Fixed issue 4580 introduced by revision 10894.

runtime/vm/flow_graph.cc

 // Copyright (c) 2012, 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.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/intermediate_language.h"
 #include "vm/longjump.h"
@@ skipping 253 matching lines @@
 
   // Initialize start environment.
   GrowableArray<Definition*> start_env(variable_count());
   for (intptr_t i = 0; i < parameter_count(); ++i) {
     ParameterInstr* param = new ParameterInstr(i);
     param->set_ssa_temp_index(alloc_ssa_temp_index());  // New SSA temp.
     start_env.Add(param);
   }
 
   // All locals are initialized with #null.
-  Definition* null_def = new BindInstr(BindInstr::kUsed,
-                                       new ConstantVal(Object::ZoneHandle()));
-  null_def->set_ssa_temp_index(alloc_ssa_temp_index());  // New SSA temp.
+  Definition* null_defn = new BindInstr(BindInstr::kUsed,
+                                        new ConstantVal(Object::ZoneHandle()));
+  // The null definition should not appear in input positions.
+  ASSERT(null_defn->ssa_temp_index() == -1);
   while (start_env.length() < variable_count()) {
-    start_env.Add(null_def);
+    start_env.Add(null_defn);
   }
   graph_entry_->set_start_env(
       new Environment(start_env, non_copied_parameter_count_));
 
   BlockEntryInstr* normal_entry = graph_entry_->SuccessorAt(0);
   ASSERT(normal_entry != NULL);  // Must have entry.
   GrowableArray<Definition*> env(variable_count());
   env.AddArray(start_env);
   RenameRecursive(normal_entry, &env, live_phis);
 }
 
 
+// Helper to either use the constant value of a defintion or the defintion.

[srdjan, 2012/08/20 16:54:20]

s/defintion/definition/ (twice)

+static Value* UseDefinition(Definition* defn) {
+  if (defn->IsBind() && defn->AsBind()->computation()->IsConstant()) {
+    return defn->AsBind()->computation()->AsConstant();
+  } else {
+    return new UseVal(defn);
+  }
+}
+
+
 void FlowGraph::RenameRecursive(BlockEntryInstr* block_entry,
                                 GrowableArray<Definition*>* env,
                                 GrowableArray<PhiInstr*>* live_phis) {
   // 1. Process phis first.
   if (block_entry->IsJoinEntry()) {
     JoinEntryInstr* join = block_entry->AsJoinEntry();
     if (join->phis() != NULL) {
       for (intptr_t i = 0; i < join->phis()->length(); ++i) {
         PhiInstr* phi = (*join->phis())[i];
         if (phi != NULL) {
@@ skipping 28 matching lines @@
       BindInstr* as_bind = v->AsUse()->definition()->AsBind();
       if ((as_bind != NULL) &&
           (as_bind->computation()->IsLoadLocal() ||
            as_bind->computation()->IsStoreLocal())) {
         // Assert exactly one use.
         ASSERT(as_bind->use_list() == v);
         ASSERT(as_bind->use_list()->next_use() == NULL);
         // Remove the use, its definition and copy the environment value.
         v->RemoveFromUseList();
         as_bind->RemoveFromGraph();
+        // Assert we are not referencing nulls in the initial environment.
+        ASSERT(input_defn->ssa_temp_index() != -1);
         current->SetInputAt(i, new UseVal(input_defn));
       }
     }
 
     // Drop pushed arguments for calls.
     for (intptr_t j = 0; j < current->ArgumentCount(); j++) {
       env->RemoveLast();
     }
 
     // 2b. Handle LoadLocal and StoreLocal.
@@ skipping 63 matching lines @@
       block_entry->last_instruction()->SuccessorAt(0)->IsJoinEntry()) {
     JoinEntryInstr* successor =
         block_entry->last_instruction()->SuccessorAt(0)->AsJoinEntry();
     intptr_t pred_index = successor->IndexOfPredecessor(block_entry);
     ASSERT(pred_index >= 0);
     if (successor->phis() != NULL) {
       for (intptr_t i = 0; i < successor->phis()->length(); ++i) {
         PhiInstr* phi = (*successor->phis())[i];
         if (phi != NULL) {
           // Rename input operand.
-          phi->SetInputAt(pred_index, new UseVal((*env)[i]));
+          phi->SetInputAt(pred_index, UseDefinition((*env)[i]));
         }
       }
     }
   }
 }
 
 
 void FlowGraph::MarkLivePhis(GrowableArray<PhiInstr*>* live_phis) {
   while (!live_phis->is_empty()) {
     PhiInstr* phi = live_phis->Last();
@@ skipping 17 matching lines @@
   intptr_t len = OS::SNPrint(NULL, 0, kFormat, function_name, reason) + 1;
   char* chars = Isolate::Current()->current_zone()->Alloc<char>(len);
   OS::SNPrint(chars, len, kFormat, function_name, reason);
   const Error& error = Error::Handle(
       LanguageError::New(String::Handle(String::New(chars))));
   Isolate::Current()->long_jump_base()->Jump(1, error);
 }
 
 
 }  // namespace dart