[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

4 files changed, 31 insertions, 12 deletions

diff --git a/llvm/include/llvm/Support/LEB128.h b/llvm/include/llvm/Support/LEB128.h
index 6af6e9f3447..9feb0722922 100644
--- a/llvm/include/llvm/Support/LEB128.h
+++ b/llvm/include/llvm/Support/LEB128.h
@@ -19,9 +19,10 @@
 
 namespace llvm {
 
-/// Utility function to encode a SLEB128 value to an output stream.
-inline void encodeSLEB128(int64_t Value, raw_ostream &OS,
-                          unsigned PadTo = 0) {
+/// Utility function to encode a SLEB128 value to an output stream. Returns
+/// the length in bytes of the encoded value.
+inline unsigned encodeSLEB128(int64_t Value, raw_ostream &OS,
+                              unsigned PadTo = 0) {
   bool More;
   unsigned Count = 0;
   do {
@@ -42,7 +43,9 @@ inline void encodeSLEB128(int64_t Value, raw_ostream &OS,
     for (; Count < PadTo - 1; ++Count)
       OS << char(PadValue | 0x80);
     OS << char(PadValue);
+    Count++;
   }
+  return Count;
 }
 
 /// Utility function to encode a SLEB128 value to a buffer. Returns
@@ -73,9 +76,10 @@ inline unsigned encodeSLEB128(int64_t Value, uint8_t *p, unsigned PadTo = 0) {
   return (unsigned)(p - orig_p);
 }
 
-/// Utility function to encode a ULEB128 value to an output stream.
-inline void encodeULEB128(uint64_t Value, raw_ostream &OS,
-                          unsigned PadTo = 0) {
+/// Utility function to encode a ULEB128 value to an output stream. Returns
+/// the length in bytes of the encoded value.
+inline unsigned encodeULEB128(uint64_t Value, raw_ostream &OS,
+                              unsigned PadTo = 0) {
   unsigned Count = 0;
   do {
     uint8_t Byte = Value & 0x7f;
@@ -93,6 +97,7 @@ inline void encodeULEB128(uint64_t Value, raw_ostream &OS,
     OS << '\x00';
     Count++;
   }
+  return Count;
 }
 
 /// Utility function to encode a ULEB128 value to a buffer. Returns
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("");
+
+    }
   }
 };
 
diff --git a/llvm/test/CodeGen/ARM/debug-info-qreg.ll b/llvm/test/CodeGen/ARM/debug-info-qreg.ll
index 658e730bddd..44d30f871b1 100644
--- a/llvm/test/CodeGen/ARM/debug-info-qreg.ll
+++ b/llvm/test/CodeGen/ARM/debug-info-qreg.ll
@@ -4,10 +4,12 @@ target triple = "thumbv7-apple-macosx10.6.7"
 
 ;CHECK: sub-register DW_OP_regx
 ;CHECK-NEXT: 256
+;CHECK-NEXT: @
 ;CHECK-NEXT: DW_OP_piece
 ;CHECK-NEXT: 8
 ;CHECK-NEXT: sub-register DW_OP_regx
 ;CHECK-NEXT: 257
+;CHECK-NEXT: @
 ;CHECK-NEXT: DW_OP_piece
 ;CHECK-NEXT: 8
 
diff --git a/llvm/test/DebugInfo/X86/dw_op_minus.ll b/llvm/test/DebugInfo/X86/dw_op_minus.ll
index 30bf5837800..ffdf090c884 100644
--- a/llvm/test/DebugInfo/X86/dw_op_minus.ll
+++ b/llvm/test/DebugInfo/X86/dw_op_minus.ll
@@ -76,5 +76,5 @@ declare void @Capture(i32*)
 ; CHECK-NEXT: .byte	6                       # DW_OP_deref
 ; CHECK-NEXT: .byte	16                      # DW_OP_constu
 ; CHECK-NEXT: .byte	144                     # 400
-; CHECK-NEXT: .byte	3                       # DW_OP_minus
-; CHECK-NEXT: .byte	28
+; CHECK-NEXT: .byte	3                       #
+; CHECK-NEXT: .byte	28                      # DW_OP_minus