COFF: Let globals with private linkage reside in their own section

Summary:
COFF COMDATs (for selection kinds other than 'select any') require at
least one non-section symbol in the symbol table.
Satisfy this by morally enhancing the linkage from private to internal.

Reviewers: rafael

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8374

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232539 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

@@ -147,6 +147,10 @@ public:
                            SectionKind Kind, Mangler &Mang,
                            const TargetMachine &TM) const override;
 
+  void getNameWithPrefix(SmallVectorImpl<char> &OutName, const GlobalValue *GV,
+                         bool CannotUsePrivateLabel, Mangler &Mang,
+                         const TargetMachine &TM) const override;
+
   const MCSection *
   getSectionForJumpTable(const Function &F, Mangler &Mang,
                          const TargetMachine &TM) const override;

include/llvm/Target/TargetLoweringObjectFile.h

@@ -101,6 +101,11 @@ public:
     return SectionForGlobal(GV, getKindForGlobal(GV, TM), Mang, TM);
   }
 
+  virtual void getNameWithPrefix(SmallVectorImpl<char> &OutName,
+                                 const GlobalValue *GV,
+                                 bool CannotUsePrivateLabel, Mangler &Mang,
+                                 const TargetMachine &TM) const;
+
   virtual const MCSection *
   getSectionForJumpTable(const Function &F, Mangler &Mang,
                          const TargetMachine &TM) const;

lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -927,6 +927,11 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
       StringRef COMDATSymName = Sym->getName();
       return getContext().getCOFFSection(Name, Characteristics, Kind,
                                          COMDATSymName, Selection);
+    } else {
+      SmallString<256> TmpData;
+      getNameWithPrefix(TmpData, GV, true, Mang, TM);
+      return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
+                                         Selection);
     }
   }
 
@@ -948,6 +953,25 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
   return DataSection;
 }
 
+void TargetLoweringObjectFileCOFF::getNameWithPrefix(
+    SmallVectorImpl<char> &OutName, const GlobalValue *GV,
+    bool CannotUsePrivateLabel, Mangler &Mang, const TargetMachine &TM) const {
+  if (GV->hasPrivateLinkage() &&
+      ((isa<Function>(GV) && TM.getFunctionSections()) ||
+       (isa<GlobalVariable>(GV) && TM.getDataSections()))) {
+    SmallString<256> Tmp;
+    Mang.getNameWithPrefix(Tmp, GV, /*CannotUsePrivateLabel=*/false);
+    if (Tmp.startswith(".L"))
+      OutName.append(Tmp.begin() + 2, Tmp.end());
+    else if (Tmp.startswith("L"))
+      OutName.append(Tmp.begin() + 1, Tmp.end());
+    else
+      OutName.append(Tmp.begin(), Tmp.end());
+    return;
+  }
+  Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
+}
+
 const MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
   // If the function can be removed, produce a unique section so that

lib/Target/TargetLoweringObjectFile.cpp

@@ -343,3 +343,9 @@ const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol
   // null return could mean 'no location' & we should just do that here.
   return MCSymbolRefExpr::Create(Sym, *Ctx);
 }
+
+void TargetLoweringObjectFile::getNameWithPrefix(
+    SmallVectorImpl<char> &OutName, const GlobalValue *GV,
+    bool CannotUsePrivateLabel, Mangler &Mang, const TargetMachine &TM) const {
+  Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
+}

lib/Target/TargetMachine.cpp

@@ -175,7 +175,7 @@ void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
   const TargetLoweringObjectFile *TLOF = getObjFileLowering();
   const MCSection *TheSection = TLOF->SectionForGlobal(GV, GVKind, Mang, *this);
   bool CannotUsePrivateLabel = !canUsePrivateLabel(*AsmInfo, *TheSection);
-  Mang.getNameWithPrefix(Name, GV, CannotUsePrivateLabel);
+  TLOF->getNameWithPrefix(Name, GV, CannotUsePrivateLabel, Mang, *this);
 }
 
 MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV, Mangler &Mang) const {

test/CodeGen/X86/global-sections.ll

@@ -275,8 +275,8 @@ bb7:
 ; LINUX-SECTIONS:        .asciz  "foo"
 ; LINUX-SECTIONS:        .size   .LG14, 4
 
-; WIN32-SECTIONS:        .section        .rdata,"dr"
+; WIN32-SECTIONS:        .section        .rdata,"dr",one_only,_G14
-; WIN32-SECTIONS: L_G14:
+; WIN32-SECTIONS: _G14:
 ; WIN32-SECTIONS:        .asciz  "foo"
 
 ; cannot be merged on MachO, but can on other formats.