[debug-info] refactor emitDwarfUnitLength

remove `Hi` `Lo` argument from `emitDwarfUnitLength`, so we
can make caller of emitDwarfUnitLength easier.

Reviewed By: MaskRay, dblaikie, ikudrin

Differential Revision: https://reviews.llvm.org/D96409

Author: Chen Zheng

llvm/include/llvm/CodeGen/AsmPrinter.h

@@ -645,8 +645,9 @@ class AsmPrinter : public MachineFunctionPass {
 
   /// Emit a unit length field. The actual format, DWARF32 or DWARF64, is chosen
   /// according to the settings.
-  void emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
-                           const Twine &Comment) const;
+  /// Return the end symbol generated inside, the caller needs to emit it.
+  MCSymbol *emitDwarfUnitLength(const Twine &Prefix,
+                                const Twine &Comment) const;
 
   /// Emit reference to a call site with a specified encoding
   void emitCallSiteOffset(const MCSymbol *Hi, const MCSymbol *Lo,

llvm/include/llvm/MC/MCStreamer.h

@@ -1089,8 +1089,9 @@ class MCStreamer {
 
   /// Emit a unit length field. The actual format, DWARF32 or DWARF64, is chosen
   /// according to the settings.
-  virtual void emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
-                                   const Twine &Comment);
+  /// Return the end symbol generated inside, the caller needs to emit it.
+  virtual MCSymbol *emitDwarfUnitLength(const Twine &Prefix,
+                                        const Twine &Comment);
 };
 
 /// Create a dummy machine code streamer, which does nothing. This is useful for

llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp

@@ -205,7 +205,7 @@ class Dwarf5AccelTableWriter : public AccelTableWriter {
         : CompUnitCount(CompUnitCount), BucketCount(BucketCount),
           NameCount(NameCount) {}
 
-    void emit(const Dwarf5AccelTableWriter &Ctx) const;
+    void emit(Dwarf5AccelTableWriter &Ctx);
   };
   struct AttributeEncoding {
     dwarf::Index Index;
@@ -216,8 +216,7 @@ class Dwarf5AccelTableWriter : public AccelTableWriter {
   DenseMap<uint32_t, SmallVector<AttributeEncoding, 2>> Abbreviations;
   ArrayRef<MCSymbol *> CompUnits;
   llvm::function_ref<unsigned(const DataT &)> getCUIndexForEntry;
-  MCSymbol *ContributionStart = Asm->createTempSymbol("names_start");
-  MCSymbol *ContributionEnd = Asm->createTempSymbol("names_end");
+  MCSymbol *ContributionEnd = nullptr;
   MCSymbol *AbbrevStart = Asm->createTempSymbol("names_abbrev_start");
   MCSymbol *AbbrevEnd = Asm->createTempSymbol("names_abbrev_end");
   MCSymbol *EntryPool = Asm->createTempSymbol("names_entries");
@@ -240,7 +239,7 @@ class Dwarf5AccelTableWriter : public AccelTableWriter {
       ArrayRef<MCSymbol *> CompUnits,
       llvm::function_ref<unsigned(const DataT &)> GetCUIndexForEntry);
 
-  void emit() const;
+  void emit();
 };
 } // namespace
 
@@ -361,14 +360,12 @@ void AppleAccelTableWriter::emit() const {
 }
 
 template <typename DataT>
-void Dwarf5AccelTableWriter<DataT>::Header::emit(
-    const Dwarf5AccelTableWriter &Ctx) const {
+void Dwarf5AccelTableWriter<DataT>::Header::emit(Dwarf5AccelTableWriter &Ctx) {
   assert(CompUnitCount > 0 && "Index must have at least one CU.");
 
   AsmPrinter *Asm = Ctx.Asm;
-  Asm->emitDwarfUnitLength(Ctx.ContributionEnd, Ctx.ContributionStart,
-                           "Header: unit length");
-  Asm->OutStreamer->emitLabel(Ctx.ContributionStart);
+  Ctx.ContributionEnd =
+      Asm->emitDwarfUnitLength("names", "Header: unit length");
   Asm->OutStreamer->AddComment("Header: version");
   Asm->emitInt16(Version);
   Asm->OutStreamer->AddComment("Header: padding");
@@ -526,7 +523,7 @@ Dwarf5AccelTableWriter<DataT>::Dwarf5AccelTableWriter(
     Abbreviations.try_emplace(Tag, UniformAttributes);
 }
 
-template <typename DataT> void Dwarf5AccelTableWriter<DataT>::emit() const {
+template <typename DataT> void Dwarf5AccelTableWriter<DataT>::emit() {
   Header.emit(*this);
   emitCUList();
   emitBuckets();

llvm/lib/CodeGen/AsmPrinter/AddressPool.cpp

@@ -25,12 +25,9 @@ unsigned AddressPool::getIndex(const MCSymbol *Sym, bool TLS) {
 
