[Debug-Info] Add names for the debug line prologue.

[Esme]

Summary

This is a minor patch to add names for the debug line prologue, as a follow-up of D95998.

[dblaikie]

Looks good

[shchenz]

Thanks for doing this. LGTM too.

[ikudrin]

LGTM, thanks!

llvm/lib/MC/MCDwarf.cpp

478–481

These two symbols make a pair, wouldn't it be better to put them under a common comment?

llvm/lib/MC/MCDwarf.cpp

MCDwarfLineTableHeader::Emit(MCStreamer *MCOS, MCDwarfLineTableParams Params,
   unsigned LineTableVersion = context.getDwarfVersion();
   MCOS->emitInt16(LineTableVersion);
 
   // In v5, we get address info next.
   if (LineTableVersion >= 5) {
     MCOS->emitInt8(context.getAsmInfo()->getCodePointerSize());
     MCOS->emitInt8(0); // Segment selector; same as EmitGenDwarfAranges.
   }
 
-  MCSymbol *ProStartSym = context.createTempSymbol();
-
-  // Create a symbol for the end of the prologue (to be set when we get there).
-  MCSymbol *ProEndSym = context.createTempSymbol(); // Lprologue_end
+  // Create symbols for the start/end of the prologue.
+  MCSymbol *ProStartSym = context.createTempSymbol("prologue_start");
+  MCSymbol *ProEndSym = context.createTempSymbol("prologue_end");
 
   // Length of the prologue, is the next 4 bytes (8 bytes for DWARF64). This is
   // actually the length from after the length word, to the end of the prologue.
   MCOS->emitAbsoluteSymbolDiff(ProEndSym, ProStartSym, OffsetSize);
 
   MCOS->emitLabel(ProStartSym);
 
   // Parameters of the state machine, are next.

llvm/test/DebugInfo/XCOFF/empty.ll

 ; ASM32-NEXT:  L..info_string4:
 ; ASM32-NEXT:          .byte   'i,'n,'t,0000                   # string offset=36
 ; ASM32-NEXT:          .toc
 ; ASM32:               .dwsect 0x20000
 ; ASM32-NEXT:  L...dwline:
 ; ASM32-NEXT:  L..debug_line_0:
 ; ASM32-NEXT:  .set L..line_table_start0, L..debug_line_0-4
 ; ASM32-NEXT:          .vbyte  2, 4
-; ASM32-NEXT:          .vbyte  4, L..tmp5-L..tmp4
-; ASM32-NEXT:  L..tmp4:
+; ASM32-NEXT:          .vbyte 4, L..prologue_end0-L..prologue_start0
+; ASM32-NEXT:  L..prologue_start0:
 ; ASM32-NEXT:          .byte   4
 ; ASM32-NEXT:          .byte   1
 ; ASM32-NEXT:          .byte   1
 ; ASM32-NEXT:          .byte   -5
 ; ASM32-NEXT:          .byte   14
 ; ASM32-NEXT:          .byte   13
 ; ASM32-NEXT:          .byte   0
 ; ASM32-NEXT:          .byte   1

 ; ASM32-NEXT:          .byte   0
 ; ASM32-NEXT:          .byte   0
 ; ASM32-NEXT:          .byte   '1,'.,'c
 ; ASM32-NEXT:          .byte   0
 ; ASM32-NEXT:          .byte   1
 ; ASM32-NEXT:          .byte   0
 ; ASM32-NEXT:          .byte   0
 ; ASM32-NEXT:          .byte   0
-; ASM32-NEXT:  L..tmp5:
+; ASM32-NEXT:  L..prologue_end0:
 ; ASM32-NEXT:          .byte   0                               # Set address to L..tmp0
 ; ASM32-NEXT:          .byte   5
 ; ASM32-NEXT:          .byte   2
 ; ASM32-NEXT:          .vbyte  4, L..tmp0
 ; ASM32-NEXT:          .byte   19                              # Start sequence
 ; ASM32-NEXT:          .byte   5
 ; ASM32-NEXT:          .byte   3
 ; ASM32-NEXT:          .byte   10

 ; ASM64-NEXT:  L..info_string4:
 ; ASM64-NEXT:          .byte   'i,'n,'t,0000                   # string offset=36
 ; ASM64-NEXT:          .toc
 ; ASM64:               .dwsect 0x20000
 ; ASM64-NEXT:  L...dwline:
 ; ASM64-NEXT:  L..debug_line_0:
 ; ASM64-NEXT:  .set L..line_table_start0, L..debug_line_0-12
 ; ASM64-NEXT:          .vbyte  2, 4
-; ASM64-NEXT:          .vbyte  8, L..tmp5-L..tmp4
-; ASM64-NEXT:  L..tmp4:
+; ASM64-NEXT:          .vbyte  8, L..prologue_end0-L..prologue_start0
+; ASM64-NEXT:  L..prologue_start0:
 ; ASM64-NEXT:          .byte   4
 ; ASM64-NEXT:          .byte   1
 ; ASM64-NEXT:          .byte   1
 ; ASM64-NEXT:          .byte   -5
 ; ASM64-NEXT:          .byte   14
 ; ASM64-NEXT:          .byte   13
 ; ASM64-NEXT:          .byte   0
 ; ASM64-NEXT:          .byte   1

