[PATCH] D131827: [LoopSimplify][NFC] Replace depth-first order process as depth_first accessor.

[luxufan via Phabricator via llvm-commits]

StephenFan added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/LoopSimplify.cpp:731
   SmallVector<Loop *, 4> Worklist;
-  Worklist.push_back(L);
-
-  // Walk the worklist from front to back, pushing newly found sub loops onto
-  // the back. This will let us process loops from back to front in depth-first
-  // order. We can use this simple process because loops form a tree.
-  for (unsigned Idx = 0; Idx != Worklist.size(); ++Idx) {
-    Loop *L2 = Worklist[Idx];
-    Worklist.append(L2->begin(), L2->end());
-  }
+  for_each(depth_first(L),
+           [&Worklist](Loop *SubLoop) { Worklist.push_back(SubLoop); });
----------------
reames wrote:
> This looks wrong.  The original loop was pushing elements in inverse depth first order (i.e. from the root down) so that it could walk backwards through that order to get dfs.  You seem to be visiting each item in dfs, and adding them to worklist, and then still visiting them in inverse order.  
Thanks! Indeed, I was wrong. I found that the inverse_depth_first iterator accessor might be suitable.


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https://reviews.llvm.org/D131827