[PATCH] D102615: [LoopDeletion] Break backedge if we can prove that the loop is exited on 1st iteration

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


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Comment at: llvm/lib/Transforms/Scalar/LoopDeletion.cpp:204
+  auto GetOnlyLivePred = [&](BasicBlock * BB)->BasicBlock * {
+    if (BB == Header)
+      return L->getLoopPredecessor();
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reames wrote:
> This check should probably be lifted to caller, and assert !Header here.  It confuses the interface of this lambda.
> 
> You could also consider renaming the lambda to getSolePredecessorOnFirstIteration.  
But why lifting it out? Semantically the sole predecessor of header on the 1st iteration is a loop pred. This allows us to process all loop blocks uniformly. Why do you think that header should be a special case outside this function?


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Comment at: llvm/lib/Transforms/Scalar/LoopDeletion.cpp:210
+        // 2 live preds.
+        if (OnlyPred)
+          return nullptr;
----------------
reames wrote:
> Note that predecessors can be listed multiple times due to switches.  You should check that OnlyPred is non-null and not equal to this block.
Good point, I'll add a test for this.


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  https://reviews.llvm.org/D102615/new/

https://reviews.llvm.org/D102615