[AIX][PowerPC][PGO] Generate .ref for some PGO sections

[w2yehia]

Summary

For PGO on AIX, when we switch to the linux-style PGO variable access (via _start and _stop labels), we need the compiler to generate a .ref assembly for each of the three csects:

• __llvm_prf_data[RW]
• __llvm_prf_names[RO]
• __llvm_prf_vnds[RW]

We insert the .ref inside the __llvm_prf_cnts[RW] csect so that if it's live then the 3 csects are live.

For example, for a testcase with at least one function definition, when compiled with -fprofile-generate we should generate:

.csect __llvm_prf_cnts[RW],3
.ref __llvm_prf_data[RW]   <<============ needs to be inserted
.ref __llvm_prf_names[RO]  <<===========

the __llvm_prf_vnds is not always present, so we reference it only when it's present.

[w2yehia]

clang-format

[w2yehia]

@sfertile @daltenty ping

[w2yehia]

@sfertile @daltenty ping

[sfertile]

LGTM Wael. Sorry for taking so long to get to it.

llvm/include/llvm/MC/MCContext.h

public:
     MCSectionWasm *getWasmSection(const Twine &Section, SectionKind K,
                                   unsigned Flags, const Twine &Group,
                                   unsigned UniqueID, const char *BeginSymName);
 
     MCSectionWasm *getWasmSection(const Twine &Section, SectionKind K,
                                   unsigned Flags, const MCSymbolWasm *Group,
                                   unsigned UniqueID, const char *BeginSymName);
 
+    bool hasXCOFFSection(StringRef Section,
+                         XCOFF::CsectProperties CsectProp) const;
+
     MCSectionXCOFF *getXCOFFSection(
         StringRef Section, SectionKind K,
         Optional<XCOFF::CsectProperties> CsectProp = None,
         bool MultiSymbolsAllowed = false, const char *BeginSymName = nullptr,
         Optional<XCOFF::DwarfSectionSubtypeFlags> DwarfSubtypeFlags = None);
 
     // Create and save a copy of STI and return a reference to the copy.
     MCSubtargetInfo &getSubtargetCopy(const MCSubtargetInfo &STI);

llvm/include/llvm/MC/MCStreamer.h

public:
   /// undesirable name.
   ///
   /// \param Name - The name used internally in the assembly for references to
   /// the symbol.
   /// \param Rename - The value to which the Name parameter is
   /// changed at the end of assembly.
   virtual void emitXCOFFRenameDirective(const MCSymbol *Name, StringRef Rename);
 
+  /// Emit a XCOFF .ref directive which creates R_REF type entry in the
+  /// relocation table for one or more symbols.
+  ///
+  /// \param Sym - The symbol on the .ref directive.
+  virtual void emitXCOFFRefDirective(StringRef Sym);
+
   /// Emit an ELF .size directive.
   ///
   /// This corresponds to an assembler statement such as:
   ///  .size symbol, expression
   virtual void emitELFSize(MCSymbol *Symbol, const MCExpr *Value);
 
   /// Emit an ELF .symver directive.
   ///

llvm/include/llvm/MC/MCXCOFFStreamer.h

void emitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
                     SMLoc Loc = SMLoc()) override;
   void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &) override;
   void emitXCOFFLocalCommonSymbol(MCSymbol *LabelSym, uint64_t Size,
                                   MCSymbol *CsectSym,
                                   unsigned ByteAlign) override;
   void emitXCOFFSymbolLinkageWithVisibility(MCSymbol *Symbol,
                                             MCSymbolAttr Linkage,
                                             MCSymbolAttr Visibility) override;
+  void emitXCOFFRefDirective(StringRef Name) override {
+    report_fatal_error("emitXCOFFRefDirective is not implemented yet on object"
+                       "generation path");
+  }
   void emitXCOFFRenameDirective(const MCSymbol *Name,
                                 StringRef Rename) override {
     report_fatal_error("emitXCOFFRenameDirective is not implemented yet on "
                        "object generation path");
   }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_MC_MCXCOFFSTREAMER_H

