[RISC-V][MC] Introduce initial support for Y extension (CHERI)

This adds MC-level support for most of the base Y extension instructions,
restricted to the execution-mode-independent subset. The Y extension
(CHERI for RISC-V) also introduces an execution mode that determines
whether certain register operands use the full extended register or only
the address subset (the current XLEN registers). The instructions that
depend on execution mode (loads/stores/jumps + AUIPC) will be added in
the next commit in this stack of changes.

Co-authored-by: Jessica Clarke <[email protected]>
Co-authored-by: Alexander Richardson <[email protected]>
Co-authored-by: Petr Vesely <[email protected]>

Author: 3 people

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -491,6 +491,11 @@ struct RISCVOperand final : public MCParsedAsmOperand {
            RISCVMCRegisterClasses[RISCV::GPRRegClassID].contains(Reg.RegNum);
   }
 
+  bool isYGPR() const {
+    return Kind == KindTy::Register &&
+           RISCVMCRegisterClasses[RISCV::YGPRRegClassID].contains(Reg.RegNum);
+  }
+
   bool isGPRPair() const {
     return Kind == KindTy::Register &&
            RISCVMCRegisterClasses[RISCV::GPRPairRegClassID].contains(
@@ -767,6 +772,11 @@ struct RISCVOperand final : public MCParsedAsmOperand {
     });
   }
 
+  bool isUImm7Srliy() const {
+    return isUImmPred(
+        [this](int64_t Imm) { return isRV64Expr() ? Imm == 64 : Imm == 32; });
+  }
+
   bool isUImm8GE32() const {
     return isUImmPred([](int64_t Imm) { return isUInt<8>(Imm) && Imm >= 32; });
   }
@@ -799,6 +809,29 @@ struct RISCVOperand final : public MCParsedAsmOperand {
     return IsConstantImm && isInt<N>(fixImmediateForRV32(Imm, isRV64Expr()));
   }
 
+  bool isYBNDSWImm() const {
+    if (!isExpr())
+      return false;
+
+    int64_t Imm;
+    bool IsConstantImm = evaluateConstantExpr(getExpr(), Imm);
+    if (!IsConstantImm)
+      return false;
+    // The immediate is encoded using `((imm[7:0] + 257) << imm[9:8]) - 256`
+    // which gives the following valid ranges:
+    if (Imm < 1)
+      return false;
+    if (Imm <= 256)
+      return true;
+    if (Imm <= 768)
+      return (Imm % 2) == 0;
+    if (Imm <= 1792)
+      return (Imm % 4) == 0;
+    if (Imm <= 3840)
+      return (Imm % 8) == 0;
+    return false;
+  }
+
   template <class Pred> bool isSImmPred(Pred p) const {
     int64_t Imm;
     if (!isExpr())
@@ -1306,6 +1339,11 @@ static MCRegister convertFPR64ToFPR128(MCRegister Reg) {
   return Reg - RISCV::F0_D + RISCV::F0_Q;
 }
 
+static MCRegister convertGPRToYGPR(MCRegister Reg) {
+  assert(Reg >= RISCV::X0 && Reg <= RISCV::X31 && "Invalid register");
+  return Reg - RISCV::X0 + RISCV::X0_Y;
+}
+
 static MCRegister convertVRToVRMx(const MCRegisterInfo &RI, MCRegister Reg,
                                   unsigned Kind) {
   unsigned RegClassID;
@@ -1333,7 +1371,11 @@ unsigned RISCVAsmParser::validateTargetOperandClass(MCParsedAsmOperand &AsmOp,
   bool IsRegFPR64C =
       RISCVMCRegisterClasses[RISCV::FPR64CRegClassID].contains(Reg);
   bool IsRegVR = RISCVMCRegisterClasses[RISCV::VRRegClassID].contains(Reg);
-
+  if (Op.isGPR() && Kind == MCK_YGPR) {
+    // GPR and capability GPR use the same register names, convert if required.
+    Op.Reg.RegNum = convertGPRToYGPR(Reg);
+    return Match_Success;
+  }
   if (IsRegFPR64 && Kind == MCK_FPR128) {
     Op.Reg.RegNum = convertFPR64ToFPR128(Reg);
     return Match_Success;
@@ -1708,6 +1750,18 @@ bool RISCVAsmParser::matchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
         ErrorLoc,
         "stack adjustment is invalid for this instruction and register list");
   }
+  case Match_InvalidYBNDSWImm: {
+    const SMLoc ErrorLoc = ((RISCVOperand &)*Operands[ErrorInfo]).getStartLoc();
+    return Error(ErrorLoc, "immediate must be an integer in the range "
+                           "[1, 256], a multiple of 2 in the range [258, 768], "
+                           "a multiple of 4 in the range [772, 1792], or "
+                           "a multiple of 8 in the range [1800, 3840]");
+  }
+  case Match_InvalidUImm7Srliy: {
+    const SMLoc ErrorLoc = ((RISCVOperand &)*Operands[ErrorInfo]).getStartLoc();
+    return Error(ErrorLoc, "immediate must be an integer equal to XLEN (" +
+                               Twine(isRV64() ? "64" : "32") + ")");
+  }
   }
 
