[Arm][AArch64] Add support for v8.9-A/v9.4-A base extensions

This implements the base extensions that are part of the v8.9-A and
v9.4-A architecture versions, including:

* The Clear BHB Instruction (FEAT_CLRBHB)
* The Speculation Restriction Instruction (FEAT_SPECRES2)
* The SLC target for the PRFM instruction
* New system registers:
  * ID_AA64PFR2_EL1
  * ID_AA64MMFR3_EL1
  * HFGITR2_EL2
  * SCTLR2_EL3

More information on the new extensions can be found on:

* https://community.arm.com/arm-community-blogs/b/architectures-and-processors-blog/posts/arm-a-profile-architecture-2022
* https://developer.arm.com/downloads/-/exploration-tools

Contributors: Sam Elliott, Tomas Matheson and Son Tuan Vu.

Reviewed By: lenary

Differential Revision: https://reviews.llvm.org/D139424

Author: pratlucas

llvm/include/llvm/Support/AArch64TargetParser.def

@@ -151,6 +151,7 @@ AARCH64_ARCH_EXT_NAME("sme2p1",       AArch64::AEK_SME2p1,      "+sme2p1",
 AARCH64_ARCH_EXT_NAME("hbc",          AArch64::AEK_HBC,         "+hbc",          "-hbc")
 AARCH64_ARCH_EXT_NAME("mops",         AArch64::AEK_MOPS,        "+mops",         "-mops")
 AARCH64_ARCH_EXT_NAME("pmuv3",        AArch64::AEK_PERFMON,     "+perfmon",      "-perfmon")
+AARCH64_ARCH_EXT_NAME("predres2",     AArch64::AEK_SPECRES2,    "+specres2",     "-specres2")
 AARCH64_ARCH_EXT_NAME("cssc",         AArch64::AEK_CSSC,        "+cssc",         "-cssc")
 AARCH64_ARCH_EXT_NAME("rcpc3",        AArch64::AEK_RCPC3,       "+rcpc3",        "-rcpc3")
 AARCH64_ARCH_EXT_NAME("the",          AArch64::AEK_THE,         "+the",          "-the")

llvm/include/llvm/Support/AArch64TargetParser.h

@@ -82,6 +82,7 @@ enum ArchExtKind : uint64_t {
   AEK_THE =         1ULL << 50, // FEAT_THE
   AEK_D128 =        1ULL << 51, // FEAT_D128
   AEK_LSE128 =      1ULL << 52, // FEAT_LSE128
+  AEK_SPECRES2 =    1ULL << 53, // FEAT_SPECRES2
 };
 // clang-format on
 

llvm/lib/Target/AArch64/AArch64.td

@@ -508,6 +508,16 @@ def FeatureNoBTIAtReturnTwice : SubtargetFeature<"no-bti-at-return-twice",
                                                  "Don't place a BTI instruction "
                                                  "after a return-twice">;
 
+def FeatureCLRBHB : SubtargetFeature<"clrbhb", "HasCLRBHB",
+    "true", "Enable Clear BHB instruction (FEAT_CLRBHB)">;
+
+def FeaturePRFM_SLC : SubtargetFeature<"prfm-slc-target", "HasPRFM_SLC",
+    "true", "Enable SLC target for PRFM instruction">;
+
+def FeatureSPECRES2 : SubtargetFeature<"specres2", "HasSPECRES2",
+    "true", "Enable Speculation Restriction Instruction (FEAT_SPECRES2)",
+    [FeaturePredRes]>;
+
 def FeatureMEC : SubtargetFeature<"mec", "HasMEC",
     "true", "Enable Memory Encryption Contexts Extension", [FeatureRME]>;
 
@@ -578,7 +588,8 @@ def HasV8_8aOps : SubtargetFeature<
 
 def HasV8_9aOps : SubtargetFeature<
   "v8.9a", "HasV8_9aOps", "true", "Support ARM v8.9a instructions",
-  [HasV8_8aOps, FeatureCSSC]>;
+  [HasV8_8aOps, FeatureCLRBHB, FeaturePRFM_SLC, FeatureSPECRES2,
+   FeatureCSSC]>;
 
 def HasV9_0aOps : SubtargetFeature<
   "v9a", "HasV9_0aOps", "true", "Support ARM v9a instructions",