 ; ASM64-NEXT:          .byte   0
 ; ASM64-NEXT:          .byte   0
 ; ASM64-NEXT:          .byte   '1,'.,'c
 ; ASM64-NEXT:          .byte   0
 ; ASM64-NEXT:          .byte   1
 ; ASM64-NEXT:          .byte   0
 ; ASM64-NEXT:          .byte   0
 ; ASM64-NEXT:          .byte   0
-; ASM64-NEXT:  L..tmp5:
+; ASM64-NEXT:  L..prologue_end0:
 ; ASM64-NEXT:          .byte   0                               # Set address to L..tmp0
 ; ASM64-NEXT:          .byte   9
 ; ASM64-NEXT:          .byte   2
 ; ASM64-NEXT:          .vbyte  8, L..tmp0
 ; ASM64-NEXT:          .byte   19                              # Start sequence
 ; ASM64-NEXT:          .byte   5
 ; ASM64-NEXT:          .byte   3
 ; ASM64-NEXT:          .byte   10

llvm/test/DebugInfo/XCOFF/explicit-section.ll

 ; CHECK-NEXT:  L..info_string5:
 ; CHECK-NEXT:          .byte   'm,'a,'i,'n,0000                # string offset=39
 ; CHECK-NEXT:          .toc
 ; CHECK:               .dwsect 0x20000
 ; CHECK-NEXT:  L...dwline:
 ; CHECK-NEXT:  L..debug_line_0:
 ; CHECK-NEXT:  .set L..line_table_start0, L..debug_line_0-4
 ; CHECK-NEXT:          .vbyte  2, 3
-; CHECK-NEXT:          .vbyte  4, L..tmp9-L..tmp8
-; CHECK-NEXT:  L..tmp8:
+; CHECK-NEXT:          .vbyte  4, L..prologue_end0-L..prologue_start0
+; CHECK-NEXT:  L..prologue_start0:
 ; CHECK-NEXT:          .byte   4
 ; CHECK-NEXT:          .byte   1
 ; CHECK-NEXT:          .byte   -5
 ; CHECK-NEXT:          .byte   14
 ; CHECK-NEXT:          .byte   13
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   1
 ; CHECK-NEXT:          .byte   1

 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   '2,'.,'c
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   1
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   0
-; CHECK-NEXT:  L..tmp9:
+; CHECK-NEXT:  L..prologue_end0:
 ; CHECK-NEXT:          .byte   0                               # Set address to L..tmp0
 ; CHECK-NEXT:          .byte   5
 ; CHECK-NEXT:          .byte   2
 ; CHECK-NEXT:          .vbyte  4, L..tmp0
 ; CHECK-NEXT:          .byte   1                               # Start sequence
 ; CHECK-NEXT:          .byte   5
 ; CHECK-NEXT:          .byte   12
 ; CHECK-NEXT:          .byte   10

llvm/test/DebugInfo/XCOFF/function-sections.ll

 ; CHECK-NEXT:  L..info_string5:
 ; CHECK-NEXT:          .byte   'b,'a,'r,0000                   # string offset=39
 ; CHECK-NEXT:          .toc
 ; CHECK:               .dwsect 0x20000
 ; CHECK-NEXT:  L...dwline:
 ; CHECK-NEXT:  L..debug_line_0:
 ; CHECK-NEXT:  .set L..line_table_start0, L..debug_line_0-4
 ; CHECK-NEXT:          .vbyte  2, 3
-; CHECK-NEXT:          .vbyte  4, L..tmp7-L..tmp6
-; CHECK-NEXT:  L..tmp6:
+; CHECK-NEXT:          .vbyte  4, L..prologue_end0-L..prologue_start0
+; CHECK-NEXT:  L..prologue_start0:
 ; CHECK-NEXT:          .byte   4
 ; CHECK-NEXT:          .byte   1
 ; CHECK-NEXT:          .byte   -5
 ; CHECK-NEXT:          .byte   14
 ; CHECK-NEXT:          .byte   13
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   1
 ; CHECK-NEXT:          .byte   1

 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   '1,'.,'c
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   1
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   0
 ; CHECK-NEXT:          .byte   0
-; CHECK-NEXT:  L..tmp7:
+; CHECK-NEXT:  L..prologue_end0:
 ; CHECK-NEXT:          .byte   0                               # Set address to L..tmp0
 ; CHECK-NEXT:          .byte   5
 ; CHECK-NEXT:          .byte   2
 ; CHECK-NEXT:          .vbyte  4, L..tmp0
 ; CHECK-NEXT:          .byte   19                              # Start sequence
 ; CHECK-NEXT:          .byte   5
 ; CHECK-NEXT:          .byte   3
 ; CHECK-NEXT:          .byte   10