[AIX] Add a TargetLoweringObjectFile for XCOFF and add support for common variables.

[sfertile]

Summary

Stubs out a TargetLoweringObjectFileXCOFF class, implementing only SelectSectionForGlobal for common symbols. Also adds an override of EmitGlobalVariable in PPCAIXAsmPrinter which adds a number of defensive errors and adds support for emitting common globals.

[daltenty]

LGTM

[sfertile]

Committed in https://reviews.llvm.org/rG942537d9fa50

[hubert.reinterpretcast]

llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

223

Please place these in order:
Initialize
shouldPutJumpTableInFunctionSection
getExplicitSectionGlobal
getStaticCtorSection
getStaticDtorSection
lowerRelativeReference
SelectSectionForGlobal

llvm/include/llvm/MC/MCSectionXCOFF.h

26

The common should indicate its scope as applying only to the current state of the implementation in LLVM (and not as a general statement on XCOFF).

43

Suggestion: Invalid or unhandled type for csect.

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

1819

report_fatal_error.

1841

report_fatal_error.

1854

report_fatal_error.

1859

report_fatal_error.

1865

report_fatal_error.

llvm/lib/MC/MCSectionXCOFF.cpp

23

Is the ".text" here meant to be the XCOFF section name? If so, then the comment on line 33 could say ".bss" instead of "common" to be consistent.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

1659

This is true for the OS and not just LLVM: s/on/by/.

1663

Add "for now".

1666

Use cast unless if we are expecting the cast to possibly fail and passing NULL to SwitchSection is okay.

1671

See comment above.

1672

llvm::DataLayout has a non-trivial destructor. I advise against copying.

llvm/test/CodeGen/PowerPC/aix-xcoff-common.ll

9

What is the intended difference between "d" and "comm"?

[sfertile]

@hubert.reinterpretcast I've committed a patch that addresses your comments: https://reviews.llvm.org/rL367324.

llvm/include/llvm/BinaryFormat/XCOFF.h

enum StorageClass : uint8_t {
   C_ALIAS = 105,  // Duplicate tag
   C_HIDDEN = 106, // Special storage class for external
   C_EFCN = 255,   // Physical end of function
 
   // Storage classes - reserved
   C_TCSYM = 134 // Reserved
 };
 
+enum SymbolType {
+  XTY_ER = 0, ///< External reference.
+  XTY_SD = 1, ///< Csect definition for initialized storage.
+  XTY_LD = 2, ///< Label definition.
+              ///< Defines an entry point to an initialized csect.
+  XTY_CM = 3  ///< Common csect definition. For uninitialized storage.
+};
+
 } // end namespace XCOFF
 } // end namespace llvm
 
 #endif

llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

public:
   MCSection *getStaticDtorSection(unsigned Priority,
                                   const MCSymbol *KeySym) const override;
 
   const MCExpr *lowerRelativeReference(const GlobalValue *LHS,
                                        const GlobalValue *RHS,
                                        const TargetMachine &TM) const override;
 };
 
+class TargetLoweringObjectFileXCOFF : public TargetLoweringObjectFile {
+public:
+  TargetLoweringObjectFileXCOFF() = default;
+  ~TargetLoweringObjectFileXCOFF() override = default;
+
+  MCSection *getExplicitSectionGlobal(const GlobalObject *GO, SectionKind Kind,
+                                      const TargetMachine &TM) const override;
+
+  MCSection *SelectSectionForGlobal(const GlobalObject *GO, SectionKind Kind,
+                                    const TargetMachine &TM) const override;
+
+  bool shouldPutJumpTableInFunctionSection(bool UsesLabelDifference,
+                                           const Function &F) const override;
+
+  void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
+
+  MCSection *getStaticCtorSection(unsigned Priority,
+                                  const MCSymbol *KeySym) const override;
+  MCSection *getStaticDtorSection(unsigned Priority,
+                                  const MCSymbol *KeySym) const override;
+
+  const MCExpr *lowerRelativeReference(const GlobalValue *LHS,
+                                       const GlobalValue *RHS,
+                                       const TargetMachine &TM) const override;
+};
+
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_TARGETLOWERINGOBJECTFILEIMPL_H

llvm/include/llvm/MC/MCContext.h

MCSectionWasm *getWasmSection(const Twine &Section, SectionKind K,
                                   const char *BeginSymName);
 