   if (const char *MatchDiag = getMatchKindDiag((RISCVMatchResultTy)Result)) {

llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp

@@ -91,6 +91,19 @@ static DecodeStatus DecodeGPRRegisterClass(MCInst &Inst, uint32_t RegNo,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus DecodeYGPRRegisterClass(MCInst &Inst, uint32_t RegNo,
+                                            uint64_t Address,
+                                            const MCDisassembler *Decoder) {
+  bool IsRVE = Decoder->getSubtargetInfo().hasFeature(RISCV::FeatureStdExtE);
+
+  if (RegNo >= 32 || (IsRVE && RegNo >= 16))
+    return MCDisassembler::Fail;
+
+  MCRegister Reg = RISCV::X0_Y + RegNo;
+  Inst.addOperand(MCOperand::createReg(Reg));
+  return MCDisassembler::Success;
+}
+
 static DecodeStatus DecodeGPRF16RegisterClass(MCInst &Inst, uint32_t RegNo,
                                               uint64_t Address,
                                               const MCDisassembler *Decoder) {
@@ -416,6 +429,15 @@ static DecodeStatus DecodeTRM4RegisterClass(MCInst &Inst, uint32_t RegNo,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus DecodeYBNDSWImm(MCInst &Inst, uint64_t Imm, int64_t Address,
+                                    const MCDisassembler *Decoder) {
+  assert(isUInt<10>(Imm) && "Invalid immediate");
+  const uint32_t Shift = Imm >> 8;
+  uint64_t Result = (((Imm & maxUIntN(8)) + 257) << Shift) - 256;
+  Inst.addOperand(MCOperand::createImm(Result));
+  return MCDisassembler::Success;
+}
+
 static DecodeStatus decodeVMaskReg(MCInst &Inst, uint32_t RegNo,
                                    uint64_t Address,
                                    const MCDisassembler *Decoder) {
@@ -497,6 +519,20 @@ static DecodeStatus decodeUImmLog2XLenOperand(MCInst &Inst, uint32_t Imm,
   return MCDisassembler::Success;
 }
 
+static DecodeStatus decodeUImm7SrliyOperand(MCInst &Inst, uint32_t Imm,
+                                            int64_t Address,
+                                            const MCDisassembler *Decoder) {
+  assert(isUInt<7>(Imm) && "Invalid immediate");
+
+  uint32_t ExpectedValue =
+      Decoder->getSubtargetInfo().hasFeature(RISCV::Feature64Bit) ? 64 : 32;
+  if (Imm != ExpectedValue)
+    return MCDisassembler::Fail;
+
+  Inst.addOperand(MCOperand::createImm(Imm));
+  return MCDisassembler::Success;
+}
+
 template <unsigned N>
 static DecodeStatus decodeUImmNonZeroOperand(MCInst &Inst, uint32_t Imm,
                                              int64_t Address,
@@ -699,6 +735,9 @@ static constexpr DecoderListEntry DecoderList32[]{
     {DecoderTableXAndes32, XAndesGroup, "Andes extensions"},
     {DecoderTableXSMT32, XSMTGroup, "SpacemiT extensions"},
     // Standard Extensions
+    {DecoderTableRVYOnly32,
+     {RISCV::FeatureStdExtY},
+     "RVY-only standard 32-bit instructions"},
     {DecoderTable32, {}, "standard 32-bit instructions"},
     {DecoderTableRV32Only32, {}, "RV32-only standard 32-bit instructions"},
     {DecoderTableZfinx32, {}, "Zfinx (Float in Integer)"},

