Be more careful about exiting inlined functions in a test context.

When falling off the end of a function inlined in a test context, we cannot
constant fold the test of undefined away. The graph builder assumes that
control flow always reaches both branches of a test.

Instead, explicitly test and branch on "undefined". Introduce a pair of
empty blocks to hold the necessary LeaveInlined instructions.

Review URL: http://codereview.chromium.org/5566005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5927 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -3977,17 +3977,27 @@ bool HGraphBuilder::TryInline(Call* expr) {
   if (body->HasExit()) {
     // Add a return of undefined if control can fall off the body.  In a
     // test context, undefined is false.
-    HValue* return_value = NULL;
-    HBasicBlock* target = NULL;
+    HValue* return_value = graph()->GetConstantUndefined();
     if (test_context == NULL) {
       ASSERT(function_return_ != NULL);
-      return_value = graph()->GetConstantUndefined();
-      target = function_return_;
+      body->exit_block()->AddLeaveInlined(return_value, function_return_);
     } else {
-      return_value = graph()->GetConstantFalse();
-      target = test_context->if_false();
+      // The graph builder assumes control can reach both branches of a
+      // test, so we materialize the undefined value and test it rather than
+      // simply jumping to the false target.
+      //
+      // TODO(3168478): refactor to avoid this.
+      HBasicBlock* materialize_true = graph()->CreateBasicBlock();
+      HBasicBlock* materialize_false = graph()->CreateBasicBlock();
+      HBranch* branch =
+          new HBranch(materialize_true, materialize_false, return_value);
+      body->exit_block()->Finish(branch);
+
+      materialize_true->AddLeaveInlined(graph()->GetConstantTrue(),
+                                        test_context->if_true());
+      materialize_false->AddLeaveInlined(graph()->GetConstantFalse(),
+                                         test_context->if_false());
     }
-    body->exit_block()->AddLeaveInlined(return_value, target);
     body->set_exit_block(NULL);
   }
 

test/mjsunit/compiler/regress-3260426.js

+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Falling off the end of a function returns the undefined value
+// (false in a test context).  This should happen even when inlined
+// (e.g., if --always-opt) and when it is the only exit from the
+// function.
+function always_false() {}
+function test() { return always_false() ? 0 : 1; }
+
+assertEquals(1, test());
+