[RISCV] Implement jump pseudo-instruction

Summary:
Implements the jump pseudo-instruction, which is used in e.g. the Linux kernel.

Reviewers: asb, lenary
Reviewed By: lenary
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73178

lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -138,6 +138,7 @@ class RISCVAsmParser : public MCTargetAsmParser {
   OperandMatchResultTy parseOperandWithModifier(OperandVector &Operands);
   OperandMatchResultTy parseBareSymbol(OperandVector &Operands);
   OperandMatchResultTy parseCallSymbol(OperandVector &Operands);
+  OperandMatchResultTy parsePseudoJumpSymbol(OperandVector &Operands);
   OperandMatchResultTy parseJALOffset(OperandVector &Operands);
 
   bool parseOperand(OperandVector &Operands, StringRef Mnemonic);
@@ -337,6 +338,16 @@ public:
             VK == RISCVMCExpr::VK_RISCV_CALL_PLT);
   }
 
+  bool isPseudoJumpSymbol() const {
+    int64_t Imm;
+    RISCVMCExpr::VariantKind VK = RISCVMCExpr::VK_RISCV_None;
+    // Must be of 'immediate' type but not a constant.
+    if (!isImm() || evaluateConstantImm(getImm(), Imm, VK))
+      return false;
+    return RISCVAsmParser::classifySymbolRef(getImm(), VK, Imm) &&
+           VK == RISCVMCExpr::VK_RISCV_CALL;
+  }
+
   bool isTPRelAddSymbol() const {
     int64_t Imm;
     RISCVMCExpr::VariantKind VK = RISCVMCExpr::VK_RISCV_None;
@@ -976,6 +987,10 @@ bool RISCVAsmParser::MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
     SMLoc ErrorLoc = ((RISCVOperand &)*Operands[ErrorInfo]).getStartLoc();
     return Error(ErrorLoc, "operand must be a bare symbol name");
   }
+  case Match_InvalidPseudoJumpSymbol: {
+    SMLoc ErrorLoc = ((RISCVOperand &)*Operands[ErrorInfo]).getStartLoc();
+    return Error(ErrorLoc, "operand must be a valid jump target");
+  }
   case Match_InvalidCallSymbol: {
     SMLoc ErrorLoc = ((RISCVOperand &)*Operands[ErrorInfo]).getStartLoc();
     return Error(ErrorLoc, "operand must be a bare symbol name");
@@ -1287,6 +1302,27 @@ OperandMatchResultTy RISCVAsmParser::parseCallSymbol(OperandVector &Operands) {
   return MatchOperand_Success;
 }
 
+OperandMatchResultTy
+RISCVAsmParser::parsePseudoJumpSymbol(OperandVector &Operands) {
+  SMLoc S = getLoc();
+  SMLoc E = SMLoc::getFromPointer(S.getPointer() - 1);
+  const MCExpr *Res;
+
+  if (getParser().parseExpression(Res))
+    return MatchOperand_ParseFail;
+
+  if (Res->getKind() != MCExpr::ExprKind::SymbolRef ||
+      cast<MCSymbolRefExpr>(Res)->getKind() ==
+          MCSymbolRefExpr::VariantKind::VK_PLT) {
+    Error(S, "operand must be a valid jump target");
+    return MatchOperand_ParseFail;
+  }
+
+  Res = RISCVMCExpr::create(Res, RISCVMCExpr::VK_RISCV_CALL, getContext());
+  Operands.push_back(RISCVOperand::createImm(Res, S, E, isRV64()));
+  return MatchOperand_Success;
+}
+
 OperandMatchResultTy RISCVAsmParser::parseJALOffset(OperandVector &Operands) {
   // Parsing jal operands is fiddly due to the `jal foo` and `jal ra, foo`
   // both being acceptable forms. When parsing `jal ra, foo` this function

lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp

@@ -89,9 +89,9 @@ MCCodeEmitter *llvm::createRISCVMCCodeEmitter(const MCInstrInfo &MCII,
   return new RISCVMCCodeEmitter(Ctx, MCII);
 }
 
-// Expand PseudoCALL(Reg) and PseudoTAIL to AUIPC and JALR with relocation
-// types. We expand PseudoCALL(Reg) and PseudoTAIL while encoding, meaning AUIPC
-// and JALR won't go through RISCV MC to MC compressed instruction
+// Expand PseudoCALL(Reg), PseudoTAIL and PseudoJump to AUIPC and JALR with
+// relocation types. We those pseudo-instructions while encoding them, meaning
+// AUIPC and JALR won't go through RISCV MC to MC compressed instruction
 // transformation. This is acceptable because AUIPC has no 16-bit form and
 // C_JALR have no immediate operand field.  We let linker relaxation deal with
 // it. When linker relaxation enabled, AUIPC and JALR have chance relax to JAL.
@@ -108,9 +108,12 @@ void RISCVMCCodeEmitter::expandFunctionCall(const MCInst &MI, raw_ostream &OS,
   } else if (MI.getOpcode() == RISCV::PseudoCALLReg) {
     Func = MI.getOperand(1);
     Ra = MI.getOperand(0).getReg();
-  } else {
+  } else if (MI.getOpcode() == RISCV::PseudoCALL) {
     Func = MI.getOperand(0);
     Ra = RISCV::X1;
+  } else if (MI.getOpcode() == RISCV::PseudoJump) {
+    Func = MI.getOperand(1);
+    Ra = MI.getOperand(0).getReg();
   }
   uint32_t Binary;
 