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -233,6 +233,10 @@ def HasHBC           : Predicate<"Subtarget->hasHBC()">,
                        AssemblerPredicateWithAll<(all_of FeatureHBC), "hbc">;
 def HasMOPS          : Predicate<"Subtarget->hasMOPS()">,
                        AssemblerPredicateWithAll<(all_of FeatureMOPS), "mops">;
+def HasCLRBHB        : Predicate<"Subtarget->hasCLRBHB()">,
+                       AssemblerPredicateWithAll<(all_of FeatureCLRBHB), "clrbhb">;
+def HasSPECRES2      : Predicate<"Subtarget->hasSPECRES2()">,
+                       AssemblerPredicateWithAll<(all_of FeatureSPECRES2), "specres2">;
 def HasITE           : Predicate<"Subtarget->hasITE()">,
                        AssemblerPredicateWithAll<(all_of FeatureITE), "ite">;
 def HasTHE           : Predicate<"Subtarget->hasTHE()">,
@@ -8546,6 +8550,11 @@ def : Pat<(AArch64AssertZExtBool GPR32:$op),
 //===----------------------------===//
 // 2022 Architecture Extensions:
 //===----------------------------===//
+def : InstAlias<"clrbhb",  (HINT 22), 0>;
+let Predicates = [HasCLRBHB] in {
+  def : InstAlias<"clrbhb",  (HINT 22), 1>;
+}
+
 defm RCW     : ReadCheckWriteCompareAndSwap;
 
 defm RCWCLR  : ReadCheckWriteOperation<0b001, "clr">;

llvm/lib/Target/AArch64/AArch64SystemOperands.td

@@ -230,33 +230,51 @@ def : TSB<"csync", 0>;
 // PRFM (prefetch) instruction options.
 //===----------------------------------------------------------------------===//
 
-class PRFM<string name, bits<5> encoding> : SearchableTable {
+class PRFM<string type,   bits<2> type_encoding,
+           string target, bits<2> target_encoding,
+           string policy, bits<1> policy_encoding> : SearchableTable {
   let SearchableFields = ["Name", "Encoding"];
   let EnumValueField = "Encoding";
 
-  string Name = name;
+  string Name = type # target # policy;
   bits<5> Encoding;
-  let Encoding = encoding;
+  let Encoding{4-3} = type_encoding;
+  let Encoding{2-1} = target_encoding;
+  let Encoding{0} = policy_encoding;
+
+  code Requires = [{ {} }];
 }
 
