2 files changed, 43 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index 08aafda4bd8..665424805db 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -32,6 +32,7 @@
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/Function.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -753,6 +754,45 @@ bool BranchFolder::CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
   return true;
 }
 
+/// MergeCommonTailDebugLocs - Create merged DebugLocs of identical instructions
+/// across SameTails and assign it to the instruction in common tail.
+void BranchFolder::MergeCommonTailDebugLocs(unsigned commonTailIndex) {
+  MachineBasicBlock *MBB = SameTails[commonTailIndex].getBlock();
+
+  std::vector<MachineBasicBlock::iterator> NextCommonInsts(SameTails.size());
+  for (unsigned int i = 0 ; i != SameTails.size() ; ++i) {
+    if (i != commonTailIndex)
+      NextCommonInsts[i] = SameTails[i].getTailStartPos();
+    else {
+      assert(SameTails[i].getTailStartPos() == MBB->begin() &&
+          "MBB is not a common tail only block");
+    }
+  }
+
+  for (auto &MI : *MBB) {
+    if (MI.isDebugValue())
+      continue;
+    DebugLoc DL = MI.getDebugLoc();
+    for (unsigned int i = 0 ; i < NextCommonInsts.size() ; i++) {
+      if (i == commonTailIndex)
+        continue;
+
+      auto &Pos = NextCommonInsts[i];
+      assert(Pos != SameTails[i].getBlock()->end() &&
+          "Reached BB end within common tail");
+      while (Pos->isDebugValue()) {
+        ++Pos;
+        assert(Pos != SameTails[i].getBlock()->end() &&
+            "Reached BB end within common tail");
+      }
+      assert(MI.isIdenticalTo(*Pos) && "Expected matching MIIs!");
+      DL = DILocation::getMergedLocation(DL, Pos->getDebugLoc());
+      NextCommonInsts[i] = ++Pos;
+    }
+    MI.setDebugLoc(DL);
+  }
+}
+
 static void
 mergeOperations(MachineBasicBlock::iterator MBBIStartPos,
                 MachineBasicBlock &MBBCommon) {
@@ -905,10 +945,8 @@ bool BranchFolder::TryTailMergeBlocks(MachineBasicBlock *SuccBB,
     // Recompute common tail MBB's edge weights and block frequency.
     setCommonTailEdgeWeights(*MBB);
 
-    // Remove the original debug location from the common tail.
-    for (auto &MI : *MBB)
-      if (!MI.isDebugValue())
-        MI.setDebugLoc(DebugLoc());
+    // Merge debug locations across identical instructions for common tail
+    MergeCommonTailDebugLocs(commonTailIndex);
 
     // MBB is common tail.  Adjust all other BB's to jump to this one.
     // Traversal must be forwards so erases work.
diff --git a/llvm/lib/CodeGen/BranchFolding.h b/llvm/lib/CodeGen/BranchFolding.h
index 0773a2c86de..7c756e52bef 100644
--- a/llvm/lib/CodeGen/BranchFolding.h
+++ b/llvm/lib/CodeGen/BranchFolding.h
@@ -153,6 +153,7 @@ namespace llvm {
                                    MachineBasicBlock *SuccBB,
                                    unsigned maxCommonTailLength,
                                    unsigned &commonTailIndex);
+    void MergeCommonTailDebugLocs(unsigned commonTailIndex);
 
     bool OptimizeBranches(MachineFunction &MF);
     bool OptimizeBlock(MachineBasicBlock *MBB);