[PATCH] [DWARF] Fix a few corner cases in expression emission

[Adrian Prantl]

Thanks for looking into this! I have a few questions inline.


REPOSITORY
  rL LLVM

================
Comment at: lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1565
@@ -1564,1 +1564,3 @@
     for (const auto &Entry : DebugLocs.getEntries(List)) {
+       if (Entry.BeginSym == Entry.EndSym)
+        continue;
----------------
Hopefully this can become an assertion with Duncan's pending patch.

================
Comment at: lib/CodeGen/AsmPrinter/DwarfExpression.cpp:219
@@ -214,3 +218,3 @@
   case dwarf::DW_OP_plus: {
     // [DW_OP_reg,Offset,DW_OP_plus,DW_OP_deref] --> [DW_OP_breg,Offset].
     auto N = I.getNext();
----------------
This comment now needs to be moved down to the "if (DW_OP_deref)" block.

================
Comment at: lib/CodeGen/AsmPrinter/DwarfExpression.cpp:237
@@ +236,3 @@
+      } else {
+        ValidReg = AddMachineRegIndirect(MachineReg, Offset);
+        IsOnStack = true;
----------------
The indirection here seems wrong:
To reach this clause, we need an expression like "DW_OP_reg Offset DW_OP_plus (DW_OP_bit_Piece x y)?"
Shouldn't this be just an unconditional AddMachineRegPiece()?

http://reviews.llvm.org/D10302

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