-def : PRFM<"pldl1keep", 0x00>;
-def : PRFM<"pldl1strm", 0x01>;
-def : PRFM<"pldl2keep", 0x02>;
-def : PRFM<"pldl2strm", 0x03>;
-def : PRFM<"pldl3keep", 0x04>;
-def : PRFM<"pldl3strm", 0x05>;
-def : PRFM<"plil1keep", 0x08>;
-def : PRFM<"plil1strm", 0x09>;
-def : PRFM<"plil2keep", 0x0a>;
-def : PRFM<"plil2strm", 0x0b>;
-def : PRFM<"plil3keep", 0x0c>;
-def : PRFM<"plil3strm", 0x0d>;
-def : PRFM<"pstl1keep", 0x10>;
-def : PRFM<"pstl1strm", 0x11>;
-def : PRFM<"pstl2keep", 0x12>;
-def : PRFM<"pstl2strm", 0x13>;
-def : PRFM<"pstl3keep", 0x14>;
-def : PRFM<"pstl3strm", 0x15>;
+def : PRFM<"pld", 0b00, "l1",  0b00, "keep", 0b0>;
+def : PRFM<"pld", 0b00, "l1",  0b00, "strm", 0b1>;
+def : PRFM<"pld", 0b00, "l2",  0b01, "keep", 0b0>;
+def : PRFM<"pld", 0b00, "l2",  0b01, "strm", 0b1>;
+def : PRFM<"pld", 0b00, "l3",  0b10, "keep", 0b0>;
+def : PRFM<"pld", 0b00, "l3",  0b10, "strm", 0b1>;
+let Requires = [{ {AArch64::FeaturePRFM_SLC} }] in {
+def : PRFM<"pld", 0b00, "slc", 0b11, "keep", 0b0>;
+def : PRFM<"pld", 0b00, "slc", 0b11, "strm", 0b1>;
+}
+def : PRFM<"pli", 0b01, "l1",  0b00, "keep", 0b0>;
+def : PRFM<"pli", 0b01, "l1",  0b00, "strm", 0b1>;
+def : PRFM<"pli", 0b01, "l2",  0b01, "keep", 0b0>;
+def : PRFM<"pli", 0b01, "l2",  0b01, "strm", 0b1>;
+def : PRFM<"pli", 0b01, "l3",  0b10, "keep", 0b0>;
+def : PRFM<"pli", 0b01, "l3",  0b10, "strm", 0b1>;
+let Requires = [{ {AArch64::FeaturePRFM_SLC} }] in {
+def : PRFM<"pli", 0b01, "slc", 0b11, "keep", 0b0>;
+def : PRFM<"pli", 0b01, "slc", 0b11, "strm", 0b1>;
+}
+def : PRFM<"pst", 0b10, "l1",  0b00, "keep", 0b0>;
+def : PRFM<"pst", 0b10, "l1",  0b00, "strm", 0b1>;
+def : PRFM<"pst", 0b10, "l2",  0b01, "keep", 0b0>;
+def : PRFM<"pst", 0b10, "l2",  0b01, "strm", 0b1>;
+def : PRFM<"pst", 0b10, "l3",  0b10, "keep", 0b0>;
+def : PRFM<"pst", 0b10, "l3",  0b10, "strm", 0b1>;
+let Requires = [{ {AArch64::FeaturePRFM_SLC} }] in {
+def : PRFM<"pst", 0b10, "slc", 0b11, "keep", 0b0>;
+def : PRFM<"pst", 0b10, "slc", 0b11, "strm", 0b1>;
+}
 
 //===----------------------------------------------------------------------===//
 // SVE Prefetch instruction options.
@@ -600,23 +618,6 @@ defm : TLBI<"PAALLOS",      0b110, 0b1000, 0b0001, 0b100, 0>;
 defm : TLBI<"PAALL",        0b110, 0b1000, 0b0111, 0b100, 0>;
 }
 
