[RISCV] Add MIPS extensions

Adding two extensions for MIPS p8700 CPU:
  1. cmove (conditional move)
  2. lsp (load/store pair)

The official product page here:
https://mips.com/products/hardware/p8700

Author: djtodoro

clang/include/clang/Driver/Options.td

@@ -4977,6 +4977,10 @@ def msave_restore : Flag<["-"], "msave-restore">, Group<m_riscv_Features_Group>,
 def mno_save_restore : Flag<["-"], "mno-save-restore">, Group<m_riscv_Features_Group>,
   HelpText<"Disable using library calls for save and restore">;
 } // let Flags = [TargetSpecific]
+def mload_store_pairs : Flag<["-"], "mload-store-pairs">, Group<m_riscv_Features_Group>;
+def mno_load_store_pairs : Flag<["-"], "mno-load-store-pairs">, Group<m_riscv_Features_Group>;
+def mccmov : Flag<["-"], "mccmov">, Group<m_riscv_Features_Group>;
+def mno_ccmov : Flag<["-"], "mno-ccmov">, Group<m_riscv_Features_Group>;
 let Flags = [TargetSpecific] in {
 def menable_experimental_extensions : Flag<["-"], "menable-experimental-extensions">, Group<m_Group>,
   HelpText<"Enable use of experimental RISC-V extensions.">;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2185,6 +2185,21 @@ void Clang::AddRISCVTargetArgs(const ArgList &Args,
       CmdArgs.push_back(A->getValue());
   }
 
+  if (Arg *A = Args.getLastArg(options::OPT_mload_store_pairs,
+                               options::OPT_mno_load_store_pairs)) {
+    if (A->getOption().matches(options::OPT_mload_store_pairs)) {
+      CmdArgs.push_back("-mllvm");
+      CmdArgs.push_back("-riscv-load-store-pairs=1");
+    }
+  }
+
+  if (Arg *A = Args.getLastArg(options::OPT_mccmov, options::OPT_mno_ccmov)) {
+    if (A->getOption().matches(options::OPT_mno_ccmov)) {
+      CmdArgs.push_back("-mllvm");
+      CmdArgs.push_back("-riscv-ccmov=0");
+    }
+  }
+
   // Handle -mrvv-vector-bits=<bits>
   if (Arg *A = Args.getLastArg(options::OPT_mrvv_vector_bits_EQ)) {
     StringRef Val = A->getValue();

llvm/docs/RISCVUsage.rst

@@ -456,6 +456,12 @@ The current vendor extensions supported are:
 ``experimental-Xqcisls``
   LLVM implements `version 0.2 of the Qualcomm uC Scaled Load Store extension specification <https://github.com/quic/riscv-unified-db/releases/latest>`__ by Qualcomm.  All instructions are prefixed with `qc.` as described in the specification. These instructions are only available for riscv32.
 
+``Xmipscmove``
+  LLVM implements conditional move for the `p8700 processor <https://mips.com/products/hardware/p8700/>` by MIPS.
+
+``Xmipslsp``
+  LLVM implements load/store pair instructions for the `p8700 processor <https://mips.com/products/hardware/p8700/>` by MIPS.
+
 Experimental C Intrinsics
 =========================
 

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

@@ -877,6 +877,16 @@ struct RISCVOperand final : public MCParsedAsmOperand {
            VK == RISCVMCExpr::VK_RISCV_None;
   }
 
+  bool isUImm7Lsb000() const {
+    if (!isImm())
+      return false;
+    int64_t Imm;
+    RISCVMCExpr::VariantKind VK = RISCVMCExpr::VK_RISCV_None;
+    bool IsConstantImm = evaluateConstantImm(getImm(), Imm, VK);
+    return IsConstantImm && isShiftedUInt<4, 3>(Imm) &&
+           VK == RISCVMCExpr::VK_RISCV_None;
+  }
+
   bool isUImm8Lsb00() const {
     if (!isImm())
       return false;

llvm/lib/Target/RISCV/CMakeLists.txt

@@ -48,6 +48,7 @@ add_llvm_target(RISCVCodeGen
   RISCVISelLowering.cpp
   RISCVLandingPadSetup.cpp
   RISCVMachineFunctionInfo.cpp
+  RISCVLoadStoreOptimizer.cpp
   RISCVMergeBaseOffset.cpp
   RISCVOptWInstrs.cpp
   RISCVPostRAExpandPseudoInsts.cpp