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -320,6 +320,7 @@ enum OperandType : unsigned {
   OPERAND_UIMM7,
   OPERAND_UIMM7_LSB00,
   OPERAND_UIMM7_LSB000,
+  OPERAND_UIMM7_SRLIY,
   OPERAND_UIMM8_LSB00,
   OPERAND_UIMM8,
   OPERAND_UIMM8_LSB000,

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp

@@ -105,6 +105,10 @@ class RISCVMCCodeEmitter : public MCCodeEmitter {
                          SmallVectorImpl<MCFixup> &Fixups,
                          const MCSubtargetInfo &STI) const;
 
+  unsigned getYBNDSWImmOpValue(const MCInst &MI, unsigned OpNo,
+                               SmallVectorImpl<MCFixup> &Fixups,
+                               const MCSubtargetInfo &STI) const;
+
   unsigned getVMaskReg(const MCInst &MI, unsigned OpNo,
                        SmallVectorImpl<MCFixup> &Fixups,
                        const MCSubtargetInfo &STI) const;
@@ -718,6 +722,31 @@ uint64_t RISCVMCCodeEmitter::getImmOpValue(const MCInst &MI, unsigned OpNo,
   return 0;
 }
 
+unsigned
+RISCVMCCodeEmitter::getYBNDSWImmOpValue(const MCInst &MI, unsigned OpNo,
+                                        SmallVectorImpl<MCFixup> &Fixups,
+                                        const MCSubtargetInfo &STI) const {
+  unsigned Imm = getImmOpValue(MI, OpNo, Fixups, STI);
+  // The 10-bit immediate is encoded as `((imm[7:0] + 257) << imm[9:8]) - 256`.
+  if (Imm <= 256) {
+    assert(Imm > 0); // 1, 2, ..., 255, 256
+    return Imm - 1;
+  }
+  if (Imm <= 768) {
+    assert(Imm % 2 == 0); // 258, 260, ..., 766, 768
+    return ((Imm - 258) >> 1) | (1 << 8);
+  }
+  if (Imm <= 1792) {
+    assert(Imm % 4 == 0); // 772, 776, ..., 1788, 1792
+    return ((Imm - 772) >> 2) | (2 << 8);
+  }
+  if (Imm <= 3840) {
+    assert(Imm % 8 == 0); // 1800, 1808, ..., 3832, 3840
+    return ((Imm - 1800) >> 3) | (3 << 8);
+  }
+  llvm_unreachable("Invalid immediate for YBNDSWI");
+}
+
 unsigned RISCVMCCodeEmitter::getVMaskReg(const MCInst &MI, unsigned OpNo,
                                          SmallVectorImpl<MCFixup> &Fixups,
                                          const MCSubtargetInfo &STI) const {

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -60,10 +60,9 @@ class RISCVExtensionBitmask<bits<3> groupID, int bitPos> {
 
 // Version of RISCVExtension to be used for Experimental extensions. This
 // sets the Experimental flag and prepends experimental- to the -mattr name.
-class RISCVExperimentalExtension<int major, int minor, string desc,
-                                 list<SubtargetFeature> implies = [],
-                                 string fieldname = !subst("Feature", "Has", NAME),
-                                 string value = "true">
+class RISCVExperimentalExtension<
+    int major, int minor, string desc, list<SubtargetFeature> implies = [],
+    string fieldname = !subst("Feature", "Has", NAME), string value = "true">
     : RISCVExtension<major, minor, desc, implies, fieldname, value, true> {
   let Experimental = true;
 }
@@ -1145,7 +1144,7 @@ def IsCapMode
     : Predicate<"Subtarget->isCapMode()">,
       AssemblerPredicate<(all_of FeatureCapMode), "Capability Pointer Mode">;
 def NotCapMode : Predicate<"!Subtarget->isCapMode()">,
-                 AssemblerPredicate<(all_of(not FeatureCapMode)),
+                 AssemblerPredicate<(all_of (not FeatureCapMode)),
                                     "Not Capability Pointer Mode">;
 