llvm/lib/MC/MCAsmStreamer.cpp

void emitXCOFFLocalCommonSymbol(MCSymbol *LabelSym, uint64_t Size,
                                   MCSymbol *CsectSym,
                                   unsigned ByteAlign) override;
   void emitXCOFFSymbolLinkageWithVisibility(MCSymbol *Symbol,
                                             MCSymbolAttr Linakge,
                                             MCSymbolAttr Visibility) override;
   void emitXCOFFRenameDirective(const MCSymbol *Name,
                                 StringRef Rename) override;
 
+  void emitXCOFFRefDirective(StringRef Name) override;
+
   void emitELFSize(MCSymbol *Symbol, const MCExpr *Value) override;
   void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
 
   /// Emit a local common (.lcomm) symbol.
   ///
   /// @param Symbol - The common symbol to emit.
   /// @param Size - The size of the common symbol.
for (char C : Rename) {
     if (C == DQ)
       OS << DQ;
     OS << C;
   }
   OS << DQ;
   EmitEOL();
 }
 
+void MCAsmStreamer::emitXCOFFRefDirective(StringRef Name) {
+  OS << "\t.ref " << Name;
+  EmitEOL();
+}
+
 void MCAsmStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
   assert(MAI->hasDotTypeDotSizeDirective());
   OS << "\t.size\t";
   Symbol->print(OS, MAI);
   OS << ", ";
   Value->print(OS, MAI);
   EmitEOL();
 }

llvm/lib/MC/MCContext.cpp

MCSectionWasm *MCContext::getWasmSection(const Twine &Section, SectionKind Kind,
   auto *F = new MCDataFragment();
   Result->getFragmentList().insert(Result->begin(), F);
   F->setParent(Result);
   Begin->setFragment(F);
 
   return Result;
 }
 
+bool MCContext::hasXCOFFSection(StringRef Section,
+                                XCOFF::CsectProperties CsectProp) const {
+  return XCOFFUniquingMap.count(
+             XCOFFSectionKey(Section.str(), CsectProp.MappingClass)) != 0;
+}
+
 MCSectionXCOFF *MCContext::getXCOFFSection(
     StringRef Section, SectionKind Kind,
     Optional<XCOFF::CsectProperties> CsectProp, bool MultiSymbolsAllowed,
     const char *BeginSymName,
     Optional<XCOFF::DwarfSectionSubtypeFlags> DwarfSectionSubtypeFlags) {
   bool IsDwarfSec = DwarfSectionSubtypeFlags.hasValue();
   assert((IsDwarfSec != CsectProp.hasValue()) && "Invalid XCOFF section!");
 

llvm/lib/MC/MCStreamer.cpp

 }
 
 void MCStreamer::emitXCOFFRenameDirective(const MCSymbol *Name,
                                           StringRef Rename) {
   llvm_unreachable("emitXCOFFRenameDirective is only supported on "
                    "XCOFF targets");
 }
 
+void MCStreamer::emitXCOFFRefDirective(StringRef Name) {
+  llvm_unreachable("emitXCOFFRefDirective is only supported on XCOFF targets");
+}
+
 void MCStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {}
 void MCStreamer::emitELFSymverDirective(const MCSymbol *OriginalSym,
                                         StringRef Name, bool KeepOriginalSym) {}
 void MCStreamer::emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                        unsigned ByteAlignment) {}
 void MCStreamer::emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
                                 uint64_t Size, unsigned ByteAlignment) {}
 void MCStreamer::changeSection(MCSection *, const MCExpr *) {}

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

public:
   void emitGlobalVariable(const GlobalVariable *GV) override;
 
   void emitFunctionDescriptor() override;
 
   void emitFunctionEntryLabel() override;
 
   void emitFunctionBodyEnd() override;
 