 MCSymbol *AddressPool::emitHeader(AsmPrinter &Asm, MCSection *Section) {
   static const uint8_t AddrSize = Asm.getDataLayout().getPointerSize();
-  StringRef Prefix = "debug_addr_";
-  MCSymbol *BeginLabel = Asm.createTempSymbol(Prefix + "start");
-  MCSymbol *EndLabel = Asm.createTempSymbol(Prefix + "end");
 
-  Asm.emitDwarfUnitLength(EndLabel, BeginLabel, "Length of contribution");
-  Asm.OutStreamer->emitLabel(BeginLabel);
+  MCSymbol *EndLabel =
+      Asm.emitDwarfUnitLength("debug_addr", "Length of contribution");
   Asm.OutStreamer->AddComment("DWARF version number");
   Asm.emitInt16(Asm.getDwarfVersion());
   Asm.OutStreamer->AddComment("Address size");

llvm/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp

@@ -203,9 +203,9 @@ void AsmPrinter::emitDwarfUnitLength(uint64_t Length,
   OutStreamer->emitDwarfUnitLength(Length, Comment);
 }
 
-void AsmPrinter::emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
-                                     const Twine &Comment) const {
-  OutStreamer->emitDwarfUnitLength(Hi, Lo, Comment);
+MCSymbol *AsmPrinter::emitDwarfUnitLength(const Twine &Prefix,
+                                          const Twine &Comment) const {
+  return OutStreamer->emitDwarfUnitLength(Prefix, Comment);
 }
 
 void AsmPrinter::emitCallSiteOffset(const MCSymbol *Hi, const MCSymbol *Lo,

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -2374,12 +2374,8 @@ void DwarfDebug::emitDebugPubSection(bool GnuStyle, StringRef Name,
     TheU = Skeleton;
 
   // Emit the header.
-  MCSymbol *BeginLabel = Asm->createTempSymbol("pub" + Name + "_begin");
-  MCSymbol *EndLabel = Asm->createTempSymbol("pub" + Name + "_end");
-  Asm->emitDwarfUnitLength(EndLabel, BeginLabel,
-                           "Length of Public " + Name + " Info");
-
-  Asm->OutStreamer->emitLabel(BeginLabel);
+  MCSymbol *EndLabel = Asm->emitDwarfUnitLength(
+      "pub" + Name, "Length of Public " + Name + " Info");
 
   Asm->OutStreamer->AddComment("DWARF Version");
   Asm->emitInt16(dwarf::DW_PUBNAMES_VERSION);

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -1701,13 +1701,10 @@ DIE *DwarfUnit::getOrCreateStaticMemberDIE(const DIDerivedType *DT) {
 
 void DwarfUnit::emitCommonHeader(bool UseOffsets, dwarf::UnitType UT) {
   // Emit size of content not including length itself
-  if (!DD->useSectionsAsReferences()) {
-    StringRef Prefix = isDwoUnit() ? "debug_info_dwo_" : "debug_info_";
-    MCSymbol *BeginLabel = Asm->createTempSymbol(Prefix + "start");
-    EndLabel = Asm->createTempSymbol(Prefix + "end");
-    Asm->emitDwarfUnitLength(EndLabel, BeginLabel, "Length of Unit");
-    Asm->OutStreamer->emitLabel(BeginLabel);
-  } else
+  if (!DD->useSectionsAsReferences())
+    EndLabel = Asm->emitDwarfUnitLength(
+        isDwoUnit() ? "debug_info_dwo" : "debug_info", "Length of Unit");
+  else
     Asm->emitDwarfUnitLength(getHeaderSize() + getUnitDie().getSize(),
                              "Length of Unit");
 

llvm/lib/MC/MCStreamer.cpp

@@ -1006,12 +1006,19 @@ void MCStreamer::emitDwarfUnitLength(uint64_t Length, const Twine &Comment) {
   emitIntValue(Length, dwarf::getDwarfOffsetByteSize(Context.getDwarfFormat()));
 }
 
-void MCStreamer::emitDwarfUnitLength(const MCSymbol *Hi, const MCSymbol *Lo,
-                                     const Twine &Comment) {
+MCSymbol *MCStreamer::emitDwarfUnitLength(const Twine &Prefix,
+                                          const Twine &Comment) {
   maybeEmitDwarf64Mark();
   AddComment(Comment);
+  MCSymbol *Lo = Context.createTempSymbol(Prefix + "_start");
+  MCSymbol *Hi = Context.createTempSymbol(Prefix + "_end");
+
   emitAbsoluteSymbolDiff(
       Hi, Lo, dwarf::getDwarfOffsetByteSize(Context.getDwarfFormat()));
+  // emit the begin symbol after we generate the length field.
+  emitLabel(Lo);
+  // Return the Hi symbol to the caller.
+  return Hi;
 }
 
 void MCStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {

llvm/test/DebugInfo/X86/dwarf-pubnames-split.ll

@@ -7,7 +7,7 @@
 
 ; Check that we get a symbol off of the debug_info section when using split dwarf and pubnames.
 