     MCSectionWasm *getWasmSection(const Twine &Section, SectionKind K,
                                   const MCSymbolWasm *Group, unsigned UniqueID,
                                   const char *BeginSymName);
 
     MCSectionXCOFF *getXCOFFSection(StringRef Section,
                                     XCOFF::StorageMappingClass MappingClass,
-                                    SectionKind K,
+                                    XCOFF::SymbolType CSectType, SectionKind K,
                                     const char *BeginSymName = nullptr);
 
     // Create and save a copy of STI and return a reference to the copy.
     MCSubtargetInfo &getSubtargetCopy(const MCSubtargetInfo &STI);
 
     /// @}
 
     /// \name Dwarf Management

llvm/include/llvm/MC/MCSectionXCOFF.h

 #include "llvm/MC/MCSection.h"
 
 namespace llvm {
 
 class MCSymbol;
 
 // This class represents an XCOFF `Control Section`, more commonly referred to
 // as a csect. A csect represents the smallest possible unit of data/code which
-// will be relocated as a single block.
+// will be relocated as a single block. A csect can either be:
+// 1) Initialized: The Type will be XTY_SD, and the symbols inside the csect
+//    will have a label definition representing their offset within the csect.
+// 2) Uninitialized: The Type will be XTY_CM, it will contain a single symbol,
+//    and may not contain label definitions.
 class MCSectionXCOFF final : public MCSection {
   friend class MCContext;
 
   StringRef Name;
   XCOFF::StorageMappingClass MappingClass;
+  XCOFF::SymbolType Type;
 
   MCSectionXCOFF(StringRef Section, XCOFF::StorageMappingClass SMC,
-                 SectionKind K, MCSymbol *Begin)
-      : MCSection(SV_XCOFF, K, Begin), Name(Section), MappingClass(SMC) {}
+                 XCOFF::SymbolType ST, SectionKind K, MCSymbol *Begin)
+      : MCSection(SV_XCOFF, K, Begin), Name(Section), MappingClass(SMC),
+        Type(ST) {
+    assert((ST == XCOFF::XTY_SD || ST == XCOFF::XTY_CM) &&
+           "Unexpected type for csect.");
+  }
 
 public:
   ~MCSectionXCOFF();
 
   static bool classof(const MCSection *S) {
     return S->getVariant() == SV_XCOFF;
   }
 
   StringRef getSectionName() const { return Name; }
   XCOFF::StorageMappingClass getMappingClass() const { return MappingClass; }
+  XCOFF::SymbolType getCSectType() const { return Type; }
 
   void PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
                             raw_ostream &OS,
                             const MCExpr *Subsection) const override;
   bool UseCodeAlign() const override;
   bool isVirtualSection() const override;
 };
 
 } // end namespace llvm
 
 #endif

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

 #include "llvm/IR/Type.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCSectionWasm.h"
+#include "llvm/MC/MCSectionXCOFF.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/MC/SectionKind.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CodeGen.h"
return Priority == UINT16_MAX ?
                                      SectionKind::getData());
 }
 
