1 files changed, 26 insertions, 1 deletions
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index c9b0f208180..606bd8bacca 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -23,11 +23,13 @@
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/User.h"
@@ -142,8 +144,16 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
   }
 
   // Begin by getting rid of unneeded PHIs.
-  if (isa<PHINode>(BB->front()))
+  SmallVector<Value *, 4> IncomingValues;
+  if (isa<PHINode>(BB->front())) {
+    for (auto &I : *BB)
+      if (PHINode *PN = dyn_cast<PHINode>(&I)) {
+        if (PN->getIncomingValue(0) != PN)
+          IncomingValues.push_back(PN->getIncomingValue(0));
+      } else
+        break;
     FoldSingleEntryPHINodes(BB, MemDep);
+  }
 
   // Delete the unconditional branch from the predecessor...
   PredBB->getInstList().pop_back();
@@ -155,6 +165,21 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
   // Move all definitions in the successor to the predecessor...
   PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
 
+  // Eliminate duplicate dbg.values describing the entry PHI node post-splice.
+  for (auto *Incoming : IncomingValues) {
+    if (isa<Instruction>(Incoming)) {
+      SmallVector<DbgValueInst *, 2> DbgValues;
+      SmallDenseSet<std::pair<DILocalVariable *, DIExpression *>, 2>
+          DbgValueSet;
+      llvm::findDbgValues(DbgValues, Incoming);
+      for (auto &DVI : DbgValues) {
+        auto R = DbgValueSet.insert({DVI->getVariable(), DVI->getExpression()});
+        if (!R.second)
+          DVI->eraseFromParent();
+      }
+    }
+  }
+
   // Inherit predecessors name if it exists.
   if (!PredBB->hasName())
     PredBB->takeName(BB);