[AIX] emit .extern and .weak directive linkage

SUMMARY:

emit .extern and .weak directive linkage

Reviewers: hubert.reinterpretcast, Jason Liu
Subscribers: wuzish, nemanjai, hiraditya

Differential Revision: https://reviews.llvm.org/D76932

Author: diggerlin

llvm/include/llvm/MC/MCAsmInfo.h

@@ -307,6 +307,10 @@ class MCAsmInfo {
   /// false.
   bool HasAltEntry = false;
 
+  /// True if this target supports the XCOFF .extern directive.  Defaults to
+  /// false.
+  bool HasDotExternDirective = false;
+
   /// Used to declare a global as being a weak symbol. Defaults to ".weak".
   const char *WeakDirective;
 
@@ -583,6 +587,7 @@ class MCAsmInfo {
   bool hasIdentDirective() const { return HasIdentDirective; }
   bool hasNoDeadStrip() const { return HasNoDeadStrip; }
   bool hasAltEntry() const { return HasAltEntry; }
+  bool hasDotExternDirective() const { return HasDotExternDirective; }
   const char *getWeakDirective() const { return WeakDirective; }
   const char *getWeakRefDirective() const { return WeakRefDirective; }
   bool hasWeakDefDirective() const { return HasWeakDefDirective; }

llvm/include/llvm/MC/MCDirectives.h

@@ -29,6 +29,7 @@ enum MCSymbolAttr {
   MCSA_ELF_TypeGnuUniqueObject, /// .type _foo, @gnu_unique_object
   MCSA_Global,                  ///< .globl
   MCSA_LGlobal,                 ///< .lglobl (XCOFF)
+  MCSA_Extern,                  ///< .extern (XCOFF)
   MCSA_Hidden,                  ///< .hidden (ELF)
   MCSA_IndirectSymbol,          ///< .indirect_symbol (MachO)
   MCSA_Internal,                ///< .internal (ELF)

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -395,6 +395,8 @@ void AsmPrinter::emitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const {
   GlobalValue::LinkageTypes Linkage = GV->getLinkage();
   switch (Linkage) {
   case GlobalValue::CommonLinkage:
+    assert(!TM.getTargetTriple().isOSBinFormatXCOFF() &&
+           "CommonLinkage of XCOFF should not come to this path.");
   case GlobalValue::LinkOnceAnyLinkage:
   case GlobalValue::LinkOnceODRLinkage:
   case GlobalValue::WeakAnyLinkage:
@@ -418,18 +420,25 @@ void AsmPrinter::emitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const {
     }
     return;
   case GlobalValue::ExternalLinkage:
-    // If external, declare as a global symbol: .globl _foo
-    OutStreamer->emitSymbolAttribute(GVSym, MCSA_Global);
+    if (MAI->hasDotExternDirective() && GV->isDeclaration())
+      OutStreamer->emitSymbolAttribute(GVSym, MCSA_Extern);
+    else
+      OutStreamer->emitSymbolAttribute(GVSym, MCSA_Global);
     return;
   case GlobalValue::PrivateLinkage:
     return;
   case GlobalValue::InternalLinkage:
     if (MAI->hasDotLGloblDirective())
       OutStreamer->emitSymbolAttribute(GVSym, MCSA_LGlobal);
     return;
+  case GlobalValue::ExternalWeakLinkage:
+    if (TM.getTargetTriple().isOSBinFormatXCOFF()) {
+      OutStreamer->emitSymbolAttribute(GVSym, MCSA_Weak);
+      return;
+    }
+    LLVM_FALLTHROUGH;
   case GlobalValue::AppendingLinkage:
   case GlobalValue::AvailableExternallyLinkage:
-  case GlobalValue::ExternalWeakLinkage:
     llvm_unreachable("Should never emit this");
   }
   llvm_unreachable("Unknown linkage type!");
@@ -1489,15 +1498,30 @@ bool AsmPrinter::doFinalization(Module &M) {
   // Emit remaining GOT equivalent globals.
   emitGlobalGOTEquivs();
 