-// Armv8.5-A Prediction Restriction by Context instruction options:
-class PRCTX<string name, bits<4> crm> : SearchableTable {
-  let SearchableFields = ["Name", "Encoding"];
-  let EnumValueField = "Encoding";
-
-  string Name = name;
-  bits<11> Encoding;
-  let Encoding{10-4} = 0b0110111;
-  let Encoding{3-0} = crm;
-  bit NeedsReg = 1;
-  code Requires = [{ {} }];
-}
-
-let Requires = [{ {AArch64::FeaturePredRes} }] in {
-def : PRCTX<"RCTX", 0b0011>;
-}
-
 //===----------------------------------------------------------------------===//
 // MRS/MSR (system register read/write) instruction options.
 //===----------------------------------------------------------------------===//
@@ -709,6 +710,7 @@ def : ROSysReg<"ID_ISAR6_EL1",       0b11, 0b000, 0b0000, 0b0010, 0b111> {
 }
 def : ROSysReg<"ID_AA64PFR0_EL1",     0b11, 0b000, 0b0000, 0b0100, 0b000>;
 def : ROSysReg<"ID_AA64PFR1_EL1",     0b11, 0b000, 0b0000, 0b0100, 0b001>;
+def : ROSysReg<"ID_AA64PFR2_EL1",     0b11, 0b000, 0b0000, 0b0100, 0b010>;
 def : ROSysReg<"ID_AA64DFR0_EL1",     0b11, 0b000, 0b0000, 0b0101, 0b000>;
 def : ROSysReg<"ID_AA64DFR1_EL1",     0b11, 0b000, 0b0000, 0b0101, 0b001>;
 def : ROSysReg<"ID_AA64AFR0_EL1",     0b11, 0b000, 0b0000, 0b0101, 0b100>;
@@ -719,20 +721,21 @@ def : ROSysReg<"ID_AA64ISAR2_EL1",    0b11, 0b000, 0b0000, 0b0110, 0b010>;
 def : ROSysReg<"ID_AA64MMFR0_EL1",    0b11, 0b000, 0b0000, 0b0111, 0b000>;
 def : ROSysReg<"ID_AA64MMFR1_EL1",    0b11, 0b000, 0b0000, 0b0111, 0b001>;
 def : ROSysReg<"ID_AA64MMFR2_EL1",    0b11, 0b000, 0b0000, 0b0111, 0b010>;
-def : ROSysReg<"MVFR0_EL1",          0b11, 0b000, 0b0000, 0b0011, 0b000>;
-def : ROSysReg<"MVFR1_EL1",          0b11, 0b000, 0b0000, 0b0011, 0b001>;
-def : ROSysReg<"MVFR2_EL1",          0b11, 0b000, 0b0000, 0b0011, 0b010>;
-def : ROSysReg<"RVBAR_EL1",          0b11, 0b000, 0b1100, 0b0000, 0b001>;
-def : ROSysReg<"RVBAR_EL2",          0b11, 0b100, 0b1100, 0b0000, 0b001>;
-def : ROSysReg<"RVBAR_EL3",          0b11, 0b110, 0b1100, 0b0000, 0b001>;
-def : ROSysReg<"ISR_EL1",            0b11, 0b000, 0b1100, 0b0001, 0b000>;
-def : ROSysReg<"CNTPCT_EL0",         0b11, 0b011, 0b1110, 0b0000, 0b001>;
-def : ROSysReg<"CNTVCT_EL0",         0b11, 0b011, 0b1110, 0b0000, 0b010>;
-def : ROSysReg<"ID_MMFR4_EL1",       0b11, 0b000, 0b0000, 0b0010, 0b110>;
-def : ROSysReg<"ID_MMFR5_EL1",       0b11, 0b000, 0b0000, 0b0011, 0b110>;
+def : ROSysReg<"ID_AA64MMFR3_EL1",    0b11, 0b000, 0b0000, 0b0111, 0b011>;
+def : ROSysReg<"MVFR0_EL1",           0b11, 0b000, 0b0000, 0b0011, 0b000>;
+def : ROSysReg<"MVFR1_EL1",           0b11, 0b000, 0b0000, 0b0011, 0b001>;
+def : ROSysReg<"MVFR2_EL1",           0b11, 0b000, 0b0000, 0b0011, 0b010>;
+def : ROSysReg<"RVBAR_EL1",           0b11, 0b000, 0b1100, 0b0000, 0b001>;
+def : ROSysReg<"RVBAR_EL2",           0b11, 0b100, 0b1100, 0b0000, 0b001>;
+def : ROSysReg<"RVBAR_EL3",           0b11, 0b110, 0b1100, 0b0000, 0b001>;
+def : ROSysReg<"ISR_EL1",             0b11, 0b000, 0b1100, 0b0001, 0b000>;
+def : ROSysReg<"CNTPCT_EL0",          0b11, 0b011, 0b1110, 0b0000, 0b001>;
+def : ROSysReg<"CNTVCT_EL0",          0b11, 0b011, 0b1110, 0b0000, 0b010>;
+def : ROSysReg<"ID_MMFR4_EL1",        0b11, 0b000, 0b0000, 0b0010, 0b110>;
+def : ROSysReg<"ID_MMFR5_EL1",        0b11, 0b000, 0b0000, 0b0011, 0b110>;
 
