[RISCV] Replace @plt/@gotpcrel in data directives with %pltpcrel %gotpcrel

lld/test/ELF/riscv-reloc-plt32.s

@@ -18,6 +18,6 @@
 .globl _start
 _start:
 .data
-  .word foo@PLT - .
-  .word foo@PLT - . + 1
-  .word foo@PLT - . - 1
+  .word %pltpcrel(foo)
+  .word %pltpcrel(foo + 1)
+  .word %pltpcrel(foo - 1)

lld/test/ELF/riscv-undefined-weak.s

@@ -97,4 +97,4 @@ branch:
 # PC-NOT:      .plt:
 # PLT:         .plt:
 
-.word target@plt - .
+.word %pltpcrel(target)

lld/test/ELF/riscv64-reloc-got32-pcrel.s

@@ -12,16 +12,16 @@ bar:
 
   .globl _start
 _start:  // PC = 0x33a8
-// bar@GOTPCREL   = 0x2398 (got entry for `bar`) - 0x33a8 (.) = 0xf0efffff
-// bar@GOTPCREL+4 = 0x2398 (got entry for `bar`) - 0x33ac (.) + 4 = 0xf0efffff
-// bar@GOTPCREL-4 = 0x2398 (got entry for `bar`) - 0x33b0 (.) - 4 = 0xe4efffff
+// %gotpcrel(bar)   = 0x2398 (got entry for `bar`) - 0x33a8 (.) = 0xf0efffff
+// %gotpcrel(bar+4) = 0x2398 (got entry for `bar`) - 0x33ac (.) + 4 = 0xf0efffff
+// %gotpcrel(bar-4) = 0x2398 (got entry for `bar`) - 0x33b0 (.) - 4 = 0xe4efffff
 // CHECK:      Contents of section .data:
 // CHECK-NEXT:  {{.*}} f0efffff f0efffff e4efffff
-  .word bar@GOTPCREL
-  .word bar@GOTPCREL+4
-  .word bar@GOTPCREL-4
+  .word %gotpcrel(bar)
+  .word %gotpcrel(bar+4)
+  .word %gotpcrel(bar-4)
 
 // WARN: relocation R_RISCV_GOT32_PCREL out of range: {{.*}} is not in [-2147483648, 2147483647]; references 'baz'
 // WARN: relocation R_RISCV_GOT32_PCREL out of range: {{.*}} is not in [-2147483648, 2147483647]; references 'baz'
-  .word baz@GOTPCREL+0xffffffff
-  .word baz@GOTPCREL-0xffffffff
+  .word %gotpcrel(baz+0xffffffff)
+  .word %gotpcrel(baz-0xffffffff)

llvm/include/llvm/CodeGen/AsmPrinter.h

@@ -497,7 +497,10 @@ class AsmPrinter : public MachineFunctionPass {
                      unsigned MaxBytesToEmit = 0) const;
 
   /// Lower the specified LLVM Constant to an MCExpr.
-  virtual const MCExpr *lowerConstant(const Constant *CV);
+  /// When BaseCV is present, we are lowering the element at BaseCV plus Offset.
+  virtual const MCExpr *lowerConstant(const Constant *CV,
+                                      const Constant *BaseCV = nullptr,
+                                      uint64_t Offset = 0);
 
   /// Print a general LLVM constant to the .s file.
   /// On AIX, when an alias refers to a sub-element of a global variable, the

llvm/include/llvm/CodeGen/TargetLoweringObjectFileImpl.h

@@ -40,7 +40,6 @@ class TargetLoweringObjectFileELF : public TargetLoweringObjectFile {
   uint8_t PLTRelativeSpecifier = 0;
 
 public:
-  TargetLoweringObjectFileELF();
   ~TargetLoweringObjectFileELF() override = default;
 
   void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
@@ -112,11 +111,22 @@ class TargetLoweringObjectFileELF : public TargetLoweringObjectFile {
   MCSection *getStaticDtorSection(unsigned Priority,
                                   const MCSymbol *KeySym) const override;
 
