[turbofan] In effect control linearizer, only delay effect phi update for loops.

src/compiler/effect-control-linearizer.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/effect-control-linearizer.h"
 
 #include "src/code-factory.h"
 #include "src/compiler/access-builder.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/linkage.h"
@@ skipping 360 matching lines @@
                   .current_effect != effect) {
             effect = nullptr;
             break;
           }
         }
         if (effect == nullptr) {
           DCHECK_NE(IrOpcode::kIfException, control->opcode());
           // The input blocks do not have the same effect. We have
           // to create an effect phi node.
           inputs_buffer.clear();
-          inputs_buffer.resize(block->PredecessorCount(), graph()->start());
+          inputs_buffer.resize(block->PredecessorCount(), jsgraph()->Dead());

[Benedikt Meurer, 2016/07/16 12:35:29]

Nice!

           inputs_buffer.push_back(control);
           effect = graph()->NewNode(
               common()->EffectPhi(static_cast<int>(block->PredecessorCount())),
               static_cast<int>(inputs_buffer.size()), &(inputs_buffer.front()));
-          // Let us update the effect phi node later.
-          pending_effect_phis.push_back(PendingEffectPhi(effect, block));
+          // For loops, we update the effect phi node later to break cycles.
+          if (control->opcode() == IrOpcode::kLoop) {
+            pending_effect_phis.push_back(PendingEffectPhi(effect, block));
+          } else {
+            UpdateEffectPhi(effect, block, &block_effects);
+          }
         } else if (control->opcode() == IrOpcode::kIfException) {
           // The IfException is connected into the effect chain, so we need
           // to update the effect here.
           NodeProperties::ReplaceEffectInput(control, effect);
           effect = control;
         }
       }
     }
 
     // Fixup the Terminate node.
@@ skipping 1706 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoThrow);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8