Fix issue 982.

When splitting at the beginning of a use interval assign coinciding position to the split child instead of leaving it to parent.

BUG=v8:982

Review URL: http://codereview.chromium.org/5898001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6031 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/lithium-allocator.cc

@@ -296,13 +296,21 @@ void LiveRange::SplitAt(LifetimePosition position, LiveRange* result) {
   // position is contained in one of the intervals in the chain, we
   // split that interval and use the first part.
   UseInterval* current = FirstSearchIntervalForPosition(position);
+
+  // If the split position coincides with the beginning of a use interval
+  // we need to split use positons in a special way.
+  bool split_at_start = false;
+
   while (current != NULL) {
     if (current->Contains(position)) {
       current->SplitAt(position);
       break;
     }
     UseInterval* next = current->next();
-    if (next->start().Value() >= position.Value()) break;
+    if (next->start().Value() >= position.Value()) {
+      split_at_start = (next->start().Value() == position.Value());
+      break;
+    }
     current = next;
   }
 
@@ -319,10 +327,20 @@ void LiveRange::SplitAt(LifetimePosition position, LiveRange* result) {
   // position after it.
   UsePosition* use_after = first_pos_;
   UsePosition* use_before = NULL;
+  if (split_at_start) {
+    // The split position coincides with the beginning of a use interval (the
+    // end of a lifetime hole). Use at this position should be attributed to
+    // the split child because split child owns use interval covering it.
+    while (use_after != NULL && use_after->pos().Value() < position.Value()) {
+      use_before = use_after;
+      use_after = use_after->next();
+    }
+  } else {
     while (use_after != NULL && use_after->pos().Value() <= position.Value()) {
       use_before = use_after;
       use_after = use_after->next();
     }
+  }
 
   // Partition original use positions to the two live ranges.
   if (use_before != NULL) {

test/mjsunit/regress/regress-982.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.
+
+function f(a) {
+ return {className: 'xxx'};
+};
+
+var x = 1;
+
+function g(active) {
+ for (i = 1; i <= 20000; i++) {
+   if (i == active) {
+     x = i;
+     if (f("" + i) != null) { }
+   } else {
+     if (f("" + i) != null) { }
+   }
+ }
+}
+
+g(0);