 MCSection *TargetLoweringObjectFileWasm::getStaticDtorSection(
     unsigned Priority, const MCSymbol *KeySym) const {
   llvm_unreachable("@llvm.global_dtors should have been lowered already");
   return nullptr;
 }
+
+//===----------------------------------------------------------------------===//
+//                                  XCOFF
+//===----------------------------------------------------------------------===//
+MCSection *TargetLoweringObjectFileXCOFF::getExplicitSectionGlobal(
+    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
+  llvm_unreachable("XCOFF explicit sections not yet implemented.");
+}
+
+MCSection *TargetLoweringObjectFileXCOFF::SelectSectionForGlobal(
+    const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
+  assert(!TM.getFunctionSections() && !TM.getDataSections() &&
+         "XCOFF unique sections not yet implemented.");
+
+  // Common symbols go into a csect with matching name which will get mapped
+  // into the .bss section.
+  if (Kind.isCommon()) {
+    SmallString<128> Name;
+    getNameWithPrefix(Name, GO, TM);
+    return getContext().getXCOFFSection(Name, XCOFF::XMC_RW, XCOFF::XTY_CM,
+                                        Kind, /* BeginSymbolName */ nullptr);
+  }
+
+  report_fatal_error("XCOFF other section types not yet implemented.");
+}
+
+bool TargetLoweringObjectFileXCOFF::shouldPutJumpTableInFunctionSection(
+    bool UsesLabelDifference, const Function &F) const {
+  llvm_unreachable("TLOF XCOFF not yet implemented.");
+}
+
+void TargetLoweringObjectFileXCOFF::Initialize(MCContext &Ctx,
+                                               const TargetMachine &TgtM) {
+  TargetLoweringObjectFile::Initialize(Ctx, TgtM);
+  TTypeEncoding = 0;
+  PersonalityEncoding = 0;
+  LSDAEncoding = 0;
+}
+
+MCSection *TargetLoweringObjectFileXCOFF::getStaticCtorSection(
+    unsigned Priority, const MCSymbol *KeySym) const {
+  llvm_unreachable("XCOFF ctor section not yet implemented.");
+}
+
+MCSection *TargetLoweringObjectFileXCOFF::getStaticDtorSection(
+    unsigned Priority, const MCSymbol *KeySym) const {
+  llvm_unreachable("XCOFF dtor section not yet implemented.");
+}
+
+const MCExpr *TargetLoweringObjectFileXCOFF::lowerRelativeReference(
+    const GlobalValue *LHS, const GlobalValue *RHS,
+    const TargetMachine &TM) const {
+  llvm_unreachable("XCOFF not yet implemented.");
+}

llvm/lib/MC/MCAsmInfoXCOFF.cpp

 
 using namespace llvm;
 
 void MCAsmInfoXCOFF::anchor() {}
 
 MCAsmInfoXCOFF::MCAsmInfoXCOFF() {
   IsLittleEndian = false;
   HasDotTypeDotSizeDirective = false;
+  COMMDirectiveAlignmentIsInBytes = false;
 }

llvm/lib/MC/MCContext.cpp

MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind Kind,
   F->setParent(Result);
   Begin->setFragment(F);
 
   return Result;
 }
 
 MCSectionXCOFF *MCContext::getXCOFFSection(StringRef Section,
                                            XCOFF::StorageMappingClass SMC,
+                                           XCOFF::SymbolType Type,
                                            SectionKind Kind,
                                            const char *BeginSymName) {
   // Do the lookup. If we have a hit, return it.
   auto IterBool = XCOFFUniquingMap.insert(
       std::make_pair(XCOFFSectionKey{Section.str(), SMC}, nullptr));
   auto &Entry = *IterBool.first;
   if (!IterBool.second)
     return Entry.second;
 
   // Otherwise, return a new section.
   StringRef CachedName = Entry.first.SectionName;
 
   MCSymbol *Begin = nullptr;
   if (BeginSymName)
     Begin = createTempSymbol(BeginSymName, false);
 