+  virtual const MCExpr *createTargetMCExpr(const MCExpr *Expr,
+                                           uint8_t Specifier) const {
+    return nullptr;
+  }
+  const MCExpr *
+  lowerSymbolDifference(const MCSymbol *LHS, const MCSymbol *RHS,
+                        int64_t Addend,
+                        std::optional<int64_t> PCRelativeOffset) const;
   const MCExpr *lowerRelativeReference(const GlobalValue *LHS,
-                                       const GlobalValue *RHS,
+                                       const GlobalValue *RHS, int64_t Addend,
+                                       std::optional<int64_t> PCRelativeOffset,
                                        const TargetMachine &TM) const override;
 
-  const MCExpr *lowerDSOLocalEquivalent(const DSOLocalEquivalent *Equiv,
+  const MCExpr *lowerDSOLocalEquivalent(const MCSymbol *LHS,
+                                        const MCSymbol *RHS, int64_t Addend,
+                                        std::optional<int64_t> PCRelativeOffset,
                                         const TargetMachine &TM) const override;
 
   MCSection *getSectionForCommandLines() const override;
@@ -206,7 +216,8 @@ class TargetLoweringObjectFileCOFF : public TargetLoweringObjectFile {
                                   const MCSymbol *KeySym) const override;
 
   const MCExpr *lowerRelativeReference(const GlobalValue *LHS,
-                                       const GlobalValue *RHS,
+                                       const GlobalValue *RHS, int64_t Addend,
+                                       std::optional<int64_t> PCRelativeOffset,
                                        const TargetMachine &TM) const override;
 
   /// Given a mergeable constant with the specified size and relocation

llvm/include/llvm/MC/MCParser/MCTargetAsmParser.h

@@ -396,6 +396,12 @@ class MCTargetAsmParser : public MCAsmParserExtension {
   virtual bool parsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc) {
     return getParser().parsePrimaryExpr(Res, EndLoc, nullptr);
   }
+  // Parse an expression in a data directive, possibly with a relocation
+  // specifier.
+  virtual bool parseDataExpr(const MCExpr *&Res) {
+    SMLoc EndLoc;
+    return getParser().parseExpression(Res, EndLoc);
+  }
 
   virtual bool parseRegister(MCRegister &Reg, SMLoc &StartLoc,
                              SMLoc &EndLoc) = 0;

llvm/include/llvm/Target/TargetLoweringObjectFile.h

@@ -51,7 +51,7 @@ class TargetLoweringObjectFile : public MCObjectFileInfo {
   bool SupportIndirectSymViaGOTPCRel = false;
   bool SupportGOTPCRelWithOffset = true;
   bool SupportDebugThreadLocalLocation = true;
-  bool SupportDSOLocalEquivalentLowering = false;
+  uint32_t PLTPCRelativeSpecifier = 0;
 
   /// PersonalityEncoding, LSDAEncoding, TTypeEncoding - Some encoding values
   /// for EH.
@@ -196,20 +196,19 @@ class TargetLoweringObjectFile : public MCObjectFileInfo {
   /// emitting the address in debug info.
   virtual const MCExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const;
 
-  virtual const MCExpr *lowerRelativeReference(const GlobalValue *LHS,
-                                               const GlobalValue *RHS,
-                                               const TargetMachine &TM) const {
+  virtual const MCExpr *lowerRelativeReference(
+      const GlobalValue *LHS, const GlobalValue *RHS, int64_t Addend,
+      std::optional<int64_t> PCRelativeOffset, const TargetMachine &TM) const {
     return nullptr;
   }
 
-  /// Target supports a native lowering of a dso_local_equivalent constant
-  /// without needing to replace it with equivalent IR.
-  bool supportDSOLocalEquivalentLowering() const {
-    return SupportDSOLocalEquivalentLowering;
-  }
+  /// Target supports a PC-relative relocation that references the PLT of a
+  /// function.
+  bool hasPLTPCRelative() const { return PLTPCRelativeSpecifier; }
 
-  virtual const MCExpr *lowerDSOLocalEquivalent(const DSOLocalEquivalent *Equiv,
-                                                const TargetMachine &TM) const {
+  virtual const MCExpr *lowerDSOLocalEquivalent(
+      const MCSymbol *LHS, const MCSymbol *RHS, int64_t Addend,
+      std::optional<int64_t> PCRelativeOffset, const TargetMachine &TM) const {
     return nullptr;
   }
 

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -3363,7 +3363,9 @@ void AsmPrinter::emitAlignment(Align Alignment, const GlobalObject *GV,
 // Constant emission.
 //===----------------------------------------------------------------------===//
 
