[PATCH] D42691: [SimplifyCFG] Relax restriction for folding unconditional branches

[Serguei Katkov via Phabricator via llvm-commits]

skatkov added inline comments.


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Comment at: lib/Transforms/Utils/SimplifyCFG.cpp:5740
       Options.NeedCanonicalLoop &&
-      (LoopHeaders && (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
+      (LoopHeaders && std::distance(pred_begin(BB), pred_end(BB)) > 1 &&
+       (LoopHeaders->count(BB) || LoopHeaders->count(Succ)));
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efriedma wrote:
> getSinglePredecessor()?
make sense.


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Comment at: test/Transforms/SimplifyCFG/UncondBranchToHeader.ll:16
+  br label %header
+exit:
+  ret i32 %i
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efriedma wrote:
> Do we really need SimplifyCFG to rotate loops?  We have a dedicated LoopRotate pass for this sort of transform.
> 
> But I guess it's okay.
Hi Eli, I did not follow what you mean here as rotate loop?

Header will be the same. In this particular case the loop will just consists from one basic block header after transformation...


https://reviews.llvm.org/D42691