2 files changed, 37 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
index 84bb6e4801c..97f48aac3bb 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
@@ -97,14 +97,11 @@ public:
     Values.push_back(std::move(Val));
   }
 
-  /// \brief Attempt to merge this DebugLocEntry with Next and return
-  /// true if the merge was successful. Entries can be merged if they
-  /// share the same Loc/Constant and if Next immediately follows this
-  /// Entry.
-  bool Merge(const DebugLocEntry &Next) {
-    // If this and Next are describing different pieces of the same
-    // variable, merge them by appending next's values to the current
-    // list of values.
+  /// \brief If this and Next are describing different pieces of the same
+  // variable, merge them by appending Next's values to the current
+  // list of values.
+  // Return true if the merge was successful.
+  bool MergeValues(const DebugLocEntry &Next) {
     if (Begin == Next.Begin && Values.size() > 0 && Next.Values.size() > 0) {
       DIVariable Var(Values[0].Variable);
       DIVariable NextVar(Next.Values[0].Variable);
@@ -115,6 +112,14 @@ public:
         return true;
       }
     }
+    return false;
+  }
+
+  /// \brief Attempt to merge this DebugLocEntry with Next and return
+  /// true if the merge was successful. Entries can be merged if they
+  /// share the same Loc/Constant and if Next immediately follows this
+  /// Entry.
+  bool MergeRanges(const DebugLocEntry &Next) {
     // If this and Next are describing the same variable, merge them.
     if ((End == Next.Begin && Values == Next.Values)) {
       End = Next.End;
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 7150a09cd4c..3dc03d9fb19 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1272,18 +1272,36 @@ DwarfDebug::buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
 
     auto Value = getDebugLocValue(Begin);
     DebugLocEntry Loc(StartLabel, EndLabel, Value);
-    if (DebugLoc.empty() || !DebugLoc.back().Merge(Loc)) {
-      // Add all values from still valid non-overlapping pieces.
+    bool couldMerge = false;
+
+    // If this is a piece, it may belong to the current DebugLocEntry.
+    if (DIVar.isVariablePiece()) {
+      // Add this value to the list of open ranges.
+      OpenRanges.push_back(std::make_pair(DIVar, Value));
+
+      // Attempt to add the piece to the last entry.
+      if (!DebugLoc.empty())
+        if (DebugLoc.back().MergeValues(Loc))
+          couldMerge = true;
+    }
+
+    if (!couldMerge) {
+      // Need to add a new DebugLocEntry. Add all values from still
+      // valid non-overlapping pieces.
       for (auto Range : OpenRanges)
         Loc.addValue(Range.second);
       DebugLoc.push_back(std::move(Loc));
     }
-    // Add this value to the list of open ranges.
-    if (DIVar.isVariablePiece())
-      OpenRanges.push_back(std::make_pair(DIVar, Value));
+
+    // Attempt to coalesce the ranges of two otherwise identical
+    // DebugLocEntries.
+    auto CurEntry = DebugLoc.rbegin();
+    auto PrevEntry = std::next(CurEntry);
+    if (PrevEntry != DebugLoc.rend() && PrevEntry->MergeRanges(*CurEntry))
+      DebugLoc.pop_back();
 
     DEBUG(dbgs() << "Values:\n";
-          for (auto Value : DebugLoc.back().getValues())
+          for (auto Value : CurEntry->getValues())
             Value.getVariable()->dump();
           dbgs() << "-----\n");
   }