-const MCExpr *AsmPrinter::lowerConstant(const Constant *CV) {
+const MCExpr *AsmPrinter::lowerConstant(const Constant *CV,
+                                        const Constant *BaseCV,
+                                        uint64_t Offset) {
   MCContext &Ctx = OutContext;
 
   if (CV->isNullValue() || isa<UndefValue>(CV))
@@ -3382,7 +3384,8 @@ const MCExpr *AsmPrinter::lowerConstant(const Constant *CV) {
     return lowerBlockAddressConstant(*BA);
 
   if (const auto *Equiv = dyn_cast<DSOLocalEquivalent>(CV))
-    return getObjFileLowering().lowerDSOLocalEquivalent(Equiv, TM);
+    return getObjFileLowering().lowerDSOLocalEquivalent(
+        getSymbol(Equiv->getGlobalValue()), nullptr, 0, std::nullopt, TM);
 
   if (const NoCFIValue *NC = dyn_cast<NoCFIValue>(CV))
     return MCSymbolRefExpr::create(getSymbol(NC->getGlobalValue()), Ctx);
@@ -3428,7 +3431,7 @@ const MCExpr *AsmPrinter::lowerConstant(const Constant *CV) {
     // is reasonable to treat their delta as a 32-bit value.
     [[fallthrough]];
   case Instruction::BitCast:
-    return lowerConstant(CE->getOperand(0));
+    return lowerConstant(CE->getOperand(0), BaseCV, Offset);
 
   case Instruction::IntToPtr: {
     const DataLayout &DL = getDataLayout();
@@ -3467,33 +3470,42 @@ const MCExpr *AsmPrinter::lowerConstant(const Constant *CV) {
   }
 
   case Instruction::Sub: {
-    GlobalValue *LHSGV;
-    APInt LHSOffset;
+    GlobalValue *LHSGV, *RHSGV;
+    APInt LHSOffset, RHSOffset;
     DSOLocalEquivalent *DSOEquiv;
     if (IsConstantOffsetFromGlobal(CE->getOperand(0), LHSGV, LHSOffset,
-                                   getDataLayout(), &DSOEquiv)) {
-      GlobalValue *RHSGV;
-      APInt RHSOffset;
-      if (IsConstantOffsetFromGlobal(CE->getOperand(1), RHSGV, RHSOffset,
-                                     getDataLayout())) {
-        const MCExpr *RelocExpr =
-            getObjFileLowering().lowerRelativeReference(LHSGV, RHSGV, TM);
-        if (!RelocExpr) {
-          const MCExpr *LHSExpr =
-              MCSymbolRefExpr::create(getSymbol(LHSGV), Ctx);
-          if (DSOEquiv &&
-              getObjFileLowering().supportDSOLocalEquivalentLowering())
-            LHSExpr =
-                getObjFileLowering().lowerDSOLocalEquivalent(DSOEquiv, TM);
-          RelocExpr = MCBinaryExpr::createSub(
-              LHSExpr, MCSymbolRefExpr::create(getSymbol(RHSGV), Ctx), Ctx);
-        }
-        int64_t Addend = (LHSOffset - RHSOffset).getSExtValue();
+                                   getDataLayout(), &DSOEquiv) &&
+        IsConstantOffsetFromGlobal(CE->getOperand(1), RHSGV, RHSOffset,
+                                   getDataLayout())) {
+      auto *LHSSym = getSymbol(LHSGV);
+      auto *RHSSym = getSymbol(RHSGV);
+      int64_t Addend = (LHSOffset - RHSOffset).getSExtValue();
+      std::optional<int64_t> PCRelativeOffset;
+      if (getObjFileLowering().hasPLTPCRelative() && RHSGV == BaseCV)
+        PCRelativeOffset = Offset;
+
+      // Try the generic symbol difference first.
+      const MCExpr *Res = getObjFileLowering().lowerRelativeReference(
+          LHSGV, RHSGV, Addend, PCRelativeOffset, TM);
+
+      // (ELF-specific) If the generic symbol difference does not apply, and
+      // LHS is a dso_local_equivalent of a dso_preemptable function,
+      // reference the PLT entry instead.
+      if (DSOEquiv && TM.getTargetTriple().isOSBinFormatELF() &&
+          !(LHSGV->isDSOLocal() || LHSGV->isImplicitDSOLocal()))
+        Res = getObjFileLowering().lowerDSOLocalEquivalent(
+            LHSSym, RHSSym, Addend, PCRelativeOffset, TM);
+
+      // Otherwise, return LHS-RHS+Addend.
+      if (!Res) {
+        Res =
+            MCBinaryExpr::createSub(MCSymbolRefExpr::create(LHSSym, Ctx),
+                                    MCSymbolRefExpr::create(RHSSym, Ctx), Ctx);
         if (Addend != 0)
-          RelocExpr = MCBinaryExpr::createAdd(
-              RelocExpr, MCConstantExpr::create(Addend, Ctx), Ctx);
-        return RelocExpr;
+          Res = MCBinaryExpr::createAdd(
+              Res, MCConstantExpr::create(Addend, Ctx), Ctx);
       }
+      return Res;
     }
 
