reland: [Local] Allow creating callbr with duplicate successors

Since D129288, callbr is allowed to have duplicate successors. This patch removes a limitation which prevents optimizations from actually producing such callbrs.

This is probably the riskiest of all the recent callbr changes, because code with incorrect assumptions might be lurking somewhere. I fixed the one case I encountered ahead of time in https://github.com/llvm/llvm-project/commit/8201e3ef5c84561260218bc041209611aac690e3.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D129997

Originally landed as
commit 08860f525a23 ("[Local] Allow creating callbr with duplicate successors")

Reverted in
commit 1cf6b93df168 ("Revert "[Local] Allow creating callbr with duplicate successors"")

1 files changed, 0 insertions, 12 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index c1735f7..1115b0b 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1090,18 +1090,6 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
     }
   }
 
-  // We cannot fold the block if it's a branch to an already present callbr
-  // successor because that creates duplicate successors.
-  for (BasicBlock *PredBB : predecessors(BB)) {
-    if (auto *CBI = dyn_cast<CallBrInst>(PredBB->getTerminator())) {
-      if (Succ == CBI->getDefaultDest())
-        return false;
-      for (unsigned i = 0, e = CBI->getNumIndirectDests(); i != e; ++i)
-        if (Succ == CBI->getIndirectDest(i))
-          return false;
-    }
-  }
-
   LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
 
   SmallVector<DominatorTree::UpdateType, 32> Updates;