[PATCH] D14122: [SimplifyCFG] Trim duplicate basic blocks in switch cases

[Dylan McKay via llvm-commits]

dylanmckay marked 2 inline comments as done.
dylanmckay added a comment.

Phillip's idea is a good one - it would be fairly easy to generalize this optimization so that it performes "prefix merging".

Do you think the new optimization should still live in `SimplifyCFG`? One problem with keeping it in `SimplifyCFG` is that block merging will interfere with tests even worse than with this patch (which is why the current patch adds a command line option to disable merging), causing them to wonder "where has my basic block gone?".

If the patch were to be split into a separate pass, it would be quite a small pass which would be overkill. Perhaps it would be better to keep the optimization in `SimplifyCFG` and keep the command line option for testing purposes.

Thoughts?


================
Comment at: lib/Transforms/Utils/SimplifyCFG.cpp:3461
@@ -3418,3 +3460,3 @@
   BasicBlock::iterator I = Succ->begin();
   while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
     int Idx = PHI->getBasicBlockIndex(BB);
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I understand this now - thanks for the explanation Sanjoy!


http://reviews.llvm.org/D14122