Add support for having multiple sections with the same name and comdat.

Using this in combination with -ffunction-sections allows LLVM to output a .o
file with mulitple sections named .text. This saves space by avoiding long
unique names of the form .text.<C++ mangled name>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228980 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/CommandFlags.h

@@ -207,6 +207,10 @@ FunctionSections("function-sections",
                  cl::desc("Emit functions into separate sections"),
                  cl::init(false));
 
+cl::opt<bool> UniqueSectionNames("unique-section-names",
+                                 cl::desc("Give unique names to every section"),
+                                 cl::init(true));
+
 cl::opt<llvm::JumpTable::JumpTableType>
 JTableType("jump-table-type",
           cl::desc("Choose the type of Jump-Instruction Table for jumptable."),
@@ -284,6 +288,7 @@ static inline TargetOptions InitTargetOptionsFromCodeGenFlags() {
   Options.UseInitArray = !UseCtors;
   Options.DataSections = DataSections;
   Options.FunctionSections = FunctionSections;
+  Options.UniqueSectionNames = UniqueSectionNames;
 
   Options.MCOptions = InitMCTargetOptionsFromFlags();
   Options.JTType = JTableType;

include/llvm/MC/MCContext.h

@@ -277,6 +277,10 @@ namespace llvm {
                                       unsigned Flags, unsigned EntrySize,
                                       StringRef Group);
 
+    const MCSectionELF *getELFSection(StringRef Section, unsigned Type,
+                                      unsigned Flags, unsigned EntrySize,
+                                      StringRef Group, bool Unique);
+
     void renameELFSection(const MCSectionELF *Section, StringRef Name);
 
     const MCSectionELF *CreateELFGroupSection();

include/llvm/MC/MCSectionELF.h

@@ -39,6 +39,8 @@ class MCSectionELF : public MCSection {
   /// below.
   unsigned Flags;
 
+  bool Unique;
+
   /// EntrySize - The size of each entry in this section. This size only
   /// makes sense for sections that contain fixed-sized entries. If a
   /// section does not contain fixed-sized entries 'EntrySize' will be 0.
@@ -48,10 +50,10 @@ class MCSectionELF : public MCSection {
 
 private:
   friend class MCContext;
-  MCSectionELF(StringRef Section, unsigned type, unsigned flags,
+  MCSectionELF(StringRef Section, unsigned type, unsigned flags, SectionKind K,
-               SectionKind K, unsigned entrySize, const MCSymbol *group)
+               unsigned entrySize, const MCSymbol *group, bool Unique)
       : MCSection(SV_ELF, K), SectionName(Section), Type(type), Flags(flags),
-      EntrySize(entrySize), Group(group) {}
+        Unique(Unique), EntrySize(entrySize), Group(group) {}
   ~MCSectionELF();
 
   void setSectionName(StringRef Name) { SectionName = Name; }

include/llvm/Target/TargetMachine.h

@@ -171,6 +171,8 @@ public:
     return Options.MCOptions.AsmVerbose;
   }
 
+  bool getUniqueSectionNames() const { return Options.UniqueSectionNames; }
+
   /// Return true if data objects should be emitted into their own section,
   /// corresponds to -fdata-sections.
   bool getDataSections() const {

include/llvm/Target/TargetOptions.h

@@ -78,8 +78,8 @@ namespace llvm {
           EnableFastISel(false), PositionIndependentExecutable(false),
           UseInitArray(false), DisableIntegratedAS(false),
           CompressDebugSections(false), FunctionSections(false),
-          DataSections(false), TrapUnreachable(false), TrapFuncName(),
+          DataSections(false), UniqueSectionNames(true), TrapUnreachable(false),
-          FloatABIType(FloatABI::Default),
+          TrapFuncName(), FloatABIType(FloatABI::Default),
           AllowFPOpFusion(FPOpFusion::Standard), JTType(JumpTable::Single),
           FCFI(false), ThreadModel(ThreadModel::POSIX),
           CFIType(CFIntegrity::Sub), CFIEnforcing(false), CFIFuncName() {}
@@ -198,6 +198,8 @@ namespace llvm {
     /// Emit data into separate sections.
     unsigned DataSections : 1;
 
