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>.

llvm-svn: 228980

5 files changed, 51 insertions, 23 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 4f46e37d39c..8aa66531b3d 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/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);
-    TM.getNameWithPrefix(Name, GV, Mang, true);
-
+    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(
-        Name.str(), getELFSectionType(Name.str(), Kind), Flags, 0, Group);
+    return getContext().getELFSection(Name, getELFSectionType(Name, Kind),
+                                      Flags, 0, Group, !UniqueSectionNames);
   }
 
   if (Kind.isText()) return TextSection;
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 5bddb09393f..b4948e659fb 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/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);
 }
 
diff --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index 35609893e28..721edd451ee 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/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);
-  Entry.second = Result;
+      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);
+      new (*this) MCSectionELF(".group", ELF::SHT_GROUP, 0,
+                               SectionKind::getReadOnly(), 4, nullptr, false);
   return Result;
 }
 
diff --git a/llvm/lib/MC/MCParser/ELFAsmParser.cpp b/llvm/lib/MC/MCParser/ELFAsmParser.cpp
index 21c65ce0b83..7a120a105d2 100644
--- a/llvm/lib/MC/MCParser/ELFAsmParser.cpp
+++ b/llvm/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 =
-      getContext().getELFSection(SectionName, Type, Flags, Size, GroupName);
+  const MCSection *ELFSection = getContext().getELFSection(
+      SectionName, Type, Flags, Size, GroupName, Unique);
   getStreamer().SwitchSection(ELFSection, Subsection);
 
   if (getContext().getGenDwarfForAssembly()) {
diff --git a/llvm/lib/MC/MCSectionELF.cpp b/llvm/lib/MC/MCSectionELF.cpp
index fb364c87a03..da3868273a7 100644
--- a/llvm/lib/MC/MCSectionELF.cpp
+++ b/llvm/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)