 //===----------------------------------------------------------------------===//

llvm/lib/Target/RISCV/RISCVInstrFormatsY.td

@@ -0,0 +1,77 @@
+//===-- RISCVInstrFormatsY.td --------------------------------*- tablegen -*-=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file describes the RISC-V Y extension instruction formats.
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+// Operand definitions.
+//===----------------------------------------------------------------------===//
+
+def YBNDSWImmOperand : AsmOperandClass {
+  let Name = "YBNDSWImm";
+  let RenderMethod = "addImmOperands";
+  let DiagnosticType = "InvalidYBNDSWImm";
+}
+
+def ybndsw_imm : Operand<XLenVT>, ImmLeaf<XLenVT, [{
+  return (Imm >= 1 && Imm <= 256) ||
+         (Imm >= 258 && Imm <= 768 && (Imm % 2) == 0) ||
+         (Imm >= 772 && Imm <= 1792 && (Imm % 4) == 0) ||
+         (Imm >= 1800 && Imm <= 3840 && (Imm % 8) == 0);
+}]> {
+  let EncoderMethod = "getYBNDSWImmOpValue";
+  let ParserMatchClass = YBNDSWImmOperand;
+  let DecoderMethod = "DecodeYBNDSWImm";
+  let MIOperandInfo = (ops i32imm);
+}
+
+def uimm7_srliy : RISCVUImmOp<7>, ImmLeaf<XLenVT, [{
+  return Subtarget->is64Bit() ? Imm == 64 : Imm == 32;
+}]> {
+  let ParserMatchClass = UImmAsmOperand<7, "Srliy">;
+  let DecoderMethod = "decodeUImm7SrliyOperand";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (!MCOp.evaluateAsConstantImm(Imm))
+      return false;
+    return Subtarget->is64Bit() ? Imm == 64 : Imm == 32;
+  }];
+  let OperandType = "OPERAND_UIMM7_SRLIY";
+}
+
+//===----------------------------------------------------------------------===//
+// Instruction Formats
+//===----------------------------------------------------------------------===//
+
+// Like an RVInstR, except rs2 is now an additional function code.
+class RVYInstSrcDst<bits<7> funct7, bits<5> funct5, bits<3> funct3,
+                    RISCVOpcode opcode, dag outs, dag ins, string opcodestr,
+                    string argstr>
+    : RVInst<outs, ins, opcodestr, argstr, [], InstFormatR> {
+  bits<5> rs1;
+  bits<5> rd;
+
+  let Inst{31 -25} = funct7;
+  let Inst{24 -20} = funct5;
+  let Inst{19 -15} = rs1;
+  let Inst{14 -12} = funct3;
+  let Inst{11 -7} = rd;
+  let Inst{6 -0} = opcode.Value;
+}
+
+class RVYInstSetBoundsImmFmt<dag outs, dag ins, string opcodestr, string argstr>
+    : RVInstIBase<0b011, OPC_OP_IMM_32, outs, ins, opcodestr, argstr> {
+  bits<5> rd;
+  bits<5> rs1;
+  bits<10> imm;
+
+  let Inst{31 -30} = 0b00;
+  let Inst{29 -20} = imm;
+}

llvm/lib/Target/RISCV/RISCVInstrInfo.td

@@ -2363,6 +2363,9 @@ include "RISCVInstrInfoZicfiss.td"
 // Short Forward Branch
 include "RISCVInstrInfoSFB.td"
 
+// CHERI
+include "RISCVInstrInfoY.td"
+
 //===----------------------------------------------------------------------===//
 // Vendor extensions
 //===----------------------------------------------------------------------===//