[turbofan] Fix exit control flow in TryCatchBuilder.

This makes sure that the exit control flow that merges the try-block
with the catch-block after a try-catch-statement creates a new merge
node in cases where it has to. Otherwise dangling phi nodes might have
the wrong number of value inputs.

R=bmeurer@chromium.org
TEST=mjsunit/regress/regress-crbug-505354
BUG=chromium:505354
LOG=N

Review URL: https://codereview.chromium.org/1213183003

Cr-Commit-Position: refs/heads/master@{#29362}

src/compiler/control-builders.cc

@@ -160,6 +160,7 @@ void BlockBuilder::EndBlock() {
 
 
 void TryCatchBuilder::BeginTry() {
+  exit_environment_ = environment()->CopyAsUnreachable();
   catch_environment_ = environment()->CopyAsUnreachable();
   catch_environment_->Push(the_hole());
 }
@@ -174,7 +175,7 @@ void TryCatchBuilder::Throw(Node* exception) {
 
 
 void TryCatchBuilder::EndTry() {
-  exit_environment_ = environment();
+  exit_environment_->Merge(environment());
   exception_node_ = catch_environment_->Pop();
   set_environment(catch_environment_);
 }

test/mjsunit/regress/regress-crbug-505354.js

+// 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.
+
+// Flags: --allow-natives-syntax --turbo-filter=f
+
+function f() {
+  "use strict";
+  try {
+    for (let i = 0; i < 10; i++) {}
+  } catch(e) {}
+}
+%OptimizeFunctionOnNextCall(f);
+f();