[DbgHistoryCalculator] Improve debug messages

I've found that a frequent source of debug information loss in optimized
code is due to DEBUG_VALUE intrinsics in a position of the instruction
stream that is outside the scope of the variable it describes.

Tracking these is pretty difficult with the existing debug messages of
the history calculator; this patch addresses the issue by making it
obvious when this event happens.

Differential Revision: https://reviews.llvm.org/D147718

diff --git a/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h b/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h
index 0cfe04a..7708df7 100644 (file)
--- a/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h
+++ b/llvm/include/llvm/CodeGen/DbgEntityHistoryCalculator.h
@@ -122,7 +122,7 @@ public:
   EntriesMap::const_iterator end() const { return VarEntries.end(); }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-  LLVM_DUMP_METHOD void dump() const;
+  LLVM_DUMP_METHOD void dump(StringRef FuncName) const;
 #endif
 };
 

diff --git a/llvm/lib/CodeGen/AsmPrinter/DbgEntityHistoryCalculator.cpp b/llvm/lib/CodeGen/AsmPrinter/DbgEntityHistoryCalculator.cpp
index 0b40cdb..55a0afc 100644 (file)
--- a/llvm/lib/CodeGen/AsmPrinter/DbgEntityHistoryCalculator.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DbgEntityHistoryCalculator.cpp
@@ -138,6 +138,9 @@ void DbgValueHistoryMap::trimLocationRanges(
   // references if any entries are removed.
   SmallVector<size_t, 4> Offsets;
 
+  LLVM_DEBUG(dbgs() << "Trimming location ranges for function '" << MF.getName()
+                    << "'\n");
+
   for (auto &Record : VarEntries) {
     auto &HistoryMapEntries = Record.second;
     if (HistoryMapEntries.empty())
@@ -213,6 +216,8 @@ void DbgValueHistoryMap::trimLocationRanges(
         // count of the closing entry, if one exists.
         if (EndIndex != NoEntry)
           ReferenceCount[EndIndex] -= 1;
+        LLVM_DEBUG(dbgs() << "Dropping value outside scope range of variable: ";
+                   StartMI->print(llvm::dbgs()););
       }
     }
 
@@ -253,6 +258,8 @@ void DbgValueHistoryMap::trimLocationRanges(
     // ToRemove indices are valid after each erase.
     for (EntryIndex Idx : llvm::reverse(ToRemove))
       HistoryMapEntries.erase(HistoryMapEntries.begin() + Idx);
+    LLVM_DEBUG(llvm::dbgs() << "New HistoryMap('" << LocalVar->getName()
+                            << "') size: " << HistoryMapEntries.size() << "\n");
   }
 }
 
@@ -555,8 +562,8 @@ void llvm::calculateDbgEntityHistory(const MachineFunction *MF,
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-LLVM_DUMP_METHOD void DbgValueHistoryMap::dump() const {
-  dbgs() << "DbgValueHistoryMap:\n";
+LLVM_DUMP_METHOD void DbgValueHistoryMap::dump(StringRef FuncName) const {
+  dbgs() << "DbgValueHistoryMap('" << FuncName << "'):\n";
   for (const auto &VarRangePair : *this) {
     const InlinedEntity &Var = VarRangePair.first;
     const Entries &Entries = VarRangePair.second;

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
index 858a3e7..1f1d243 100644 (file)
--- a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
@@ -273,7 +273,7 @@ void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
   InstOrdering.initialize(*MF);
   if (TrimVarLocs)
     DbgValues.trimLocationRanges(*MF, LScopes, InstOrdering);
-  LLVM_DEBUG(DbgValues.dump());
+  LLVM_DEBUG(DbgValues.dump(MF->getName()));
 
   // Request labels for the full history.
   for (const auto &I : DbgValues) {