DebugInfo: Avoid emitting standard opcode lengths in debug_line.dwo headers where opcodes are never used anyway

Introduce a slightly tighter wrapper around the header structure that
handles this use case. (MCDwarfDwoLineTable)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204101 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCDwarf.h

@@ -15,6 +15,7 @@
 #ifndef LLVM_MC_MCDWARF_H
 #define LLVM_MC_MCDWARF_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/MapVector.h"
@@ -187,6 +188,17 @@ struct MCDwarfLineTableHeader {
   unsigned getFile(StringRef &Directory, StringRef &FileName,
                    unsigned FileNumber = 0);
   std::pair<MCSymbol *, MCSymbol *> Emit(MCStreamer *MCOS) const;
+  std::pair<MCSymbol *, MCSymbol *>
+  Emit(MCStreamer *MCOS, ArrayRef<char> SpecialOpcodeLengths) const;
+};
+
+class MCDwarfDwoLineTable {
+  MCDwarfLineTableHeader Header;
+public:
+  unsigned getFile(StringRef Directory, StringRef FileName) {
+    return Header.getFile(Directory, FileName);
+  }
+  void Emit(MCStreamer &MCOS) const;
 };
 
 class MCDwarfLineTable {

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -2684,7 +2684,7 @@ void DwarfDebug::emitDebugLineDWO() {
   assert(useSplitDwarf() && "No split dwarf?");
   Asm->OutStreamer.SwitchSection(
       Asm->getObjFileLowering().getDwarfLineDWOSection());
-  Asm->OutStreamer.EmitLabel(SplitTypeUnitFileTable.Emit(&Asm->OutStreamer).second);
+  SplitTypeUnitFileTable.Emit(Asm->OutStreamer);
 }
 
 // Emit the .debug_str.dwo section for separated dwarf. This contains the

lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -489,7 +489,7 @@ class DwarfDebug : public AsmPrinterHandler {
 
   // Store file names for type units under fission in a line table header that
   // will be emitted into debug_line.dwo.
-  MCDwarfLineTableHeader SplitTypeUnitFileTable;
+  MCDwarfDwoLineTable SplitTypeUnitFileTable;
 
   void addScopeVariable(LexicalScope *LS, DbgVariable *Var);
 

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -57,7 +57,7 @@ DwarfCompileUnit::DwarfCompileUnit(unsigned UID, DIE *D, DICompileUnit Node,
 
 DwarfTypeUnit::DwarfTypeUnit(unsigned UID, DIE *D, DwarfCompileUnit &CU,
                              AsmPrinter *A, DwarfDebug *DW, DwarfFile *DWU,
-                             MCDwarfLineTableHeader *SplitLineTable)
+                             MCDwarfDwoLineTable *SplitLineTable)
     : DwarfUnit(UID, D, CU.getCUNode(), A, DW, DWU), CU(CU),
       SplitLineTable(SplitLineTable) {
   if (SplitLineTable)

lib/CodeGen/AsmPrinter/DwarfUnit.h

@@ -616,12 +616,12 @@ private:
   uint64_t TypeSignature;
   const DIE *Ty;
   DwarfCompileUnit &CU;
-  MCDwarfLineTableHeader *SplitLineTable;
+  MCDwarfDwoLineTable *SplitLineTable;
 
 public:
   DwarfTypeUnit(unsigned UID, DIE *D, DwarfCompileUnit &CU, AsmPrinter *A,
                 DwarfDebug *DW, DwarfFile *DWU,
-                MCDwarfLineTableHeader *SplitLineTable = nullptr);
+                MCDwarfDwoLineTable *SplitLineTable = nullptr);
 
   void setTypeSignature(uint64_t Signature) { TypeSignature = Signature; }
   uint64_t getTypeSignature() const { return TypeSignature; }

lib/MC/MCDwarf.cpp

@@ -224,7 +224,33 @@ const MCSymbol *MCDwarfLineTable::Emit(MCStreamer *MCOS) {
   return LineStartSym;
 }
 