+  void emitPGORefs();
+
   void emitEndOfAsmFile(Module &) override;
 
   void emitLinkage(const GlobalValue *GV, MCSymbol *GVSym) const override;
 
   void emitInstruction(const MachineInstr *MI) override;
 
   bool doFinalization(Module &M) override;
 
void PPCAIXAsmPrinter::emitFunctionEntryLabel() {
   // Emit aliasing label for function entry point label.
   llvm::for_each(
       GOAliasMap[&MF->getFunction()], [this](const GlobalAlias *Alias) {
         OutStreamer->emitLabel(
             getObjFileLowering().getFunctionEntryPointSymbol(Alias, TM));
       });
 }
 
+void PPCAIXAsmPrinter::emitPGORefs() {
+  if (OutContext.hasXCOFFSection(
+          "__llvm_prf_cnts",
+          XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD))) {
+    MCSection *CntsSection = OutContext.getXCOFFSection(
+        "__llvm_prf_cnts", SectionKind::getData(),
+        XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD),
+        /*MultiSymbolsAllowed*/ true);
+
+    OutStreamer->SwitchSection(CntsSection);
+    if (OutContext.hasXCOFFSection(
+            "__llvm_prf_data",
+            XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD)))
+      OutStreamer->emitXCOFFRefDirective("__llvm_prf_data[RW]");
+    if (OutContext.hasXCOFFSection(
+            "__llvm_prf_names",
+            XCOFF::CsectProperties(XCOFF::XMC_RO, XCOFF::XTY_SD)))
+      OutStreamer->emitXCOFFRefDirective("__llvm_prf_names[RO]");
+    if (OutContext.hasXCOFFSection(
+            "__llvm_prf_vnds",
+            XCOFF::CsectProperties(XCOFF::XMC_RW, XCOFF::XTY_SD)))
+      OutStreamer->emitXCOFFRefDirective("__llvm_prf_vnds[RW]");
+  }
+}
+
 void PPCAIXAsmPrinter::emitEndOfAsmFile(Module &M) {
   // If there are no functions and there are no toc-data definitions in this
   // module, we will never need to reference the TOC base.
   if (M.empty() && TOCDataGlobalVars.empty())
     return;
 
+  emitPGORefs();
+
   // Switch to section to emit TOC base.
   OutStreamer->SwitchSection(getObjFileLowering().getTOCBaseSection());
 
   PPCTargetStreamer *TS =
       static_cast<PPCTargetStreamer *>(OutStreamer->getTargetStreamer());
 
   for (auto &I : TOC) {
     MCSectionXCOFF *TCEntry;