-  // Emit visibility info for declarations
+  // Emit linkage(XCOFF) and visibility info for declarations
   for (const Function &F : M) {
     if (!F.isDeclarationForLinker())
       continue;
+
+    MCSymbol *Name = getSymbol(&F);
+    // Function getSymbol gives us the function descriptor symbol for XCOFF.
+    if (TM.getTargetTriple().isOSBinFormatXCOFF() && !F.isIntrinsic()) {
+
+      // Get the function entry point symbol.
+      MCSymbol *FnEntryPointSym = OutContext.getOrCreateSymbol(
+          "." + cast<MCSymbolXCOFF>(Name)->getUnqualifiedName());
+      if (cast<MCSymbolXCOFF>(FnEntryPointSym)->hasRepresentedCsectSet())
+        // Emit linkage for the function entry point.
+        emitLinkage(&F, FnEntryPointSym);
+
+      // Emit linkage for the function descriptor.
+      emitLinkage(&F, Name);
+    }
+
     GlobalValue::VisibilityTypes V = F.getVisibility();
     if (V == GlobalValue::DefaultVisibility)
       continue;
 
-    MCSymbol *Name = getSymbol(&F);
     emitVisibility(Name, V, false);
   }
 

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -2131,15 +2131,19 @@ XCOFF::StorageClass TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(
   case GlobalValue::CommonLinkage:
     return XCOFF::C_EXT;
   case GlobalValue::ExternalWeakLinkage:
+  case GlobalValue::LinkOnceAnyLinkage:
   case GlobalValue::LinkOnceODRLinkage:
+  case GlobalValue::WeakAnyLinkage:
+  case GlobalValue::WeakODRLinkage:
     return XCOFF::C_WEAKEXT;
   case GlobalValue::AppendingLinkage:
     report_fatal_error(
         "There is no mapping that implements AppendingLinkage for XCOFF.");
-  default:
-    report_fatal_error(
-        "Unhandled linkage when mapping linkage to StorageClass.");
+  case GlobalValue::AvailableExternallyLinkage:
+    report_fatal_error("unhandled AvailableExternallyLinkage when mapping "
+                       "linkage to StorageClass");
   }
+  llvm_unreachable("Unknown linkage type!");
 }
 
 MCSection *TargetLoweringObjectFileXCOFF::getSectionForFunctionDescriptor(

llvm/lib/MC/MCAsmInfoXCOFF.cpp

@@ -15,6 +15,7 @@ void MCAsmInfoXCOFF::anchor() {}
 MCAsmInfoXCOFF::MCAsmInfoXCOFF() {
   IsLittleEndian = false;
   HasDotTypeDotSizeDirective = false;
+  HasDotExternDirective = true;
   COMMDirectiveAlignmentIsInBytes = false;
   LCOMMDirectiveAlignmentType = LCOMM::Log2Alignment;
   UseDotAlignForAlignment = true;

llvm/lib/MC/MCAsmStreamer.cpp

@@ -675,6 +675,9 @@ bool MCAsmStreamer::emitSymbolAttribute(MCSymbol *Symbol,
     break;
   case MCSA_Protected:      OS << "\t.protected\t";       break;
   case MCSA_Reference:      OS << "\t.reference\t";       break;
+  case MCSA_Extern:
+    OS << "\t.extern\t";
+    break;
   case MCSA_Weak:           OS << MAI->getWeakDirective(); break;
   case MCSA_WeakDefinition:
     OS << "\t.weak_definition\t";

llvm/lib/MC/MCXCOFFStreamer.cpp

@@ -35,13 +35,18 @@ bool MCXCOFFStreamer::emitSymbolAttribute(MCSymbol *Sym,
 
   switch (Attribute) {
   case MCSA_Global:
+  case MCSA_Extern:
     Symbol->setStorageClass(XCOFF::C_EXT);
     Symbol->setExternal(true);
     break;
   case MCSA_LGlobal:
     Symbol->setStorageClass(XCOFF::C_HIDEXT);
     Symbol->setExternal(true);
     break;
+  case llvm::MCSA_Weak:
+    Symbol->setStorageClass(XCOFF::C_WEAKEXT);
+    Symbol->setExternal(true);
+    break;
   default:
     report_fatal_error("Not implemented yet.");
   }