     const MCExpr *LHS = lowerConstant(CE->getOperand(0));
@@ -4023,7 +4035,7 @@ static void emitGlobalConstantImpl(const DataLayout &DL, const Constant *CV,
 
   // Otherwise, it must be a ConstantExpr.  Lower it to an MCExpr, then emit it
   // thread the streamer with EmitValue.
-  const MCExpr *ME = AP.lowerConstant(CV);
+  const MCExpr *ME = AP.lowerConstant(CV, BaseCV, Offset);
 
   // Since lowerConstant already folded and got rid of all IR pointer and
   // integer casts, detect GOT equivalent accesses by looking into the MCExpr

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -115,10 +115,6 @@ static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
 //                                  ELF
 //===----------------------------------------------------------------------===//
 
-TargetLoweringObjectFileELF::TargetLoweringObjectFileELF() {
-  SupportDSOLocalEquivalentLowering = true;
-}
-
 void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
                                              const TargetMachine &TgtM) {
   TargetLoweringObjectFile::Initialize(Ctx, TgtM);
@@ -1174,9 +1170,37 @@ MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
                                   KeySym);
 }
 
+const MCExpr *TargetLoweringObjectFileELF::lowerSymbolDifference(
+    const MCSymbol *LHS, const MCSymbol *RHS, int64_t Addend,
+    std::optional<int64_t> PCRelativeOffset) const {
+  auto &Ctx = getContext();
+  const MCExpr *Res;
+  // Return a relocatable expression with the PLT specifier, %plt(GV) or
+  // %plt(GV-RHS).
+  if (PCRelativeOffset && PLTPCRelativeSpecifier) {
+    Res = MCSymbolRefExpr::create(LHS, Ctx);
+    // The current location is RHS plus *PCRelativeOffset. Compensate for it.
+    Addend += *PCRelativeOffset;
+    if (Addend)
+      Res = MCBinaryExpr::createAdd(Res, MCConstantExpr::create(Addend, Ctx),
+                                    Ctx);
+    return createTargetMCExpr(Res, PLTPCRelativeSpecifier);
+  }
+
+  if (!PLTRelativeSpecifier)
+    return nullptr;
+  Res = MCBinaryExpr::createSub(
+      MCSymbolRefExpr::create(LHS, PLTRelativeSpecifier, Ctx),
+      MCSymbolRefExpr::create(RHS, Ctx), Ctx);
+  if (Addend)
+    Res =
+        MCBinaryExpr::createAdd(Res, MCConstantExpr::create(Addend, Ctx), Ctx);
+  return Res;
+}
+
 const MCExpr *TargetLoweringObjectFileELF::lowerRelativeReference(
-    const GlobalValue *LHS, const GlobalValue *RHS,
-    const TargetMachine &TM) const {
+    const GlobalValue *LHS, const GlobalValue *RHS, int64_t Addend,
+    std::optional<int64_t> PCRelativeOffset, const TargetMachine &TM) const {
   // We may only use a PLT-relative relocation to refer to unnamed_addr
   // functions.
   if (!LHS->hasGlobalUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
@@ -1188,24 +1212,22 @@ const MCExpr *TargetLoweringObjectFileELF::lowerRelativeReference(
       RHS->isThreadLocal())
     return nullptr;
 
