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

src/compiler/register-allocator.cc

 // Copyright 2014 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/base/adapters.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/register-allocator.h"
 #include "src/string-stream.h"
 
 namespace v8 {
@@ skipping 2424 matching lines @@
   const InstructionBlock* end_block = GetInstructionBlock(code(), end);
 
   if (end_block == start_block) {
     // The interval is split in the same basic block. Split at the latest
     // possible position.
     return end;
   }
 
   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 ||
+        loop->rpo_number().ToInt() <= start_block->rpo_number().ToInt()) {
+      // No more loops or loop starts before the lifetime start.
+      break;
+    }
+    block = loop;
+  } while (true);
 
   // We did not find any suitable outer loop. Split at the latest possible
   // position unless end_block is a loop header itself.
   if (block == end_block && !end_block->IsLoopHeader()) return end;
 
   return LifetimePosition::GapFromInstructionIndex(
       block->first_instruction_index());
 }
 
 
@@ skipping 1114 matching lines @@
                            spill_operand);
       }
     }
   }
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8