llvm/lib/MC/XCOFFObjectWriter.cpp

@@ -354,21 +354,24 @@ void XCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
       // Handle undefined symbol.
       UndefinedCsects.emplace_back(ContainingCsect);
       SectionMap[ContainingCsect] = &UndefinedCsects.back();
-    } else {
-      // If the symbol is the csect itself, we don't need to put the symbol
-      // into csect's Syms.
-      if (XSym == ContainingCsect->getQualNameSymbol())
-        continue;
+      if (nameShouldBeInStringTable(ContainingCsect->getName()))
+        Strings.add(ContainingCsect->getName());
+      continue;
+    }
 
-      // Only put a label into the symbol table when it is an external label.
-      if (!XSym->isExternal())
-        continue;
+    // If the symbol is the csect itself, we don't need to put the symbol
+    // into csect's Syms.
+    if (XSym == ContainingCsect->getQualNameSymbol())
+      continue;
 
-      assert(SectionMap.find(ContainingCsect) != SectionMap.end() &&
-             "Expected containing csect to exist in map");
-      // Lookup the containing csect and add the symbol to it.
-      SectionMap[ContainingCsect]->Syms.emplace_back(XSym);
-    }
+    // Only put a label into the symbol table when it is an external label.
+    if (!XSym->isExternal())
+      continue;
+
+    assert(SectionMap.find(ContainingCsect) != SectionMap.end() &&
+           "Expected containing csect to exist in map");
+    // Lookup the containing csect and add the symbol to it.
+    SectionMap[ContainingCsect]->Syms.emplace_back(XSym);
 
     // If the name does not fit in the storage provided in the symbol table
     // entry, add it to the string table.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -1616,9 +1616,10 @@ void PPCAIXAsmPrinter::emitGlobalVariable(const GlobalVariable *GV) {
   GVSym->setStorageClass(
       TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(GV));
 
-  // External global variables are already handled.
-  if (GV->isDeclaration())
+  if (GV->isDeclarationForLinker()) {
+    emitLinkage(GV, GVSym);
     return;
+  }
 
   SectionKind GVKind = getObjFileLowering().getKindForGlobal(GV, TM);
   if (!GVKind.isGlobalWriteableData() && !GVKind.isReadOnly())

llvm/test/CodeGen/PowerPC/aix-LinkOnceAnyLinkage.ll

@@ -0,0 +1,13 @@
+; RUN: llc -mtriple powerpc-ibm-aix-xcoff < %s | \
+; RUN: FileCheck %s
+
+; RUN: llc -mtriple powerpc64-ibm-aix-xcoff < %s | \
+; RUN: FileCheck %s
+
+define linkonce void @_Z3fooIiEvT_() {
+entry:
+  ret void
+}
+
+; CHECK: .weak   _Z3fooIiEvT_[DS]
+; CHECK: .weak   ._Z3fooIiEvT_

llvm/test/CodeGen/PowerPC/aix-LinkOnceODRLinkage.ll

@@ -9,5 +9,5 @@ entry:
   ret void
 }
 
-; CHECK: .weak   _Z3fooIiEvT_
+; CHECK: .weak   _Z3fooIiEvT_[DS]
 ; CHECK: .weak   ._Z3fooIiEvT_

llvm/test/CodeGen/PowerPC/aix-WeakODRLinkage.ll

@@ -0,0 +1,13 @@
+; RUN: llc -mtriple powerpc-ibm-aix-xcoff < %s | \
+; RUN: FileCheck %s
+
+; RUN: llc -mtriple powerpc64-ibm-aix-xcoff < %s | \
+; RUN: FileCheck %s
+
+define weak_odr void @_Z3fooIiEvT_() {
+entry:
+  ret void
+}
+
+; CHECK: .weak   _Z3fooIiEvT_[DS]
+; CHECK: .weak   ._Z3fooIiEvT_