Dwarf: support for LTO where a single object file can have multiple line tables

We generate one line table for each compilation unit in the object file.
Reviewed by Eric and Kevin.

rdar://problem/13067005


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174445 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 61 insertions, 15 deletions

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 967c149b53..dcaab316b5 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -662,13 +662,21 @@ CompileUnit *DwarfDebug::constructCompileUnit(const MDNode *N) {
   // 2.17.1 requires that we use DW_AT_low_pc for a single entry point
   // into an entity. We're using 0 (or a NULL label) for this.
   NewCU->addLabelAddress(Die, dwarf::DW_AT_low_pc, NULL);
+
+  // Define start line table label for each Compile Unit.
+  MCSymbol *LineTableStartSym = Asm->GetTempSymbol("line_table_start",
+                                                   NewCU->getUniqueID());
+  Asm->OutStreamer.getContext().setMCLineTableSymbol(LineTableStartSym,
+                                                     NewCU->getUniqueID());
+
   // DW_AT_stmt_list is a offset of line number information for this
   // compile unit in debug_line section.
   if (Asm->MAI->doesDwarfUseRelocationsAcrossSections())
     NewCU->addLabel(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
-                    Asm->GetTempSymbol("section_line"));
+                    LineTableStartSym);
   else
-    NewCU->addUInt(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4, 0);
+    NewCU->addDelta(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
+                    LineTableStartSym, Asm->GetTempSymbol("section_line"));
 
   if (!CompilationDir.empty())
     NewCU->addString(Die, dwarf::DW_AT_comp_dir, CompilationDir);
@@ -1399,6 +1407,13 @@ void DwarfDebug::beginFunction(const MachineFunction *MF) {
   if (LScopes.empty()) return;
   identifyScopeMarkers();
 
+  // Set DwarfCompileUnitID in MCContext to the Compile Unit this function
+  // belongs to.
+  LexicalScope *FnScope = LScopes.getCurrentFunctionScope();
+  CompileUnit *TheCU = SPMap.lookup(FnScope->getScopeNode());
+  assert(TheCU && "Unable to find compile unit!");
+  Asm->OutStreamer.getContext().setDwarfCompileUnitID(TheCU->getUniqueID());
+
   FunctionBeginSym = Asm->GetTempSymbol("func_begin",
                                         Asm->getFunctionNumber());
   // Assumes in correct section after the entry point.
@@ -1583,6 +1598,8 @@ void DwarfDebug::endFunction(const MachineFunction *MF) {
                                       Asm->getFunctionNumber());
   // Assumes in correct section after the entry point.
   Asm->OutStreamer.EmitLabel(FunctionEndSym);
+  // Set DwarfCompileUnitID in MCContext to default value.
+  Asm->OutStreamer.getContext().setDwarfCompileUnitID(0);
 
   SmallPtrSet<const MDNode *, 16> ProcessedVars;
   collectVariableInfo(MF, ProcessedVars);
diff --git a/lib/MC/MCContext.cpp b/lib/MC/MCContext.cpp
index aa52b49047..a074003711 100644
--- a/lib/MC/MCContext.cpp
+++ b/lib/MC/MCContext.cpp
@@ -40,7 +40,7 @@ MCContext::MCContext(const MCAsmInfo &mai, const MCRegisterInfo &mri,
   CompilationDir(llvm::sys::Path::GetCurrentDirectory().str()),
   CurrentDwarfLoc(0,0,0,DWARF2_FLAG_IS_STMT,0,0), 
   DwarfLocSeen(false), GenDwarfForAssembly(false), GenDwarfFileNumber(0),
-  AllowTemporaryLabels(true), AutoReset(DoAutoReset) {
+  AllowTemporaryLabels(true), DwarfCompileUnitID(0), AutoReset(DoAutoReset) {
 
   MachOUniquingMap = 0;
   ELFUniquingMap = 0;
diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 3cf47bc6c5..5465af6385 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -101,7 +101,8 @@ void MCLineEntry::Make(MCStreamer *MCOS, const MCSection *Section) {
   }
 
   // Add the line entry to this section's entries.
-  LineSection->addLineEntry(LineEntry);
+  LineSection->addLineEntry(LineEntry,
+                            MCOS->getContext().getDwarfCompileUnitID());
 }
 
