[DebugInfo] Only print a single blank line after an empty line table

[jhenderson]

Summary

rG84a9756 added an extra blank line at the end of any line table. However, a blank line is also printed after the line table header, which meant that two blank lines in a row were being printed after a header, if there were no rows. This patch defers the post-header blank line printing until it has been determined that there are rows to print.

[dblaikie]

Sounds good

llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp

void DWARFDebugLine::Sequence::reset() {
   Empty = true;
 }
 
 DWARFDebugLine::LineTable::LineTable() { clear(); }
 
 void DWARFDebugLine::LineTable::dump(raw_ostream &OS,
                                      DIDumpOptions DumpOptions) const {
   Prologue.dump(OS, DumpOptions);
-  OS << '\n';
 
   if (!Rows.empty()) {
+    OS << '\n';
     Row::dumpTableHeader(OS);
     for (const Row &R : Rows) {
       R.dump(OS);
     }
   }
 
   // Terminate the table with a final blank line to clearly delineate it from
   // later dumps.

llvm/test/tools/llvm-dwarfdump/X86/debug-line.s

 # CHECK-NEXT:      opcode_base: 2
 # CHECK-NEXT: standard_opcode_lengths[DW_LNS_copy] = 42
 # CHECK-NEXT: include_directories[  1] = "baz"
 # CHECK-NEXT: file_names[  1]:
 # CHECK-NEXT:            name: "foo.c"
 # CHECK-NEXT:       dir_index: 1
 # CHECK-NEXT:        mod_time: 0x00000011
 # CHECK-NEXT:          length: 0x00000022
-# CHECK-NOT:  {{.}}
+# CHECK-EMPTY:
+# CHECK-NEXT: debug_line[0x0000008c]
 
 .section .debug_line,"",@progbits
     .long .Lunit0_end - .Lunit0_begin ## unit_length
 .Lunit0_begin:
     .short 5 ## version
     .byte 8  ## address_size
     .byte 0  ## segment_selector_size
     .long .Lheader0_end - .Lheader0_begin ## header_length
.Lheader0_end:
     .byte 0x7  ## DW_LNS_set_basic_block
     .byte 0xA  ## DW_LNS_set_prologue_end
     .byte 0xB  ## DW_LNS_set_epilogue_begin
 
     .byte 0xD  ## DW_LNS_unknown - shows that unknown opcodes do not affect state.
     .byte 0, 0x1, 0x1 ## DW_LNE_end_sequence
 .Lunit0_end:
 
-## Second line table program with version 4.
+## Second line table program with version 4 and no sequences.
     .long .Lunit1_end - .Lunit1_begin ## unit_length
 .Lunit1_begin:
     .short 4 ## version
     .long .Lheader1_end - .Lheader1_begin ## header_length
 .Lheader1_begin:
     .byte 2  ## minimum_instruction_length
     .byte 4  ## maximum_operations_per_instruction
     .byte 0  ## default_is_stmt
     .byte 42 ## line_base
     .byte 10 ## line_range
     .byte 2  ## opcode_base - lower than normal to show this can be handled.
     .byte 42 ## standard_opcode_lengths - different to normal.
     ## include_directories
     .asciz "baz"
     .byte 0
     ## file_names
     .asciz "foo.c"
     .byte 1    ## Directory index
     .byte 0x11 ## Timestamp
     .byte 0x22 ## Length
 .Lheader1_end:
 .Lunit1_end:
+
+## Third line table program needed to show that only a single blank line is
+## printed after a program with no sequences. The values in this table are
+## arbitrary.
+    .long .Lunit2_end - .Lunit2_begin ## unit_length
+.Lunit2_begin:
+    .short 4 ## version
+    .long .Lheader2_end - .Lheader2_begin ## header_length
+.Lheader2_begin:
+    .byte 1 ## minimum_instruction_length
+    .byte 2 ## maximum_operations_per_instruction
+    .byte 1 ## default_is_stmt
+    .byte 1 ## line_base
+    .byte 1 ## line_range
+    .byte 2 ## opcode_base
+    .byte 1 ## standard_opcode_lengths
+    ## include_directories
+    .byte 0
+    ## file_names
+    .asciz "bar.c"
+    .byte 0 ## Directory index
+    .byte 0 ## Timestamp
+    .byte 0 ## Length
+.Lheader2_end:
+    .byte 0, 0x1, 0x1 ## DW_LNE_end_sequence
+.Lunit2_end: