[DebugInfo] Align comments in debug_loc section

Summary:
This commit updates the BufferByteStreamer, used by DebugLocStream
to buffer bytes/comments to put in the debug_loc section, to
make sure that the Buffer and Comments vectors are synced.
Previously, when an SLEB128 or ULEB128 was emitted together with
a comment, the vectors could be out-of-sync if the LEB encoding
added several entries to the Buffer vectors, while we only added
a single entry to the Comments vector.

The goal with this is to get the comments in the debug_loc
section in the .s file correctly aligned.

Example (using ARM as target):
Instead of

  .byte 144                     @ sub-register DW_OP_regx
  .byte 128                     @ 256
  .byte 2                       @ DW_OP_piece
  .byte 147                     @ 8
  .byte 8                       @ sub-register DW_OP_regx
  .byte 144                     @ 257
  .byte 129                     @ DW_OP_piece
  .byte 2                       @ 8
  .byte 147                     @
  .byte 8                       @

we now get

  .byte 144                     @ sub-register DW_OP_regx
  .byte 128                     @ 256
  .byte 2                       @
  .byte 147                     @ DW_OP_piece
  .byte 8                       @ 8
  .byte 144                     @ sub-register DW_OP_regx
  .byte 129                     @ 257
  .byte 2                       @
  .byte 147                     @ DW_OP_piece
  .byte 8                       @ 8

Reviewers: JDevlieghere, rnk, aprantl

Reviewed By: aprantl

Subscribers: davide, Ka-Ka, uabelho, aemerson, javed.absar, kristof.beyls, llvm-commits, JDevlieghere

Differential Revision: https://reviews.llvm.org/D41763

llvm-svn: 321907

1 files changed, 16 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h b/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h
index aaf6180c940..34ad66f8a39 100644
--- a/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h
+++ b/llvm/lib/CodeGen/AsmPrinter/ByteStreamer.h
@@ -93,15 +93,27 @@ public:
   }
   void EmitSLEB128(uint64_t DWord, const Twine &Comment) override {
     raw_svector_ostream OSE(Buffer);
-    encodeSLEB128(DWord, OSE);
-    if (GenerateComments)
+    unsigned Length = encodeSLEB128(DWord, OSE);
+    if (GenerateComments) {
       Comments.push_back(Comment.str());
+      // Add some empty comments to keep the Buffer and Comments vectors aligned
+      // with each other.
+      for (size_t i = 1; i < Length; ++i)
+        Comments.push_back("");
+
+    }
   }
   void EmitULEB128(uint64_t DWord, const Twine &Comment) override {
     raw_svector_ostream OSE(Buffer);
-    encodeULEB128(DWord, OSE);
-    if (GenerateComments)
+    unsigned Length = encodeULEB128(DWord, OSE);
+    if (GenerateComments) {
       Comments.push_back(Comment.str());
+      // Add some empty comments to keep the Buffer and Comments vectors aligned
+      // with each other.
+      for (size_t i = 1; i < Length; ++i)
+        Comments.push_back("");
+
+    }
   }
 };