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

@@ -308,6 +308,7 @@ enum OperandType : unsigned {
   OPERAND_UIMM6_LSB0,
   OPERAND_UIMM7,
   OPERAND_UIMM7_LSB00,
+  OPERAND_UIMM7_LSB000,
   OPERAND_UIMM8_LSB00,
   OPERAND_UIMM8,
   OPERAND_UIMM8_LSB000,

llvm/lib/Target/RISCV/RISCV.h

@@ -84,6 +84,8 @@ void initializeRISCVMoveMergePass(PassRegistry &);
 
 FunctionPass *createRISCVPushPopOptimizationPass();
 void initializeRISCVPushPopOptPass(PassRegistry &);
+FunctionPass *createRISCVLoadStoreOptPass();
+void initializeRISCVLoadStoreOptPass(PassRegistry &);
 
 FunctionPass *createRISCVZacasABIFixPass();
 void initializeRISCVZacasABIFixPass(PassRegistry &);

llvm/lib/Target/RISCV/RISCVFeatures.td

@@ -1423,6 +1423,19 @@ def NoConditionalMoveFusion  : Predicate<"!Subtarget->hasConditionalMoveFusion()
 def TuneMIPSP8700
     : SubtargetFeature<"mips-p8700", "RISCVProcFamily", "MIPSP8700",
                        "MIPS p8700 processor">;
+def FeatureVendorMIPSCMove : SubtargetFeature<"xmipscmove", "HasVendorMIPSCMove",
+                                       "true", "Using CCMov",
+                                       [Feature64Bit]>;
+def HasVendorMIPSCMove
+    : Predicate<"Subtarget->useCCMovInsn()">,
+      AssemblerPredicate<(all_of FeatureVendorMIPSCMove), "'ccmov' instruction">;
+def FeatureVendorMIPSLoadStorePairs
+    : SubtargetFeature<"xmipslsp", "HasMIPSLSP", "true",
+                       "Optimize for hardware load-store bonding">;
+def HasVendorMIPSLoadStorePairs
+    : Predicate<"Subtarget->useLoadStorePairs()">,
+      AssemblerPredicate<(all_of FeatureVendorMIPSLoadStorePairs),
+                         "load and store pair instructions">;
 
 def TuneSiFive7 : SubtargetFeature<"sifive7", "RISCVProcFamily", "SiFive7",
                                    "SiFive 7-Series processors">;

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -409,7 +409,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
     setOperationAction(ISD::ABS, MVT::i32, Custom);
   }
 
-  if (!Subtarget.hasVendorXTHeadCondMov())
+  if (Subtarget.hasVendorMIPSCMove())
+    setOperationAction(ISD::SELECT, XLenVT, Legal);
+  else if (!Subtarget.hasVendorXTHeadCondMov())
     setOperationAction(ISD::SELECT, XLenVT, Custom);
 
   static const unsigned FPLegalNodeTypes[] = {

llvm/lib/Target/RISCV/RISCVInstrFormats.td

@@ -514,6 +514,78 @@ class RVInstJ<RISCVOpcode opcode, dag outs, dag ins, string opcodestr,
   let Inst{6-0} = opcode.Value;
 }
 
