[turbofan] Split before loops.

src/compiler/greedy-allocator.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/greedy-allocator.h"
 #include "src/compiler/register-allocator.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 458 matching lines @@
   UsePosition* next_use = range->NextRegisterPosition(after_call);
   if (!next_use) return LifetimePosition::Invalid();
 
   LifetimePosition split_pos = FindOptimalSplitPos(after_call, next_use->pos());
   split_pos =
       GetSplitPositionForInstruction(range, split_pos.ToInstructionIndex());
   return split_pos;
 }
 
 
+LifetimePosition GreedyAllocator::FindSplitPositionBeforeLoops(
+    LiveRange* range) {
+  LifetimePosition end = range->End();
+  if (end.ToInstructionIndex() >= code()->LastInstructionIndex()) {
+    end =
+        LifetimePosition::GapFromInstructionIndex(end.ToInstructionIndex() - 1);
+  }
+  LifetimePosition pos = FindOptimalSplitPos(range->Start(), end);
+  pos = GetSplitPositionForInstruction(range, pos.ToInstructionIndex());
+  return pos;
+}
+
+
 void GreedyAllocator::SplitOrSpillBlockedRange(LiveRange* range) {
   if (TrySplitAroundCalls(range)) return;
-  auto pos = GetLastResortSplitPosition(range, code());
+
+  LifetimePosition pos = FindSplitPositionBeforeLoops(range);
+
+  if (!pos.IsValid()) pos = GetLastResortSplitPosition(range, code());
   if (pos.IsValid()) {
     LiveRange* tail = Split(range, data(), pos);
     DCHECK(tail != range);
     scheduler().Schedule(tail);
     scheduler().Schedule(range);
     return;
   }
   SpillRangeAsLastResort(range);
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8