 //
@@ -131,7 +132,12 @@ static inline const MCExpr *MakeStartMinusEndExpr(const MCStreamer &MCOS,
 //
 static inline void EmitDwarfLineTable(MCStreamer *MCOS,
                                       const MCSection *Section,
-                                      const MCLineSection *LineSection) {
+                                      const MCLineSection *LineSection,
+                                      unsigned CUID) {
+  // This LineSection does not contain any LineEntry for the given Compile Unit.
+  if (!LineSection->containEntriesForID(CUID))
+    return;
+
   unsigned FileNum = 1;
   unsigned LastLine = 1;
   unsigned Column = 0;
@@ -141,8 +147,8 @@ static inline void EmitDwarfLineTable(MCStreamer *MCOS,
 
   // Loop through each MCLineEntry and encode the dwarf line number table.
   for (MCLineSection::const_iterator
-         it = LineSection->getMCLineEntries()->begin(),
-         ie = LineSection->getMCLineEntries()->end(); it != ie; ++it) {
+         it = LineSection->getMCLineEntries(CUID).begin(),
+         ie = LineSection->getMCLineEntries(CUID).end(); it != ie; ++it) {
 
     if (FileNum != it->getFileNum()) {
       FileNum = it->getFileNum();
@@ -215,9 +221,36 @@ const MCSymbol *MCDwarfFileTable::Emit(MCStreamer *MCOS) {
   // Switch to the section where the table will be emitted into.
   MCOS->SwitchSection(context.getObjectFileInfo()->getDwarfLineSection());
 
-  // Create a symbol at the beginning of this section.
-  MCSymbol *LineStartSym = context.CreateTempSymbol();
-  // Set the value of the symbol, as we are at the start of the section.
+  const DenseMap<unsigned, MCSymbol *> &MCLineTableSymbols =
+    MCOS->getContext().getMCLineTableSymbols();
+  // CUID and MCLineTableSymbols are set in DwarfDebug, when DwarfDebug does
+  // not exist, CUID will be 0 and MCLineTableSymbols will be empty.
+  // Handle Compile Unit 0, the line table start symbol is the section symbol.
+  const MCSymbol *LineStartSym = EmitCU(MCOS, 0);
+  // Handle the rest of the Compile Units.
+  for (unsigned Is = 1, Ie = MCLineTableSymbols.size(); Is < Ie; Is++)
+    EmitCU(MCOS, Is);
+
+  // Now delete the MCLineSections that were created in MCLineEntry::Make()
+  // and used to emit the line table.
+  const DenseMap<const MCSection *, MCLineSection *> &MCLineSections =
+    MCOS->getContext().getMCLineSections();
+  for (DenseMap<const MCSection *, MCLineSection *>::const_iterator it =
+       MCLineSections.begin(), ie = MCLineSections.end(); it != ie;
+       ++it)
+    delete it->second;
+
+  return LineStartSym;
+}
+
+const MCSymbol *MCDwarfFileTable::EmitCU(MCStreamer *MCOS, unsigned CUID) {
+  MCContext &context = MCOS->getContext();
+
+  // Create a symbol at the beginning of the line table.
+  MCSymbol *LineStartSym = MCOS->getContext().getMCLineTableSymbol(CUID);
+  if (!LineStartSym)
+    LineStartSym = context.CreateTempSymbol();
+  // Set the value of the symbol, as we are at the start of the line table.
   MCOS->EmitLabel(LineStartSym);
 
   // Create a symbol for the end of the section (to be set when we get there).
@@ -301,11 +334,7 @@ const MCSymbol *MCDwarfFileTable::Emit(MCStreamer *MCOS) {
        ++it) {
     const MCSection *Sec = *it;
     const MCLineSection *Line = MCLineSections.lookup(Sec);
-    EmitDwarfLineTable(MCOS, Sec, Line);
-
-    // Now delete the MCLineSections that were created in MCLineEntry::Make()
-    // and used to emit the line table.
-    delete Line;
+    EmitDwarfLineTable(MCOS, Sec, Line, CUID);
   }
 
   if (MCOS->getContext().getAsmInfo().getLinkerRequiresNonEmptyDwarfLines()