PGO: preserve branch-weight metadata when simplifying Switch

Hanlde the case when we split the default edge if the default target has "icmp"
and unconditinal branch.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164076 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 67cb8f59ba..1316b859e8 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2425,6 +2425,21 @@ static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
   // the switch to the merge point on the compared value.
   BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
                                          BB->getParent(), BB);
+  SmallVector<uint64_t, 8> Weights;
+  bool HasWeights = HasBranchWeights(SI);
+  if (HasWeights) {
+    GetBranchWeights(SI, Weights);
+    if (Weights.size() == 1 + SI->getNumCases()) {
+      // Split weight for default case to case for "Cst".
+      Weights[0] = (Weights[0]+1) >> 1;
+      Weights.push_back(Weights[0]);
+
+      SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
+      SI->setMetadata(LLVMContext::MD_prof,
+                      MDBuilder(SI->getContext()).
+                      createBranchWeights(MDWeights));
+    }
+  }
   SI->addCase(Cst, NewBB);
 
   // NewBB branches to the phi block, add the uncond branch and the phi entry.