+    unsigned UniqueSectionNames : 1;
+
     /// Emit target-specific trap instruction for 'unreachable' IR instructions.
     unsigned TrapUnreachable : 1;
 

lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -228,25 +228,25 @@ const MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
 /// DataSections.
 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
   if (Kind.isText())
-    return ".text.";
+    return ".text";
   if (Kind.isReadOnly())
-    return ".rodata.";
+    return ".rodata";
   if (Kind.isBSS())
-    return ".bss.";
+    return ".bss";
   if (Kind.isThreadData())
-    return ".tdata.";
+    return ".tdata";
   if (Kind.isThreadBSS())
-    return ".tbss.";
+    return ".tbss";
   if (Kind.isDataNoRel())
-    return ".data.";
+    return ".data";
   if (Kind.isDataRelLocal())
-    return ".data.rel.local.";
+    return ".data.rel.local";
   if (Kind.isDataRel())
-    return ".data.rel.";
+    return ".data.rel";
   if (Kind.isReadOnlyWithRelLocal())
-    return ".data.rel.ro.local.";
+    return ".data.rel.ro.local";
   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
-  return ".data.rel.ro.";
+  return ".data.rel.ro";
 }
 
 const MCSection *TargetLoweringObjectFileELF::
@@ -268,16 +268,19 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
     StringRef Prefix = getSectionPrefixForGlobal(Kind);
 
     SmallString<128> Name(Prefix);
+    bool UniqueSectionNames = TM.getUniqueSectionNames();
+    if (UniqueSectionNames) {
+      Name.push_back('.');
       TM.getNameWithPrefix(Name, GV, Mang, true);
-
+    }
     StringRef Group = "";
     if (const Comdat *C = getELFComdat(GV)) {
       Flags |= ELF::SHF_GROUP;
       Group = C->getName();
     }
 
-    return getContext().getELFSection(
+    return getContext().getELFSection(Name, getELFSectionType(Name, Kind),
-        Name.str(), getELFSectionType(Name.str(), Kind), Flags, 0, Group);
+                                      Flags, 0, Group, !UniqueSectionNames);
   }
 
   if (Kind.isText()) return TextSection;

lib/MC/ELFObjectWriter.cpp

@@ -1151,7 +1151,7 @@ ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
 
   const MCSectionELF *RelaSection = Ctx.getELFSection(
       RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
-      Flags, EntrySize, Group);
+      Flags, EntrySize, Group, true);
   return &Asm.getOrCreateSectionData(*RelaSection);
 }
 

lib/MC/MCContext.cpp

@@ -272,12 +272,13 @@ void MCContext::renameELFSection(const MCSectionELF *Section, StringRef Name) {
 
 const MCSectionELF *MCContext::getELFSection(StringRef Section, unsigned Type,
                                              unsigned Flags, unsigned EntrySize,
-                                             StringRef Group) {
+                                             StringRef Group, bool Unique) {
   // Do the lookup, if we have a hit, return it.
   auto IterBool = ELFUniquingMap.insert(
       std::make_pair(SectionGroupPair(Section, Group), nullptr));
   auto &Entry = *IterBool.first;
-  if (!IterBool.second) return Entry.second;
+  if (!IterBool.second && !Unique)
+    return Entry.second;
 
   MCSymbol *GroupSym = nullptr;
   if (!Group.empty())
@@ -292,15 +293,22 @@ const MCSectionELF *MCContext::getELFSection(StringRef Section, unsigned Type,
     Kind = SectionKind::getReadOnly();
 
   MCSectionELF *Result = new (*this)
-      MCSectionELF(CachedName, Type, Flags, Kind, EntrySize, GroupSym);
+      MCSectionELF(CachedName, Type, Flags, Kind, EntrySize, GroupSym, Unique);
+  if (!Unique)
     Entry.second = Result;
   return Result;
 }
 
+const MCSectionELF *MCContext::getELFSection(StringRef Section, unsigned Type,
+                                             unsigned Flags, unsigned EntrySize,
+                                             StringRef Group) {
+  return getELFSection(Section, Type, Flags, EntrySize, Group, false);
+}
+
 const MCSectionELF *MCContext::CreateELFGroupSection() {
   MCSectionELF *Result =
       new (*this) MCSectionELF(".group", ELF::SHT_GROUP, 0,
-                             SectionKind::getReadOnly(), 4, nullptr);
+                               SectionKind::getReadOnly(), 4, nullptr, false);
   return Result;
 }
 

lib/MC/MCParser/ELFAsmParser.cpp

@@ -378,6 +378,8 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
   unsigned Flags = 0;
   const MCExpr *Subsection = nullptr;
   bool UseLastGroup = false;
+  StringRef UniqueStr;
+  bool Unique = false;
 
