DebugInfo: Avoid creating unnecessary/empty line tables and remove the special case of '0' in DwarfCompileUnit::initStmtList by just always using a label difference

This moves one case of raw text checking down into the MCStreamer
interfaces in the form of a virtual function, even if we ultimately end
up consolidating on the one-or-many line tables issue one day, this is
nicer in the interim. This just generally streamlines a bunch of use
cases into a common code path.

llvm-svn: 205287

3 files changed, 20 insertions, 6 deletions

diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index fa54c1a8da1..884ccf9299a 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -207,6 +207,7 @@ public:
                              unsigned Column, unsigned Flags,
                              unsigned Isa, unsigned Discriminator,
                              StringRef FileName) override;
+  MCSymbol *getDwarfLineTableSymbol(unsigned CUID) override;
 
   void EmitIdent(StringRef IdentString) override;
   void EmitCFISections(bool EH, bool Debug) override;
@@ -957,6 +958,12 @@ void MCAsmStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
   EmitEOL();
 }
 
+MCSymbol *MCAsmStreamer::getDwarfLineTableSymbol(unsigned CUID) {
+  // Always use the zeroth line table, since asm syntax only supports one line
+  // table for now.
+  return MCStreamer::getDwarfLineTableSymbol(0);
+}
+
 void MCAsmStreamer::EmitIdent(StringRef IdentString) {
   assert(MAI->hasIdentDirective() && ".ident directive not supported");
   OS << "\t.ident\t";
@@ -1442,8 +1449,7 @@ void MCAsmStreamer::FinishImpl() {
   // directly, the label is the only work required here.
   auto &Tables = getContext().getMCDwarfLineTables();
   if (!Tables.empty()) {
-    // FIXME: assert Tables.size() == 1 here, except that's not currently true
-    // due to DwarfUnit.cpp:2074.
+    assert(Tables.size() == 1 && "asm output only supports one line table");
     if (auto *Label = Tables.begin()->second.getLabel()) {
       SwitchSection(getContext().getObjectFileInfo()->getDwarfLineSection());
       EmitLabel(Label);
diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index 231948eaff5..72836ff32ec 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -788,10 +788,8 @@ void MCGenDwarfInfo::Emit(MCStreamer *MCOS) {
   bool CreateDwarfSectionSymbols =
       AsmInfo->doesDwarfUseRelocationsAcrossSections();
   MCSymbol *LineSectionSymbol = nullptr;
-  if (CreateDwarfSectionSymbols) {
-    LineSectionSymbol = context.CreateTempSymbol();
-    context.setMCLineTableSymbol(LineSectionSymbol, 0);
-  }
+  if (CreateDwarfSectionSymbols)
+    LineSectionSymbol = MCOS->getDwarfLineTableSymbol(0);
   MCSymbol *AbbrevSectionSymbol = NULL;
   MCSymbol *InfoSectionSymbol = NULL;
   MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfInfoSection());
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 0558a58abfd..8fa55aa59e2 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -191,6 +191,16 @@ void MCStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                   Discriminator);
 }
 
+MCSymbol *MCStreamer::getDwarfLineTableSymbol(unsigned CUID) {
+  MCDwarfLineTable &Table = getContext().getMCDwarfLineTable(CUID);
+  if (!Table.getLabel()) {
+    StringRef Prefix = Context.getAsmInfo()->getPrivateGlobalPrefix();
+    Table.setLabel(
+        Context.GetOrCreateSymbol(Prefix + "line_table_start" + Twine(CUID)));
+  }
+  return Table.getLabel();
+}
+
 MCDwarfFrameInfo *MCStreamer::getCurrentFrameInfo() {
   if (FrameInfos.empty())
     return 0;