 // Trace registers
-//                                 Op0    Op1     CRn     CRm    Op2
+//                                   Op0    Op1     CRn     CRm    Op2
 def : ROSysReg<"TRCSTATR",           0b10, 0b001, 0b0000, 0b0011, 0b000>;
 def : ROSysReg<"TRCIDR8",            0b10, 0b001, 0b0000, 0b0000, 0b110>;
 def : ROSysReg<"TRCIDR9",            0b10, 0b001, 0b0000, 0b0001, 0b110>;
@@ -1662,6 +1665,7 @@ def : RWSysReg<"HDFGRTR2_EL2",     0b11, 0b100, 0b0011, 0b0001, 0b000>;
 def : RWSysReg<"HDFGWTR2_EL2",     0b11, 0b100, 0b0011, 0b0001, 0b001>;
 def : RWSysReg<"HFGRTR2_EL2",      0b11, 0b100, 0b0011, 0b0001, 0b010>;
 def : RWSysReg<"HFGWTR2_EL2",      0b11, 0b100, 0b0011, 0b0001, 0b011>;
+def : RWSysReg<"HFGITR2_EL2",      0b11, 0b100, 0b0011, 0b0001, 0b111>;
 }
 
 // v8.6a Enhanced Counter Virtualization
@@ -1768,6 +1772,7 @@ def : RWSysReg<"S2POR_EL1",   0b11, 0b000, 0b1010, 0b0010, 0b101>;
 def : RWSysReg<"SCTLR2_EL1",  0b11, 0b000, 0b0001, 0b0000, 0b011>;
 def : RWSysReg<"SCTLR2_EL12", 0b11, 0b101, 0b0001, 0b0000, 0b011>;
 def : RWSysReg<"SCTLR2_EL2",  0b11, 0b100, 0b0001, 0b0000, 0b011>;
+def : RWSysReg<"SCTLR2_EL3",  0b11, 0b110, 0b0001, 0b0000, 0b011>;
 
 // v8.9a/v9.4a Extension to Translation Control Registers (FEAT_TCR2)
 //                            Op0   Op1    CRn     CRm     Op2

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -3639,6 +3639,7 @@ static const struct Extension {
     {"ras", {AArch64::FeatureRAS}},
     {"lse", {AArch64::FeatureLSE}},
     {"predres", {AArch64::FeaturePredRes}},
+    {"predres2", {AArch64::FeatureSPECRES2}},
     {"ccdp", {AArch64::FeatureCacheDeepPersist}},
     {"mte", {AArch64::FeatureMTE}},
     {"memtag", {AArch64::FeatureMTE}},
@@ -3797,23 +3798,31 @@ bool AArch64AsmParser::parseSysAlias(StringRef Name, SMLoc NameLoc,
       return TokError(Str);
     }
     createSysAlias(TLBI->Encoding, Operands, S);
-  } else if (Mnemonic == "cfp" || Mnemonic == "dvp" || Mnemonic == "cpp") {
-    const AArch64PRCTX::PRCTX *PRCTX = AArch64PRCTX::lookupPRCTXByName(Op);
-    if (!PRCTX)
+  } else if (Mnemonic == "cfp" || Mnemonic == "dvp" || Mnemonic == "cpp" || Mnemonic == "cosp") {
+
+    if (Op.lower() != "rctx")
       return TokError("invalid operand for prediction restriction instruction");
-    else if (!PRCTX->haveFeatures(getSTI().getFeatureBits())) {
-      std::string Str(
-          Mnemonic.upper() + std::string(PRCTX->Name) + " requires: ");
-      setRequiredFeatureString(PRCTX->getRequiredFeatures(), Str);
-      return TokError(Str);
-    }
-    uint16_t PRCTX_Op2 =
-      Mnemonic == "cfp" ? 4 :
-      Mnemonic == "dvp" ? 5 :
-      Mnemonic == "cpp" ? 7 :
-      0;
-    assert(PRCTX_Op2 && "Invalid mnemonic for prediction restriction instruction");
-    createSysAlias(PRCTX->Encoding << 3 | PRCTX_Op2 , Operands, S);
+
+    bool hasAll = getSTI().hasFeature(AArch64::FeatureAll);
+    bool hasPredres = hasAll || getSTI().hasFeature(AArch64::FeaturePredRes);
+    bool hasSpecres2 = hasAll || getSTI().hasFeature(AArch64::FeatureSPECRES2);
+
+    if (Mnemonic == "cosp" && !hasSpecres2)
+      return TokError("COSP requires: predres2");
+    if (!hasPredres)
+      return TokError(Mnemonic.upper() + "RCTX requires: predres");
+
+    uint16_t PRCTX_Op2 = Mnemonic == "cfp"    ? 0b100
+                         : Mnemonic == "dvp"  ? 0b101
+                         : Mnemonic == "cosp" ? 0b110
+                         : Mnemonic == "cpp"  ? 0b111
+                                              : 0;
+    assert(PRCTX_Op2 &&
+           "Invalid mnemonic for prediction restriction instruction");
+    const auto SYS_3_7_3 = 0b01101110011; // op=3, CRn=7, CRm=3
+    const auto Encoding = SYS_3_7_3 << 3 | PRCTX_Op2;
+
+    createSysAlias(Encoding, Operands, S);
   }
 
