From e09ee3faaf3d74af842133b8e00a9ea3ff0edff7 Mon Sep 17 00:00:00 2001
From: Adrian Prantl <aprantl@apple.com>
Date: Mon, 11 Aug 2014 20:59:28 +0000
Subject: [PATCH] Debug info: Refactor DebugLocEntry's Merge function to make
 buildLocationLists easier to read.

The previous implementation conflated the merging of individual pieces
and the merging of entire DebugLocEntries.

By splitting this functionality into two separate functions the intention
of the code should be clearer.

llvm-svn: 215383
---
 llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h | 21 +++++++++------
 llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp  | 30 ++++++++++++++++-----
 2 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
index 84bb6e4801c3..97f48aac3bb4 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 7150a09cd4ca..3dc03d9fb196 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");
   }