-  return MCBinaryExpr::createSub(
-      MCSymbolRefExpr::create(TM.getSymbol(LHS), PLTRelativeSpecifier,
-                              getContext()),
-      MCSymbolRefExpr::create(TM.getSymbol(RHS), getContext()), getContext());
+  return lowerSymbolDifference(TM.getSymbol(LHS), TM.getSymbol(RHS), Addend,
+                               PCRelativeOffset);
 }
 
+// Reference the PLT entry of a function, optionally with a subtrahend (`RHS`).
 const MCExpr *TargetLoweringObjectFileELF::lowerDSOLocalEquivalent(
-    const DSOLocalEquivalent *Equiv, const TargetMachine &TM) const {
-  assert(supportDSOLocalEquivalentLowering());
-
-  const auto *GV = Equiv->getGlobalValue();
-
-  // A PLT entry is not needed for dso_local globals.
-  if (GV->isDSOLocal() || GV->isImplicitDSOLocal())
-    return MCSymbolRefExpr::create(TM.getSymbol(GV), getContext());
-
-  return MCSymbolRefExpr::create(TM.getSymbol(GV), PLTRelativeSpecifier,
-                                 getContext());
+    const MCSymbol *LHS, const MCSymbol *RHS, int64_t Addend,
+    std::optional<int64_t> PCRelativeOffset, const TargetMachine &TM) const {
+  if (RHS)
+    return lowerSymbolDifference(LHS, RHS, Addend, PCRelativeOffset);
+
+  // Only the legacy MCSymbolRefExpr::VariantKind approach is implemented.
+  // Reference LHS@plt or LHS@plt - RHS.
+  if (PLTRelativeSpecifier)
+    return MCSymbolRefExpr::create(LHS, PLTRelativeSpecifier, getContext());
+  return nullptr;
 }
 
 MCSection *TargetLoweringObjectFileELF::getSectionForCommandLines() const {
@@ -2044,8 +2066,8 @@ MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
 }
 
 const MCExpr *TargetLoweringObjectFileCOFF::lowerRelativeReference(
-    const GlobalValue *LHS, const GlobalValue *RHS,
-    const TargetMachine &TM) const {
+    const GlobalValue *LHS, const GlobalValue *RHS, int64_t Addend,
+    std::optional<int64_t> PCRelativeOffset, const TargetMachine &TM) const {
   const Triple &T = TM.getTargetTriple();
   if (T.isOSCygMing())
     return nullptr;
@@ -2069,9 +2091,12 @@ const MCExpr *TargetLoweringObjectFileCOFF::lowerRelativeReference(
       cast<GlobalVariable>(RHS)->hasInitializer() || RHS->hasSection())
     return nullptr;
 
-  return MCSymbolRefExpr::create(TM.getSymbol(LHS),
-                                 MCSymbolRefExpr::VK_COFF_IMGREL32,
-                                 getContext());
+  const MCExpr *Res = MCSymbolRefExpr::create(
+      TM.getSymbol(LHS), MCSymbolRefExpr::VK_COFF_IMGREL32, getContext());
+  if (Addend != 0)
+    Res = MCBinaryExpr::createAdd(
+        Res, MCConstantExpr::create(Addend, getContext()), getContext());
+  return Res;
 }
 
 static std::string APIntToHexString(const APInt &AI) {

llvm/lib/MC/MCAssembler.cpp

@@ -237,7 +237,7 @@ bool MCAssembler::evaluateFixup(const MCFixup &Fixup, const MCFragment *DF,
   // A linker relaxation target may emit ADD/SUB relocations for A-B+C. Let
   // recordRelocation handle non-VK_None cases like A@plt-B+C.
   if (!IsResolved && Target.getSymA() && Target.getSubSym() &&
-      Target.getSymA()->getKind() == MCSymbolRefExpr::VK_None &&
+      Target.getRefKind() == 0 &&
       getBackend().handleAddSubRelocations(*this, *DF, Fixup, Target, Value))
     return true;
 

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -3144,7 +3144,7 @@ bool AsmParser::parseDirectiveValue(StringRef IDVal, unsigned Size) {
   auto parseOp = [&]() -> bool {
     const MCExpr *Value;
     SMLoc ExprLoc = getLexer().getLoc();
-    if (checkForValidSection() || parseExpression(Value))
+    if (checkForValidSection() || getTargetParser().parseDataExpr(Value))
       return true;
     // Special case constant expressions to match code generator.
     if (const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(Value)) {