[MachO] Emit Weak ReadOnlyWithRel to ConstDataSection

[steven_wu]

Summary

Darwin dynamic linker can handle weak symbols in ConstDataSection.
ReadonReadOnlyWithRel symbols should be emitted in ConstDataSection
instead of normal DataSection.

rdar://problem/39298457

[dexonsmith]

Have you confirmed this doesn't need to depend on the deployment target? I.e., do we need the old logic sometimes when back-deploying?

Otherwise LGTM.

[kledzik]

LGTM

llvm/trunk/include/llvm/MC/MCObjectFileInfo.h

protected:
   const MCSection *TLSThreadInitSection; // Defaults to ".thread_init_func".
 
   MCSection *CStringSection;
   MCSection *UStringSection;
   MCSection *TextCoalSection;
   MCSection *ConstTextCoalSection;
   MCSection *ConstDataSection;
   MCSection *DataCoalSection;
+  MCSection *ConstDataCoalSection;
   MCSection *DataCommonSection;
   MCSection *DataBSSSection;
   MCSection *FourByteConstantSection;
   MCSection *EightByteConstantSection;
   MCSection *SixteenByteConstantSection;
   MCSection *LazySymbolPointerSection;
   MCSection *NonLazySymbolPointerSection;
   MCSection *ThreadLocalPointerSection;
public:
   const MCSection *getCStringSection() const { return CStringSection; }
   const MCSection *getUStringSection() const { return UStringSection; }
   MCSection *getTextCoalSection() const { return TextCoalSection; }
   const MCSection *getConstTextCoalSection() const {
     return ConstTextCoalSection;
   }
   const MCSection *getConstDataSection() const { return ConstDataSection; }
   const MCSection *getDataCoalSection() const { return DataCoalSection; }
+  const MCSection *getConstDataCoalSection() const {
+    return ConstDataCoalSection;
+  }
   const MCSection *getDataCommonSection() const { return DataCommonSection; }
   MCSection *getDataBSSSection() const { return DataBSSSection; }
   const MCSection *getFourByteConstantSection() const {
     return FourByteConstantSection;
   }
   const MCSection *getEightByteConstantSection() const {
     return EightByteConstantSection;
   }

llvm/trunk/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
   if (Kind.isText())
     return GO->isWeakForLinker() ? TextCoalSection : TextSection;
 
   // If this is weak/linkonce, put this in a coalescable section, either in text
   // or data depending on if it is writable.
   if (GO->isWeakForLinker()) {
     if (Kind.isReadOnly())
       return ConstTextCoalSection;
+    if (Kind.isReadOnlyWithRel())
+      return ConstDataCoalSection;
     return DataCoalSection;
   }
 
   // FIXME: Alignment check should be handled by section classifier.
   if (Kind.isMergeable1ByteCString() &&
       GO->getParent()->getDataLayout().getPreferredAlignment(
           cast<GlobalVariable>(GO)) < 32)
     return CStringSection;

llvm/trunk/lib/MC/MCObjectFileInfo.cpp

void MCObjectFileInfo::initMachOMCObjectFileInfo(const Triple &T) {
   // If the target is not powerpc, map the coal sections to the non-coal
   // sections.
   //
   // "__TEXT/__textcoal_nt" => section "__TEXT/__text"
   // "__TEXT/__const_coal"  => section "__TEXT/__const"
   // "__DATA/__datacoal_nt" => section "__DATA/__data"
   Triple::ArchType ArchTy = T.getArch();
 
+  ConstDataSection  // .const_data
+    = Ctx->getMachOSection("__DATA", "__const", 0,
+                           SectionKind::getReadOnlyWithRel());
+
   if (ArchTy == Triple::ppc || ArchTy == Triple::ppc64) {
     TextCoalSection
       = Ctx->getMachOSection("__TEXT", "__textcoal_nt",
                              MachO::S_COALESCED |
                              MachO::S_ATTR_PURE_INSTRUCTIONS,
                              SectionKind::getText());
     ConstTextCoalSection
       = Ctx->getMachOSection("__TEXT", "__const_coal",
                              MachO::S_COALESCED,
                              SectionKind::getReadOnly());
     DataCoalSection = Ctx->getMachOSection(
         "__DATA", "__datacoal_nt", MachO::S_COALESCED, SectionKind::getData());
+    ConstDataCoalSection = DataCoalSection;
   } else {
     TextCoalSection = TextSection;
     ConstTextCoalSection = ReadOnlySection;
     DataCoalSection = DataSection;
+    ConstDataCoalSection = ConstDataSection;
   }
 
-  ConstDataSection  // .const_data
-    = Ctx->getMachOSection("__DATA", "__const", 0,
-                           SectionKind::getReadOnlyWithRel());
   DataCommonSection
     = Ctx->getMachOSection("__DATA","__common",
                            MachO::S_ZEROFILL,
                            SectionKind::getBSS());
   DataBSSSection
     = Ctx->getMachOSection("__DATA","__bss", MachO::S_ZEROFILL,
                            SectionKind::getBSS());
 

llvm/trunk/test/CodeGen/X86/global-sections.ll

 ; LINUX-SECTIONS: .type G17,@object
 ; LINUX-SECTIONS: .section  .bss.G17,"aw",@nobits
 ; LINUX-SECTIONS: .byte 0
 ; LINUX-SECTIONS: .size G17, 1
 
 ; WIN32-SECTIONS: .section  .bss,"bw",one_only,_G17
 ; WIN32-SECTIONS: _G17:
 ; WIN32-SECTIONS:.byte  0
+
+; check weak ReadOnlyWithRel globals.
+@G18 = linkonce_odr unnamed_addr constant i64* @G15
+; DARWIN64: .section      __DATA,__const
+; DARWIN64: _G18: