From 35d2f6151024a63b4bf84730aaa88e34413a8220 Mon Sep 17 00:00:00 2001
From: David Blaikie <dblaikie@gmail.com>
Date: Fri, 14 Feb 2014 01:57:59 +0000
Subject: [PATCH] DebugInfo: Don't include the name of the CU file in the line
 table file list when it's unneeded

Recommitting r201351 and r201355 (reverted in r201351 and r201355)

We weren't emitting the an empty (header only) line table when the line
table was empty - this made the DWARF invalid (the compile unit would
point to the zero-size debug_lines section where there should've been an
empty line table but there was nothing at all). Fix that, and as a
consequence this works around/addresses PR18809.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201380 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/AsmPrinter/DwarfDebug.cpp   |  3 ---
 lib/MC/MCObjectStreamer.cpp             |  3 ++-
 test/DebugInfo/X86/generate-odr-hash.ll |  8 ++++++++
 test/DebugInfo/empty.ll                 | 20 ++++++++++++++++++++
 4 files changed, 30 insertions(+), 4 deletions(-)
 create mode 100644 test/DebugInfo/empty.ll

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index de2f4c6e02a..4d0eb445d34 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -756,9 +756,6 @@ DwarfCompileUnit *DwarfDebug::constructDwarfCompileUnit(DICompileUnit DIUnit) {
   InfoHolder.addUnit(NewCU);
 
   FileIDCUMap[NewCU->getUniqueID()] = 0;
-  // Call this to emit a .file directive if it wasn't emitted for the source
-  // file this CU comes from yet.
-  getOrCreateSourceID(FN, CompilationDir, NewCU->getUniqueID());
 
   NewCU->addString(Die, dwarf::DW_AT_producer, DIUnit.getProducer());
   NewCU->addUInt(Die, dwarf::DW_AT_language, dwarf::DW_FORM_data2,
diff --git a/lib/MC/MCObjectStreamer.cpp b/lib/MC/MCObjectStreamer.cpp
index f00231e3d31..bfa3c8cfa34 100644
--- a/lib/MC/MCObjectStreamer.cpp
+++ b/lib/MC/MCObjectStreamer.cpp
@@ -379,7 +379,8 @@ void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
 void MCObjectStreamer::FinishImpl() {
   // Dump out the dwarf file & directory tables and line tables.
   const MCSymbol *LineSectionSymbol = NULL;
-  if (getContext().hasDwarfFiles())
+  if (!getContext().getMCLineTableSymbols().empty() ||
+      getContext().hasDwarfFiles())
     LineSectionSymbol = MCDwarfFileTable::Emit(this);
 
   // If we are generating dwarf for assembly source files dump out the sections.
diff --git a/test/DebugInfo/X86/generate-odr-hash.ll b/test/DebugInfo/X86/generate-odr-hash.ll
index 6ddb54e5eef..e7b62104dfb 100644
--- a/test/DebugInfo/X86/generate-odr-hash.ll
+++ b/test/DebugInfo/X86/generate-odr-hash.ll
@@ -125,6 +125,14 @@
 ; CHECK: DW_TAG_member
 ; CHECK-NEXT: DW_AT_name{{.*}}"a"
 
+; CHECK-LABEL: .debug_line contents:
+; CHECK: Line table prologue
+; CHECK-NOT: file_names[
+; CHECK: file_names{{.*}} bar.h
+; CHECK: file_names{{.*}} bar.cpp
+; CHECK-NOT: file_names[
+; CHECK-LABEL: .debug_str contents:
+
 ; Use the unit size as a rough hash/identifier for the unit we're dealing with
 ; it happens to be unambiguous at the moment, but it's hardly ideal.
 ; CHECK-LABEL: .debug_pubtypes contents:
diff --git a/test/DebugInfo/empty.ll b/test/DebugInfo/empty.ll
new file mode 100644
index 00000000000..9f4836ff0d5
--- /dev/null
+++ b/test/DebugInfo/empty.ll
@@ -0,0 +1,20 @@
+; RUN: llc %s -o %t -filetype=obj
+; RUN: llvm-dwarfdump -debug-dump=line %t | FileCheck %s
+
+; PR18809
+; XFAIL: cygwin,mingw32
+
+; Expect no line table entry since there are no functions and file references in this compile unit
+; CHECK: .debug_line contents:
+; CHECK: Line table prologue:
+; CHECK: total_length: 0x00000019
+; CHECK-NOT: file_names[
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!5}
+
+!0 = metadata !{i32 720913, metadata !4, i32 12, metadata !"clang version 3.1 (trunk 143523)", i1 true, metadata !"", i32 0, metadata !2, metadata !2, metadata !2, metadata !2, null, metadata !""} ; [ DW_TAG_compile_unit ]
+!2 = metadata !{}
+!3 = metadata !{i32 786473, metadata !4} ; [ DW_TAG_file_type ]
+!4 = metadata !{metadata !"empty.c", metadata !"/home/nlewycky"}
+!5 = metadata !{i32 1, metadata !"Debug Info Version", i32 1}