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, 21 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
index 3beb799203b..8cfe39d2ca3 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugLocEntry.h
@@ -10,6 +10,7 @@
 #ifndef CODEGEN_ASMPRINTER_DEBUGLOCENTRY_H__
 #define CODEGEN_ASMPRINTER_DEBUGLOCENTRY_H__
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/MC/MachineLocation.h"
 #include "llvm/MC/MCSymbol.h"
 
@@ -106,17 +107,36 @@ public:
   /// 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.
+    if (Begin == Next.Begin && Values.size() > 0 && Next.Values.size() > 0) {
+      DIVariable Var(Values[0].Variable);
+      DIVariable NextVar(Next.Values[0].Variable);
+      if (Var.getName() == NextVar.getName() &&
+          Var.isVariablePiece() && NextVar.isVariablePiece()) {
+        Values.append(Next.Values.begin(), Next.Values.end());
+        End = Next.End;
+        return true;
+      }
+    }
+    // If this and Next are describing the same variable, merge them.
     if ((End == Next.Begin && Values == Next.Values)) {
       End = Next.End;
       return true;
     }
     return false;
   }
+
   const MCSymbol *getBeginSym() const { return Begin; }
   const MCSymbol *getEndSym() const { return End; }
   const DwarfCompileUnit *getCU() const { return Unit; }
   const ArrayRef<Value> getValues() const { return Values; }
-  void addValue(Value Val) { Values.push_back(Val); }
+  void addValue(Value Val) {
+    assert(DIVariable(Val.Variable).isVariablePiece() &&
+           "multi-value DebugLocEntries must be pieces");
+    Values.push_back(Val);
+  }
 };
 
 }