[turbofan] Fix small redundancy in register allocator per TODO.

src/compiler/register-allocator.cc

Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc b/src/compiler/register-allocator.cc
index 0465139bba3fdedd614d5b4a06d2be2fcc4999c6..575fc1f7cd82fc489eee9c2009a4544d6df3ea4c 100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -2442,12 +2442,12 @@ LifetimePosition RegisterAllocator::FindOptimalSplitPos(LifetimePosition start,
 
   const InstructionBlock* block = end_block;
   // Find header of outermost loop.
-  // TODO(titzer): fix redundancy below.
-  while (GetContainingLoop(code(), block) != nullptr &&
-         GetContainingLoop(code(), block)->rpo_number().ToInt() >
-             start_block->rpo_number().ToInt()) {
-    block = GetContainingLoop(code(), block);
-  }
+  do {
+    const InstructionBlock* loop = GetContainingLoop(code(), block);
+    if (loop == nullptr) break;
+    if (loop->rpo_number().ToInt() <= start_block->rpo_number().ToInt()) break;

[Mircea Trofin, 2016/02/12 17:43:58]

Nit: just one if? if (loop == nullptr || loop->rpo_number.... ) { break; }

...see below nit, too.

+    block = loop;
+  } while (true);

[Mircea Trofin, 2016/02/12 17:43:59]

Nit: personal preference, I'd rather see the exit condition here, rather than
while (true).

 
   // We did not find any suitable outer loop. Split at the latest possible
   // position unless end_block is a loop header itself.