   // Set the defaults first.
   if (SectionName == ".fini" || SectionName == ".init" ||
@@ -462,6 +464,14 @@ bool ELFAsmParser::ParseSectionArguments(bool IsPush, SMLoc loc) {
             return TokError("Linkage must be 'comdat'");
         }
       }
+      if (getLexer().is(AsmToken::Comma)) {
+        Lex();
+        if (getParser().parseIdentifier(UniqueStr))
+          return TokError("expected identifier in directive");
+        if (UniqueStr != "unique")
+          return TokError("expected 'unique'");
+        Unique = true;
+      }
     }
   }
 
@@ -509,8 +519,8 @@ EndStmt:
       }
   }
 
-  const MCSection *ELFSection =
+  const MCSection *ELFSection = getContext().getELFSection(
-      getContext().getELFSection(SectionName, Type, Flags, Size, GroupName);
+      SectionName, Type, Flags, Size, GroupName, Unique);
   getStreamer().SwitchSection(ELFSection, Subsection);
 
   if (getContext().getGenDwarfForAssembly()) {

lib/MC/MCSectionELF.cpp

@@ -24,6 +24,9 @@ MCSectionELF::~MCSectionELF() {} // anchor.
 bool MCSectionELF::ShouldOmitSectionDirective(StringRef Name,
                                               const MCAsmInfo &MAI) const {
 
+  if (Unique)
+    return false;
+
   // FIXME: Does .section .bss/.data/.text work everywhere??
   if (Name == ".text" || Name == ".data" ||
       (Name == ".bss" && !MAI.usesELFSectionDirectiveForBSS()))
@@ -144,6 +147,10 @@ void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI,
     printName(OS, Group->getName());
     OS << ",comdat";
   }
+
+  if (Unique)
+    OS << ",unique";
+
   OS << '\n';
 
   if (Subsection)

test/CodeGen/X86/non-unique-sections.ll

@@ -0,0 +1,15 @@
+; RUN: llc < %s -mtriple=x86_64-pc-linux -function-sections -unique-section-names=false | FileCheck %s
+
+; CHECK:   .section                      .text,"ax",@progbits,unique
+; CHECK-NOT: section
+; CHECK: f:
+define void @f() {
+  ret void
+}
+
+; CHECK:   .section                      .text,"ax",@progbits,unique
+; CHECK-NOT: section
+; CHECK: g:
+define void @g() {
+  ret void
+}

test/MC/ELF/section-unique.s

@@ -0,0 +1,39 @@
+// RUN: llvm-mc -triple x86_64-pc-linux-gnu %s -o - | FileCheck %s
+// RUN: llvm-mc -triple x86_64-pc-linux-gnu %s -filetype=obj -o - | llvm-readobj -t | FileCheck %s --check-prefix=OBJ
+
+	.section	.text,"ax",@progbits,unique
+        .globl	f
+f:
+        nop
+
+	.section	.text,"ax",@progbits,unique
+        .globl	g
+g:
+        nop
+
+// test that f and g are in different sections.
+
+// CHECK: .section	.text,"ax",@progbits,unique
+// CHECK: f:
+
+// CHECK: .section	.text,"ax",@progbits,unique
+// CHECK: g:
+
+// OBJ: Symbol {
+// OBJ:   Name:    f
+// OBJ:   Value:   0x0
+// OBJ:   Size:    0
+// OBJ:   Binding: Global
+// OBJ:   Type:    None
+// OBJ:   Other:   0
+// OBJ:   Section: .text (0x4)
+// OBJ: }
+// OBJ: Symbol {
+// OBJ:   Name:    g
+// OBJ:   Value:   0x0
+// OBJ:   Size:    0
+// OBJ:   Binding: Global
+// OBJ:   Type:    None
+// OBJ:   Other:   0
+// OBJ:   Section: .text (0x5)
+// OBJ: }