   Lex(); // Eat operand.
@@ -5080,7 +5089,7 @@ bool AArch64AsmParser::ParseInstruction(ParseInstructionInfo &Info,
   // IC, DC, AT, TLBI and Prediction invalidation instructions are aliases for
   // the SYS instruction.
   if (Head == "ic" || Head == "dc" || Head == "at" || Head == "tlbi" ||
-      Head == "cfp" || Head == "dvp" || Head == "cpp")
+      Head == "cfp" || Head == "dvp" || Head == "cpp" || Head == "cosp")
     return parseSysAlias(Head, NameLoc, Operands);
 
   // TLBIP instructions are aliases for the SYSP instruction.

llvm/lib/Target/AArch64/MCTargetDesc/AArch64InstPrinter.cpp

@@ -910,18 +910,23 @@ bool AArch64InstPrinter::printSysAlias(const MCInst *MI,
     // Prediction Restriction aliases
     case 3: {
       Search_PRCTX:
-      const AArch64PRCTX::PRCTX *PRCTX = AArch64PRCTX::lookupPRCTXByEncoding(Encoding >> 3);
-      if (!PRCTX || !PRCTX->haveFeatures(STI.getFeatureBits()))
+      if (Op1Val != 3 || CnVal != 7 || CmVal != 3)
         return false;
 
-      NeedsReg = PRCTX->NeedsReg;
+      const auto Requires =
+          Op2Val == 6 ? AArch64::FeatureSPECRES2 : AArch64::FeaturePredRes;
+      if (!(STI.hasFeature(AArch64::FeatureAll) || STI.hasFeature(Requires)))
+        return false;
+
+      NeedsReg = true;
       switch (Op2Val) {
       default: return false;
       case 4: Ins = "cfp\t"; break;
       case 5: Ins = "dvp\t"; break;
+      case 6: Ins = "cosp\t"; break;
       case 7: Ins = "cpp\t"; break;
       }
-      Name = std::string(PRCTX->Name);
+      Name = "RCTX";
     }
     break;
     // IC aliases
@@ -1433,9 +1438,12 @@ void AArch64InstPrinter::printPrefetchOp(const MCInst *MI, unsigned OpNum,
       O << PRFM->Name;
       return;
     }
-  } else if (auto PRFM = AArch64PRFM::lookupPRFMByEncoding(prfop)) {
-    O << PRFM->Name;
-    return;
+  } else {
+    auto PRFM = AArch64PRFM::lookupPRFMByEncoding(prfop);
+    if (PRFM && PRFM->haveFeatures(STI.getFeatureBits())) {
+      O << PRFM->Name;
+      return;
+    }
   }
 
   O << markup("<imm:") << '#' << formatImm(prfop) << markup(">");

llvm/lib/Target/ARM/ARM.td

@@ -542,6 +542,11 @@ def FeatureNoBTIAtReturnTwice : SubtargetFeature<"no-bti-at-return-twice",
                                                  "Don't place a BTI instruction "
                                                  "after a return-twice">;
 