llvm/test/CodeGen/PowerPC/pgo-ref-directive.ll

+; RUN: rm -rf %t && split-file %s %t
+
+; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mattr=-altivec -mtriple powerpc-ibm-aix-xcoff -xcoff-traceback-table=false < %t/no-ref.ll | FileCheck %s --check-prefixes=NOREF
+; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mattr=-altivec -mtriple powerpc-ibm-aix-xcoff -xcoff-traceback-table=false < %t/no-vnds.ll | FileCheck %s --check-prefixes=NOVNDS
+; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mattr=-altivec -mtriple powerpc-ibm-aix-xcoff -xcoff-traceback-table=false < %t/with-vnds.ll | FileCheck %s --check-prefixes=WITHVNDS
+
+
+;--- no-ref.ll
+; The absence of a __llvm_prf_cnts section should stop generating the .refs.
+;
+target datalayout = "E-m:a-p:32:32-i64:64-n32"
+target triple = "powerpc-ibm-aix7.2.0.0"
+
+@__profd_main = private global i64 zeroinitializer, section "__llvm_prf_data", align 8
+@__llvm_prf_nm = private constant [6 x i8] c"\04\00main", section "__llvm_prf_names", align 1
+
[e-mail] = appending global [2 x i8*]
+  [i8* bitcast (i64* @__profd_main to i8*),
+   i8* getelementptr inbounds ([6 x i8], [6 x i8]* @__llvm_prf_nm, i32 0, i32 0)], section "llvm.metadata"
+
+define i32 @main() #0 {
+entry:
+  ret i32 1
+}
+
+; NOREF-NOT:  .ref __llvm_prf_data
+; NOREF-NOT:  .ref __llvm_prf_names
+; NOREF-NOT:  .ref __llvm_prf_vnds
+
+;--- no-vnds.ll
+; This is the most common case. When -fprofile-generate is used and there exists executable code, we generate the __llvm_prf_cnts, __llvm_prf_data, and __llvm_prf_names sections.
+;
+target datalayout = "E-m:a-p:32:32-i64:64-n32"
+target triple = "powerpc-ibm-aix7.2.0.0"
+
+@__profc_main = private global [1 x i64] zeroinitializer, section "__llvm_prf_cnts", align 8
+@__profd_main = private global i64 zeroinitializer, section "__llvm_prf_data", align 8
+@__llvm_prf_nm = private constant [6 x i8] c"\04\00main", section "__llvm_prf_names", align 1
+
[e-mail] = appending global [3 x i8*]
+  [i8* bitcast ([1 x i64]* @__profc_main to i8*),
+   i8* bitcast (i64* @__profd_main to i8*),
+   i8* getelementptr inbounds ([6 x i8], [6 x i8]* @__llvm_prf_nm, i32 0, i32 0)], section "llvm.metadata"
+
+define i32 @main() #0 {
+entry:
+  ret i32 1
+}
+; There will be two __llvm_prf_cnts .csects, one to represent the actual csect 
+; that holds @__profc_main, and one generated to hold the .ref directives. In 
+; XCOFF, a csect can be defined in pieces, so this is is legal assembly.
+;
+; NOVNDS:      .csect __llvm_prf_cnts[RW],3
+; NOVNDS:      .csect __llvm_prf_cnts[RW],3
+; NOVNDS-NEXT: .ref __llvm_prf_data[RW]
+; NOVNDS-NEXT: .ref __llvm_prf_names[RO]
+; NOVNDS-NOT:  .ref __llvm_prf_vnds
+
+;--- with-vnds.ll
+; When value profiling is needed, the PGO instrumentation generates variables in the __llvm_prf_vnds section, so we generate a .ref for them too.
+;
+@__profc_main = private global [1 x i64] zeroinitializer, section "__llvm_prf_cnts", align 8
+@__profd_main = private global i64 zeroinitializer, section "__llvm_prf_data", align 8
+@__llvm_prf_nm = private constant [6 x i8] c"\04\00main", section "__llvm_prf_names", align 1
+@__llvm_prf_vnodes = private global [10 x { i64, i64, i8* }] zeroinitializer, section "__llvm_prf_vnds"
+
[e-mail] = appending global [4 x i8*]
+  [i8* bitcast ([1 x i64]* @__profc_main to i8*),
+   i8* bitcast (i64* @__profd_main to i8*),
+   i8* getelementptr inbounds ([6 x i8], [6 x i8]* @__llvm_prf_nm, i32 0, i32 0),
+   i8* bitcast ([10 x { i64, i64, i8* }]* @__llvm_prf_vnodes to i8*)], section "llvm.metadata"
+
+define i32 @main() #0 {
+entry:
+  ret i32 1
+}
+
+; WITHVNDS:      .csect __llvm_prf_cnts[RW],3
+; WITHVNDS:      .csect __llvm_prf_cnts[RW],3
+; WITHVNDS-NEXT: .ref __llvm_prf_data[RW]
+; WITHVNDS-NEXT: .ref __llvm_prf_names[RO]
+; WITHVNDS-NEXT: .ref __llvm_prf_vnds[RW]