-; CHECK: .LpubTypes_begin0:
+; CHECK: .LpubTypes_start0:
 ; CHECK-NEXT: .short    2                       # DWARF Version
 ; CHECK-NEXT: .long     .Lcu_begin0             # Offset of Compilation Unit Info
 

llvm/unittests/CodeGen/AsmPrinterDwarfTest.cpp

@@ -50,19 +50,21 @@ class AsmPrinterEmitDwarfSymbolReferenceTest : public AsmPrinterFixtureBase {
     if (!AsmPrinterFixtureBase::init(TripleStr, DwarfVersion, DwarfFormat))
       return false;
 
-    // Create a symbol which will be emitted in the tests and associate it
-    // with a section because that is required in some code paths.
+    // AsmPrinter::emitDwarfSymbolReference(Label, true) gets the associated
+    // section from `Label` to find its BeginSymbol.
+    // Prepare the test symbol `Val` accordingly.
 
     Val = TestPrinter->getCtx().createTempSymbol();
-    Sec = TestPrinter->getCtx().getELFSection(".tst", ELF::SHT_PROGBITS, 0);
+    MCSection *Sec =
+        TestPrinter->getCtx().getELFSection(".tst", ELF::SHT_PROGBITS, 0);
     SecBeginSymbol = Sec->getBeginSymbol();
     TestPrinter->getMS().SwitchSection(Sec);
-    TestPrinter->getMS().emitLabel(Val);
+    Val->setFragment(&Sec->getDummyFragment());
+
     return true;
   }
 
   MCSymbol *Val = nullptr;
-  MCSection *Sec = nullptr;
   MCSymbol *SecBeginSymbol = nullptr;
 };
 
@@ -326,32 +328,49 @@ class AsmPrinterEmitDwarfUnitLengthAsHiLoDiffTest
     if (!AsmPrinterFixtureBase::init(TripleStr, DwarfVersion, DwarfFormat))
       return false;
 
-    Hi = TestPrinter->getCtx().createTempSymbol();
-    Lo = TestPrinter->getCtx().createTempSymbol();
     return true;
   }
-
-  MCSymbol *Hi = nullptr;
-  MCSymbol *Lo = nullptr;
 };
 
 TEST_F(AsmPrinterEmitDwarfUnitLengthAsHiLoDiffTest, DWARF32) {
   if (!init("x86_64-pc-linux", /*DwarfVersion=*/4, dwarf::DWARF32))
     return;
 
-  EXPECT_CALL(TestPrinter->getMS(), emitAbsoluteSymbolDiff(Hi, Lo, 4));
-  TestPrinter->getAP()->emitDwarfUnitLength(Hi, Lo, "");
+  InSequence S;
+  const MCSymbol *Hi = nullptr;
+  const MCSymbol *Lo = nullptr;
+  EXPECT_CALL(TestPrinter->getMS(), emitAbsoluteSymbolDiff(_, _, 4))
+      .WillOnce(DoAll(SaveArg<0>(&Hi), SaveArg<1>(&Lo)));
+  MCSymbol *LTmp = nullptr;
+  EXPECT_CALL(TestPrinter->getMS(), emitLabel(_, _))
+      .WillOnce(SaveArg<0>(&LTmp));
+
+  MCSymbol *HTmp = TestPrinter->getAP()->emitDwarfUnitLength("", "");
+  EXPECT_NE(Lo, nullptr);
+  EXPECT_EQ(Lo, LTmp);
+  EXPECT_NE(Hi, nullptr);
+  EXPECT_EQ(Hi, HTmp);
 }
 
 TEST_F(AsmPrinterEmitDwarfUnitLengthAsHiLoDiffTest, DWARF64) {
   if (!init("x86_64-pc-linux", /*DwarfVersion=*/4, dwarf::DWARF64))
     return;
 
   InSequence S;
+  const MCSymbol *Hi = nullptr;
+  const MCSymbol *Lo = nullptr;
   EXPECT_CALL(TestPrinter->getMS(), emitIntValue(dwarf::DW_LENGTH_DWARF64, 4));
-  EXPECT_CALL(TestPrinter->getMS(), emitAbsoluteSymbolDiff(Hi, Lo, 8));
-
-  TestPrinter->getAP()->emitDwarfUnitLength(Hi, Lo, "");
+  EXPECT_CALL(TestPrinter->getMS(), emitAbsoluteSymbolDiff(_, _, 8))
+      .WillOnce(DoAll(SaveArg<0>(&Hi), SaveArg<1>(&Lo)));
+  MCSymbol *LTmp = nullptr;
+  EXPECT_CALL(TestPrinter->getMS(), emitLabel(_, _))
+      .WillOnce(SaveArg<0>(&LTmp));
+
+  MCSymbol *HTmp = TestPrinter->getAP()->emitDwarfUnitLength("", "");
+  EXPECT_NE(Lo, nullptr);
+  EXPECT_EQ(Lo, LTmp);
+  EXPECT_NE(Hi, nullptr);
+  EXPECT_EQ(Hi, HTmp);
 }
 
 class AsmPrinterHandlerTest : public AsmPrinterFixtureBase {