+//===----------------------------------------------------------------------===//
+// MIPS custom instruction formats
+//===----------------------------------------------------------------------===//
+
+// Load double pair format.
+class LDPFormat<dag outs, dag ins, string opcodestr, string argstr>
+    : RVInst<outs, ins, opcodestr, argstr, [], InstFormatI> {
+  bits<7> imm7;
+  bits<5> rs1;
+  bits<5> rd1;
+  bits<5> rd2;
+
+  let Inst{31-27} = rd2;
+  let Inst{26-23} = imm7{6-3};
+  let Inst{22-20} = 0b000;
+  let Inst{19-15} = rs1;
+  let Inst{14-12} = 0b100;
+  let Inst{11-7} = rd1;
+  let Inst{6-0} = 0b0001011;
+}
+
+// Load word pair format.
+class LWPFormat<dag outs, dag ins, string opcodestr, string argstr>
+    : RVInst<outs, ins, opcodestr, argstr, [], InstFormatI> {
+  bits<7> imm7;
+  bits<5> rs1;
+  bits<5> rd1;
+  bits<5> rd2;
+
+  let Inst{31-27} = rd2;
+  let Inst{26-22} = imm7{6-2};
+  let Inst{21-20} = 0b01;
+  let Inst{19-15} = rs1;
+  let Inst{14-12} = 0b100;
+  let Inst{11-7} = rd1;
+  let Inst{6-0} = 0b0001011;
+}
+
+// Store double pair format.
+class SDPFormat<dag outs, dag ins, string opcodestr, string argstr>
+    : RVInst<outs, ins, opcodestr, argstr, [], InstFormatI> {
+  bits<7> imm7;
+  bits<5> rs3;
+  bits<5> rs2;
+  bits<5> rs1;
+
+  let Inst{31-27} = rs3;
+  let Inst{26-25} = imm7{6-5};
+  let Inst{24-20} = rs2;
+  let Inst{19-15} = rs1;
+  let Inst{14-12} = 0b101;
+  let Inst{11-10} = imm7{4-3};
+  let Inst{9-0} = 0b0000001011;
+}
+
+// Store word pair format.
+class SWPFormat<dag outs, dag ins, string opcodestr, string argstr>
+    : RVInst<outs, ins, opcodestr, argstr, [], InstFormatI> {
+  bits<7> imm7;
+  bits<5> rs3;
+  bits<5> rs2;
+  bits<5> rs1;
+
+  let Inst{31-27} = rs3;
+  let Inst{26-25} = imm7{6-5};
+  let Inst{24-20} = rs2;
+  let Inst{19-15} = rs1;
+  let Inst{14-12} = 0b101;
+  let Inst{11-9} = imm7{4-2};
+  let Inst{8-0} = 0b010001011;
+}
+
 //===----------------------------------------------------------------------===//
 // Instruction classes for .insn directives
 //===----------------------------------------------------------------------===//

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -2489,6 +2489,9 @@ bool RISCVInstrInfo::verifyInstruction(const MachineInstr &MI,
         case RISCVOp::OPERAND_UIMM7_LSB00:
           Ok = isShiftedUInt<5, 2>(Imm);
           break;
+        case RISCVOp::OPERAND_UIMM7_LSB000:
+          Ok = isShiftedUInt<4, 3>(Imm);
+          break;
         case RISCVOp::OPERAND_UIMM8_LSB00:
           Ok = isShiftedUInt<6, 2>(Imm);
           break;
@@ -2735,6 +2738,46 @@ MachineInstr *RISCVInstrInfo::emitLdStWithAddr(MachineInstr &MemI,
       .setMIFlags(MemI.getFlags());
 }
 
+bool RISCVInstrInfo::isPairableLdStInstOpc(unsigned Opc) {
+  switch (Opc) {
+  default:
+    return false;
+  case RISCV::SH:
+  case RISCV::LH:
+  case RISCV::LHU:
+  case RISCV::SW:
+  case RISCV::FSW:
+  case RISCV::LW:
+  case RISCV::FLW:
+  case RISCV::SD:
+  case RISCV::FSD:
+  case RISCV::LD:
+  case RISCV::FLD:
+    return true;
+  }
+}
+
+bool RISCVInstrInfo::isLdStSafeToPair(const MachineInstr &LdSt,
+                                      const TargetRegisterInfo *TRI) {
+  // If this is a volatile load/store, don't mess with it.
+  if (LdSt.hasOrderedMemoryRef() || LdSt.getNumExplicitOperands() != 3)
+    return false;
+
+  if (LdSt.getOperand(1).isFI())
+    return true;
+
+  assert(LdSt.getOperand(1).isReg() && "Expected a reg operand.");
+  // Can't cluster if the instruction modifies the base register
+  // or it is update form. e.g. ld x5,8(x5)
+  if (LdSt.modifiesRegister(LdSt.getOperand(1).getReg(), TRI))
+    return false;
+
+  if (!LdSt.getOperand(2).isImm())
+    return false;
+
+  return true;
+}
+
 bool RISCVInstrInfo::getMemOperandsWithOffsetWidth(
     const MachineInstr &LdSt, SmallVectorImpl<const MachineOperand *> &BaseOps,
     int64_t &Offset, bool &OffsetIsScalable, LocationSize &Width,

llvm/lib/Target/RISCV/RISCVInstrInfo.h

@@ -301,6 +301,12 @@ class RISCVInstrInfo : public RISCVGenInstrInfo {
   std::unique_ptr<TargetInstrInfo::PipelinerLoopInfo>
   analyzeLoopForPipelining(MachineBasicBlock *LoopBB) const override;
 
+  /// Return true if pairing the given load or store may be paired with another.
+  static bool isPairableLdStInstOpc(unsigned Opc);
+
+  static bool isLdStSafeToPair(const MachineInstr &LdSt,
+                               const TargetRegisterInfo *TRI);
+
 protected:
   const RISCVSubtarget &STI;