Debug info: Infrastructure to support debug locations for fragmented

variables (for example, by-value struct arguments passed in registers, or
large integer values split across several smaller registers).
On the IR level, this adds a new type of complex address operation OpPiece
to DIVariable that describes size and offset of a variable fragment.
On the DWARF emitter level, all pieces describing the same variable are
collected, sorted and emitted as DWARF expressions using the DW_OP_piece
and DW_OP_bit_piece operators.

http://reviews.llvm.org/D3373
rdar://problem/15928306

What this patch doesn't do / Future work:
- This patch only adds the backend machinery to make this work, patches
  that change SROA and SelectionDAG's type legalizer to actually create
  such debug info will follow. (http://reviews.llvm.org/D2680)
- Making the DIVariable complex expressions into an argument of dbg.value
  will reduce the memory footprint of the debug metadata.
- The sorting/uniquing of pieces should be moved into DebugLocEntry,
  to facilitate the merging of multi-piece entries.

llvm-svn: 214576

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
index f45314ae0f1..fd6c155388c 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -535,6 +535,12 @@ class DwarfDebug : public AsmPrinterHandler {
   /// \brief Populate LexicalScope entries with variables' info.
   void collectVariableInfo(SmallPtrSet<const MDNode *, 16> &ProcessedVars);
 
+  /// \brief Build the location list for all DBG_VALUEs in the
+  /// function that describe the same variable.
+  void buildLocationList(SmallVectorImpl<DebugLocEntry> &DebugLoc,
+                         const DbgValueHistoryMap::InstrRanges &Ranges,
+                         DwarfCompileUnit *TheCU);
+
   /// \brief Collect variable information from the side table maintained
   /// by MMI.
   void collectVariableInfoFromMMITable(SmallPtrSet<const MDNode *, 16> &P);
@@ -642,6 +648,13 @@ public:
   /// \brief Emit an entry for the debug loc section. This can be used to
   /// handle an entry that's going to be emitted into the debug loc section.
   void emitDebugLocEntry(ByteStreamer &Streamer, const DebugLocEntry &Entry);
+  /// \brief emit a single value for the debug loc section.
+  void emitDebugLocValue(ByteStreamer &Streamer,
+                         const DebugLocEntry::Value &Value);
+  /// Emits an optimal (=sorted) sequence of DW_OP_pieces.
+  void emitLocPieces(ByteStreamer &Streamer,
+                     const DITypeIdentifierMap &Map,
+                     ArrayRef<DebugLocEntry::Value> Values);
 
   /// Emit the location for a debug loc entry, including the size header.
   void emitDebugLocEntryLocation(const DebugLocEntry &Entry);