   MCSectionXCOFF *Result = new (XCOFFAllocator.Allocate())
-      MCSectionXCOFF(CachedName, SMC, Kind, Begin);
+      MCSectionXCOFF(CachedName, SMC, Type, Kind, Begin);
   Entry.second = Result;
 
   auto *F = new MCDataFragment();
   Result->getFragmentList().insert(Result->begin(), F);
   F->setParent(Result);
 
   if (Begin)
     Begin->setFragment(F);

llvm/lib/MC/MCObjectFileInfo.cpp

void MCObjectFileInfo::initWasmMCObjectFileInfo(const Triple &T) {
   // TODO: Define more sections.
 }
 
 void MCObjectFileInfo::initXCOFFMCObjectFileInfo(const Triple &T) {
   // The default csect for program code. Functions without a specified section
   // get placed into this csect. The choice of csect name is not a property of
   // the ABI or object file format. For example, the XL compiler uses an unnamed
   // csect for program code.
-  TextSection = Ctx->getXCOFFSection(
-      ".text", XCOFF::StorageMappingClass::XMC_PR, SectionKind::getText());
+  TextSection =
+      Ctx->getXCOFFSection(".text", XCOFF::StorageMappingClass::XMC_PR,
+                           XCOFF::XTY_SD, SectionKind::getText());
 }
 
 void MCObjectFileInfo::InitMCObjectFileInfo(const Triple &TheTriple, bool PIC,
                                             MCContext &ctx,
                                             bool LargeCodeModel) {
   PositionIndependent = PIC;
   Ctx = &ctx;
 

llvm/lib/MC/MCSectionXCOFF.cpp

 using namespace llvm;
 
 MCSectionXCOFF::~MCSectionXCOFF() = default;
 
 void MCSectionXCOFF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
                                           raw_ostream &OS,
                                           const MCExpr *Subsection) const {
   if (getKind().isText()) {
+    if (getMappingClass() != XCOFF::XMC_PR)
+      llvm_unreachable("Unsupported storage-mapping class for .text csect");
+
     OS << "\t.csect " << getSectionName() << "["
        << "PR"
        << "]" << '\n';
     return;
   }
 
+  if (getKind().isCommon()) {
+    if (getMappingClass() != XCOFF::XMC_RW)
+      llvm_unreachable("Unsupported storage-mapping class for common csect");
+    if (getCSectType() != XCOFF::XTY_CM)
+      llvm_unreachable("wrong csect type for common csect");
+    // Don't have to print a directive for switching to section for commons.
+    // '.comm' and '.lcomm' directives for the variable will create the needed
+    // csect.
+    return;
+  }
+
   report_fatal_error("Printing for this SectionKind is unimplemented.");
 }
 
 bool MCSectionXCOFF::UseCodeAlign() const { return getKind().isText(); }
 
-bool MCSectionXCOFF::isVirtualSection() const { return !getKind().isCommon(); }
+bool MCSectionXCOFF::isVirtualSection() const { return XCOFF::XTY_CM == Type; }

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

 #include "llvm/IR/Module.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstBuilder.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCSectionXCOFF.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCSymbolELF.h"
+#include "llvm/MC/MCSymbolXCOFF.h"
 #include "llvm/MC/SectionKind.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"

 };
 
 class PPCAIXAsmPrinter : public PPCAsmPrinter {
 public:
   PPCAIXAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
       : PPCAsmPrinter(TM, std::move(Streamer)) {}
 
   StringRef getPassName() const override { return "AIX PPC Assembly Printer"; }
+
+  void EmitGlobalVariable(const GlobalVariable *GV) override;
 };
 
 } // end anonymous namespace
 
 void PPCAsmPrinter::PrintSymbolOperand(const MachineOperand &MO,
                                        raw_ostream &O) {
   // Computing the address of a global symbol, not calling it.
   const GlobalValue *GV = MO.getGlobal();
bool PPCDarwinAsmPrinter::doFinalization(Module &M) {
   // implementation of multiple entry points).  If this doesn't occur, the
   // linker can safely perform dead code stripping.  Since LLVM never generates
   // code that does this, it is always safe to set.
   OutStreamer->EmitAssemblerFlag(MCAF_SubsectionsViaSymbols);
 