+void MCDwarfDwoLineTable::Emit(MCStreamer &MCOS) const {
+  MCOS.EmitLabel(Header.Emit(&MCOS, None).second);
+}
+
 std::pair<MCSymbol *, MCSymbol *> MCDwarfLineTableHeader::Emit(MCStreamer *MCOS) const {
+  static const char StandardOpcodeLengths[] = {
+      0, // length of DW_LNS_copy
+      1, // length of DW_LNS_advance_pc
+      1, // length of DW_LNS_advance_line
+      1, // length of DW_LNS_set_file
+      1, // length of DW_LNS_set_column
+      0, // length of DW_LNS_negate_stmt
+      0, // length of DW_LNS_set_basic_block
+      0, // length of DW_LNS_const_add_pc
+      1, // length of DW_LNS_fixed_advance_pc
+      0, // length of DW_LNS_set_prologue_end
+      0, // length of DW_LNS_set_epilogue_begin
+      1  // DW_LNS_set_isa
+  };
+  assert(array_lengthof(StandardOpcodeLengths) == (DWARF2_LINE_OPCODE_BASE - 1));
+  return Emit(MCOS, StandardOpcodeLengths);
+}
+
+std::pair<MCSymbol *, MCSymbol *>
+MCDwarfLineTableHeader::Emit(MCStreamer *MCOS,
+                             ArrayRef<char> StandardOpcodeLengths) const {
+
   MCContext &context = MCOS->getContext();
 
   // Create a symbol at the beginning of the line table.
@@ -260,21 +286,11 @@ std::pair<MCSymbol *, MCSymbol *> MCDwarfLineTableHeader::Emit(MCStreamer *MCOS)
   MCOS->EmitIntValue(DWARF2_LINE_DEFAULT_IS_STMT, 1);
   MCOS->EmitIntValue(DWARF2_LINE_BASE, 1);
   MCOS->EmitIntValue(DWARF2_LINE_RANGE, 1);
-  MCOS->EmitIntValue(DWARF2_LINE_OPCODE_BASE, 1);
+  MCOS->EmitIntValue(StandardOpcodeLengths.size() + 1, 1);
 
   // Standard opcode lengths
-  MCOS->EmitIntValue(0, 1); // length of DW_LNS_copy
+  for (char Length : StandardOpcodeLengths)
-  MCOS->EmitIntValue(1, 1); // length of DW_LNS_advance_pc
+    MCOS->EmitIntValue(Length, 1);
-  MCOS->EmitIntValue(1, 1); // length of DW_LNS_advance_line
-  MCOS->EmitIntValue(1, 1); // length of DW_LNS_set_file
-  MCOS->EmitIntValue(1, 1); // length of DW_LNS_set_column
-  MCOS->EmitIntValue(0, 1); // length of DW_LNS_negate_stmt
-  MCOS->EmitIntValue(0, 1); // length of DW_LNS_set_basic_block
-  MCOS->EmitIntValue(0, 1); // length of DW_LNS_const_add_pc
-  MCOS->EmitIntValue(1, 1); // length of DW_LNS_fixed_advance_pc
-  MCOS->EmitIntValue(0, 1); // length of DW_LNS_set_prologue_end
-  MCOS->EmitIntValue(0, 1); // length of DW_LNS_set_epilogue_begin
-  MCOS->EmitIntValue(1, 1); // DW_LNS_set_isa
 
   // Put out the directory and file tables.
 

test/DebugInfo/X86/generate-odr-hash.ll

@@ -141,6 +141,8 @@
 
 ; CHECK-LABEL: .debug_line.dwo contents:
 ; FISSION: Line table prologue
+; FISSION: opcode_base: 1
+; FISSION-NOT: standard_opcode_lengths
 ; FISSION-NOT: file_names[
 ; FISSION: file_names{{.*}} bar.h
 ; FISSION: file_names{{.*}} bar.cpp