }
 
 
 #undef __
 
 }  // namespace dart