@@ -125,8 +128,9 @@ void RISCVMCCodeEmitter::expandFunctionCall(const MCInst &MI, raw_ostream &OS,
   Binary = getBinaryCodeForInstr(TmpInst, Fixups, STI);
   support::endian::write(OS, Binary, support::little);
 
-  if (MI.getOpcode() == RISCV::PseudoTAIL)
-    // Emit JALR X0, X6, 0
+  if (MI.getOpcode() == RISCV::PseudoTAIL ||
+      MI.getOpcode() == RISCV::PseudoJump)
+    // Emit JALR X0, Ra, 0
     TmpInst = MCInstBuilder(RISCV::JALR).addReg(RISCV::X0).addReg(Ra).addImm(0);
   else
     // Emit JALR Ra, Ra, 0
@@ -182,7 +186,8 @@ void RISCVMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
 
   if (MI.getOpcode() == RISCV::PseudoCALLReg ||
       MI.getOpcode() == RISCV::PseudoCALL ||
-      MI.getOpcode() == RISCV::PseudoTAIL) {
+      MI.getOpcode() == RISCV::PseudoTAIL ||
+      MI.getOpcode() == RISCV::PseudoJump) {
     expandFunctionCall(MI, OS, Fixups, STI);
     MCNumEmitted += 2;
     return;

lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -473,6 +473,7 @@ unsigned RISCVInstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
     return 0;
   case RISCV::PseudoCALLReg:
   case RISCV::PseudoCALL:
+  case RISCV::PseudoJump:
   case RISCV::PseudoTAIL:
   case RISCV::PseudoLLA:
   case RISCV::PseudoLA:

lib/Target/RISCV/RISCVInstrInfo.td

@@ -222,6 +222,18 @@ def call_symbol : Operand<XLenVT> {
   let ParserMatchClass = CallSymbol;
 }
 
+def PseudoJumpSymbol : AsmOperandClass {
+  let Name = "PseudoJumpSymbol";
+  let RenderMethod = "addImmOperands";
+  let DiagnosticType = "InvalidPseudoJumpSymbol";
+  let ParserMethod = "parsePseudoJumpSymbol";
+}
+
+// A bare symbol used for pseudo jumps only.
+def pseudo_jump_symbol : Operand<XLenVT> {
+  let ParserMatchClass = PseudoJumpSymbol;
+}
+
 def TPRelAddSymbol : AsmOperandClass {
   let Name = "TPRelAddSymbol";
   let RenderMethod = "addImmOperands";
@@ -968,6 +980,12 @@ def : Pat<(riscv_tail (iPTR tglobaladdr:$dst)),
 def : Pat<(riscv_tail (iPTR texternalsym:$dst)),
           (PseudoTAIL texternalsym:$dst)>;
 
+let isCall = 0, isBarrier = 0, isCodeGenOnly = 0, hasSideEffects = 0,
+    mayStore = 0, mayLoad = 0 in
+def PseudoJump : Pseudo<(outs GPR:$rd), (ins pseudo_jump_symbol:$target), []> {
+  let AsmString = "jump\t$target, $rd";
+}
+
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0, isCodeGenOnly = 0,
     isAsmParserOnly = 1 in
 def PseudoLLA : Pseudo<(outs GPR:$dst), (ins bare_symbol:$src), [],

test/MC/RISCV/pseudo-jump-invalid.s

@@ -0,0 +1,5 @@
+# RUN: not llvm-mc -triple riscv32 < %s 2>&1 | FileCheck %s
+
+jump 1234, x31 # CHECK: :[[@LINE]]:6: error: operand must be a valid jump target
+jump foo@plt, x31 # CHECK: :[[@LINE]]:6: error: operand must be a valid jump target
+jump %pcrel_lo(1234), x31 # CHECK: :[[@LINE]]:6: error: unknown token in expression

test/MC/RISCV/pseudo-jump.s

@@ -0,0 +1,28 @@
+# RUN: llvm-mc -filetype=obj -triple riscv32 < %s \
+# RUN:     | llvm-objdump -d - | FileCheck -check-prefix=INSTR %s
+# RUN: llvm-mc -filetype=obj -triple riscv32 < %s \
+# RUN:     | llvm-readobj -r | FileCheck -check-prefix=RELOC %s
+# RUN: llvm-mc -triple riscv32 < %s -show-encoding \
+# RUN:     | FileCheck -check-prefix=FIXUP %s
+
+.long foo
+
+jump foo, x31
+# RELOC: R_RISCV_CALL foo 0x0
+# INSTR: auipc t6, 0
+# INSTR: jr  t6
+# FIXUP: fixup A - offset: 0, value: foo, kind: fixup_riscv_call
+
+# Ensure that jumps to symbols whose names coincide with register names work.
+
+jump zero, x1
+# RELOC: R_RISCV_CALL zero 0x0
+# INSTR: auipc ra, 0
+# INSTR: ret
+# FIXUP: fixup A - offset: 0, value: zero, kind: fixup_riscv_call
+
+1:
+jump 1b, x31
+# INSTR: auipc t6, 0
+# INSTR: jr  t6
+# FIXUP: fixup A - offset: 0, value: .Ltmp0, kind: fixup_riscv_call