   return AsmPrinter::doFinalization(M);
 }
 
+void PPCAIXAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
+  // Early error checking limiting what is supported.
+  if (GV->isThreadLocal())
+    report_fatal_error("Thread local not yet supported on AIX.");
+
+  if (GV->hasSection())
+    report_fatal_error("Custom section for Data not yet supported.");
+
+  if (GV->hasComdat())
+    report_fatal_error("COMDAT not yet supported on AIX.");
+
+  SectionKind GVKind = getObjFileLowering().getKindForGlobal(GV, TM);
+  if (!GVKind.isCommon())
+    report_fatal_error("Only common variables are supported on AIX.");
+
+  // Create the containing csect and switch to it.
+  MCSectionXCOFF *CSect = dyn_cast<MCSectionXCOFF>(
+      getObjFileLowering().SectionForGlobal(GV, GVKind, TM));
+  OutStreamer->SwitchSection(CSect);
+
+  // Create the symbol and emit it.
+  MCSymbolXCOFF *XSym = dyn_cast<MCSymbolXCOFF>(getSymbol(GV));
+  auto DL = GV->getParent()->getDataLayout();
+  unsigned Align =
+      GV->getAlignment() ? GV->getAlignment() : DL.getPreferredAlignment(GV);
+  uint64_t Size = DL.getTypeAllocSize(GV->getType()->getElementType());
+  OutStreamer->EmitCommonSymbol(XSym, Size, Align);
+}
+
 /// createPPCAsmPrinterPass - Returns a pass that prints the PPC assembly code
 /// for a MachineFunction to the given output stream, in a format that the
 /// Darwin assembler can deal with.
 ///
 static AsmPrinter *
 createPPCAsmPrinterPass(TargetMachine &tm,
                         std::unique_ptr<MCStreamer> &&Streamer) {
   if (tm.getTargetTriple().isMacOSX())

llvm/lib/Target/PowerPC/PPCTargetMachine.cpp

if (OL != CodeGenOpt::None) {
     else
       FullFS = "+invariant-function-descriptors";
   }
 
   return FullFS;
 }
 
 static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
-  // If it isn't a Mach-O file then it's going to be a linux ELF
-  // object file.
   if (TT.isOSDarwin())
     return llvm::make_unique<TargetLoweringObjectFileMachO>();
 
+  if (TT.isOSAIX())
+    return llvm::make_unique<TargetLoweringObjectFileXCOFF>();
+
   return llvm::make_unique<PPC64LinuxTargetObjectFile>();
 }
 
 static PPCTargetMachine::PPCABI computeTargetABI(const Triple &TT,
                                                  const TargetOptions &Options) {
   if (TT.isOSDarwin())
     report_fatal_error("Darwin is no longer supported for PowerPC");
   

llvm/test/CodeGen/PowerPC/aix-xcoff-common.ll

+; RUN: llc -mtriple powerpc-ibm-aix-xcoff < %s | FileCheck %s
+
+@a = common global i32 0, align 4
+@b = common global i64 0, align 8
+@c = common global i16 0, align 2
+
+@d = common local_unnamed_addr global double 0.000000e+00, align 8
+@f = common local_unnamed_addr global float 0.000000e+00, align 4
+@comm = common local_unnamed_addr global double 0.000000e+00, align 8
+
+@over_aligned = common local_unnamed_addr global double 0.000000e+00, align 32
+
+@array = common local_unnamed_addr global [32 x i8] zeroinitializer, align 1
+
+; CHECK:      .csect .text[PR]
+; CHECK-NEXT:  .file
+; CHECK-NEXT: .comm   a,4,2
+; CHECK-NEXT: .comm   b,8,3
+; CHECK-NEXT: .comm   c,2,1
+; CHECK-NEXT: .comm   d,8,3
+; CHECK-NEXT: .comm   f,4,2
+; CHECK-NEXT: .comm   comm,8,3
+; CHECK-NEXT: .comm   over_aligned,8,5
+; CHECK-NEXT: .comm   array,32,0