+// Armv8.9-A/Armv9.4-A 2022 Architecture Extensions
+def FeatureCLRBHB : SubtargetFeature<"clrbhb", "HasCLRBHB", "true",
+                                     "Enable Clear BHB instruction">;
+
+
 def FeatureFixCortexA57AES1742098 : SubtargetFeature<"fix-cortex-a57-aes-1742098",
   "FixCortexA57AES1742098", "true",
   "Work around Cortex-A57 Erratum 1742098 / Cortex-A72 Erratum 1655431 (AES)">;
@@ -674,7 +679,7 @@ def HasV8_8aOps   : SubtargetFeature<"v8.8a", "HasV8_8aOps", "true",
 
 def HasV8_9aOps   : SubtargetFeature<"v8.9a", "HasV8_9aOps", "true",
                                    "Support ARM v8.9a instructions",
-                                   [HasV8_8aOps]>;
+                                   [HasV8_8aOps, FeatureCLRBHB]>;
 
 def HasV9_0aOps   : SubtargetFeature<"v9a", "HasV9_0aOps", "true",
                                    "Support ARM v9a instructions",

llvm/lib/Target/ARM/ARMInstrInfo.td

@@ -2189,6 +2189,10 @@ def : InstAlias<"sevl$p", (HINT 5, pred:$p)>, Requires<[IsARM, HasV8]>;
 def : InstAlias<"esb$p", (HINT 16, pred:$p)>, Requires<[IsARM, HasRAS]>;
 def : InstAlias<"csdb$p", (HINT 20, pred:$p)>, Requires<[IsARM, HasV6K]>;
 
+// Clear BHB instruction
+def : InstAlias<"clrbhb$p", (HINT 22, pred:$p), 0>, Requires<[IsARM, HasV8]>;
+def : InstAlias<"clrbhb$p", (HINT 22, pred:$p), 1>, Requires<[IsARM, HasV8, HasCLRBHB]>;
+
 def SEL : AI<(outs GPR:$Rd), (ins GPR:$Rn, GPR:$Rm), DPFrm, NoItinerary, "sel",
              "\t$Rd, $Rn, $Rm",
              [(set GPR:$Rd, (int_arm_sel GPR:$Rn, GPR:$Rm))]>,

llvm/lib/Target/ARM/ARMInstrThumb2.td

@@ -4089,6 +4089,10 @@ def : t2InstAlias<"bti$p", (t2HINT 15, pred:$p), 1>;
 def : t2InstAlias<"pac$p r12,lr,sp", (t2HINT 29, pred:$p), 1>;
 def : t2InstAlias<"aut$p r12,lr,sp", (t2HINT 45, pred:$p), 1>;
 
+// Clear BHB instruction
+def : InstAlias<"clrbhb$p", (t2HINT 22, pred:$p), 0>, Requires<[IsThumb2, HasV8]>;
+def : InstAlias<"clrbhb$p", (t2HINT 22, pred:$p), 1>, Requires<[IsThumb2, HasV8, HasCLRBHB]>;
+
 def t2DBG : T2I<(outs), (ins imm0_15:$opt), NoItinerary, "dbg", "\t$opt",
                 [(int_arm_dbg imm0_15:$opt)]> {
   bits<4> opt;

llvm/lib/Target/ARM/ARMPredicates.td

@@ -226,3 +226,7 @@ def GenExecuteOnly : Predicate<"Subtarget->genExecuteOnly()">;
 // Armv8.5-A extensions
 def HasSB            : Predicate<"Subtarget->hasSB()">,
                        AssemblerPredicate<(all_of FeatureSB), "sb">;
+
+// Armv8.9-A/9.4-A 2022 Architecture extensions
+def HasCLRBHB        : Predicate<"Subtarget->hasCLRBHB()">,
+                       AssemblerPredicate<(all_of FeatureCLRBHB), "clrbhb">;