[simplifycfg][loop-simplify] Preserve loop metadata in 2 transformations.

insertUniqueBackedgeBlock in lib/Transforms/Utils/LoopSimplify.cpp now
propagates existing llvm.loop metadata to newly the added backedge.

llvm::TryToSimplifyUncondBranchFromEmptyBlock in lib/Transforms/Utils/Local.cpp
now propagates existing llvm.loop metadata to the branch instructions in the
predecessor blocks of the empty block that is removed.

Differential Revision: https://reviews.llvm.org/D26495

llvm-svn: 287341

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index 89933e0f574..d24c1c41557 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -470,13 +470,21 @@ static BasicBlock *insertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader,
   }
 
   // Now that all of the PHI nodes have been inserted and adjusted, modify the
-  // backedge blocks to just to the BEBlock instead of the header.
+  // backedge blocks to jump to the BEBlock instead of the header.
+  // If one of the backedges has llvm.loop metadata attached, we remove
+  // it from the backedge and add it to BEBlock.
+  unsigned LoopMDKind = BEBlock->getContext().getMDKindID("llvm.loop");
+  MDNode *LoopMD = nullptr;
   for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
     TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
+    if (!LoopMD)
+      LoopMD = TI->getMetadata(LoopMDKind);
+    TI->setMetadata(LoopMDKind, nullptr);
     for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
       if (TI->getSuccessor(Op) == Header)
         TI->setSuccessor(Op, BEBlock);
   }
+  BEBlock->getTerminator()->setMetadata(LoopMDKind, LoopMD);
 
   //===--- Update all analyses which we must preserve now -----------------===//