diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.h b/llvm/lib/Target/RISCV/RISCVISelLowering.h
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.h
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.h
@@ -51,9 +51,19 @@
   FMV_X_ANYEXTW_RV64,
   // READ_CYCLE_WIDE - A read of the 64-bit cycle CSR on a 32-bit target
   // (returns (Lo, Hi)). It takes a chain operand.
-  READ_CYCLE_WIDE
+  READ_CYCLE_WIDE,
+  // Generalized Reverse and Generalized Or-Combine - directly matching the
+  // semantics of the named RISC-V instructions. Lowered as custom nodes as
+  // TableGen chokes when faced with commutative permutations in deeply-nested
+  // DAGs. Each node takes an input operand and a TargetConstant immediate
+  // shift amount, and outputs a bit-manipulated version of input. All operands
+  // are of type XLenVT.
+  GREVI,
+  GREVIW,
+  GORCI,
+  GORCIW,
 };
-}
+} // namespace RISCVISD
 
 class RISCVTargetLowering : public TargetLowering {
   const RISCVSubtarget &Subtarget;
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -259,6 +259,11 @@
 
   // We can use any register for comparisons
   setHasMultipleConditionRegisters();
+
+  if (Subtarget.hasStdExtZbp()) {
+    setTargetDAGCombine(ISD::OR);
+    setTargetDAGCombine(ISD::SIGN_EXTEND_INREG);
+  }
 }
 
 EVT RISCVTargetLowering::getSetCCResultType(const DataLayout &DL, LLVMContext &,
@@ -1031,6 +1036,153 @@
   }
 }
 
+// A structure to hold one of the bit-manipulation patterns below. Together, a
+// SHL and non-SHL pattern may form a bit-manipulation pair on a single source:
+//   (or (and (shl x, 1), 0xAAAAAAAA),
+//       (and (srl x, 1), 0x55555555))
+struct RISCVBitmanipPat {
+  SDValue Op;
+  unsigned ShAmt;
+  bool IsSHL;
+
+  bool formsPairWith(const RISCVBitmanipPat &Other) const {
+    return Op == Other.Op && ShAmt == Other.ShAmt && IsSHL != Other.IsSHL;
+  }
+};
+
+// Matches any of the following bit-manipulation patterns:
+//   (and (shl x, 1), (0x55555555 << 1))
+//   (and (srl x, 1), 0x55555555)
+//   (shl (and x, 0x55555555), 1)
+//   (srl (and x, (0x55555555 << 1)), 1)
+// where the shift amount and mask may vary thus:
+//   [1]  = 0x55555555 / 0xAAAAAAAA
+//   [2]  = 0x33333333 / 0xCCCCCCCC
+//   [4]  = 0x0F0F0F0F / 0xF0F0F0F0
+//   [8]  = 0x00FF00FF / 0xFF00FF00
+//   [16] = 0x0000FFFF / 0xFFFFFFFF
+//   [32] = 0x00000000FFFFFFFF / 0xFFFFFFFF00000000 (for RV64)
+static Optional<RISCVBitmanipPat> matchRISCVBitmanipPat(SDValue Op, bool IsW) {
+  Optional<uint64_t> Mask;
+  // Optionally consume a mask around the shift operation.
+  if (Op.getOpcode() == ISD::AND && isa<ConstantSDNode>(Op.getOperand(1))) {
+    Mask = Op.getConstantOperandVal(1);
+    Op = Op.getOperand(0);
+  }
+  if (Op.getOpcode() != ISD::SHL && Op.getOpcode() != ISD::SRL)
+    return None;
+  bool IsSHL = Op.getOpcode() == ISD::SHL;
+
+  if (!isa<ConstantSDNode>(Op.getOperand(1)))
+    return None;
+  auto ShAmt = Op.getConstantOperandVal(1);
+
+  if (!isPowerOf2_64(ShAmt))
+    return None;
+
+  // These are the unshifted masks which we use to match bit-manipulation
+  // patterns. They may be shifted left in certain circumstances.
+  static const uint64_t BitmanipMasks[] = {
+      0x5555555555555555ULL, 0x3333333333333333ULL, 0x0F0F0F0F0F0F0F0FULL,
+      0x00FF00FF00FF00FFULL, 0x0000FFFF0000FFFFULL, 0x00000000FFFFFFFFULL,
+  };
+
+  unsigned MaskIdx = Log2_64(ShAmt);
+  if (MaskIdx >= array_lengthof(BitmanipMasks))
+    return None;
+
+  auto Src = Op.getOperand(0);
+
+  // When matching the W forms, we only expect a 32-bit mask.
+  unsigned Width = Op.getValueType() == MVT::i64 && !IsW ? 64 : 32;
+  auto ExpMask = BitmanipMasks[MaskIdx] & maskTrailingOnes<uint64_t>(Width);
+
+  // The expected mask is shifted left when the AND is found around SHL
+  // patterns.
+  //   ((x >> 1) & 0x55555555)
+  //   ((x << 1) & 0xAAAAAAAA)
+  bool SHLExpMask = IsSHL;
+
+  if (!Mask) {
+    // Sometimes LLVM keeps the mask as an operand of the shift, typically when
+    // the mask is all ones: consume that now.
+    if (Src.getOpcode() == ISD::AND && isa<ConstantSDNode>(Src.getOperand(1))) {
+      Mask = Src.getConstantOperandVal(1);
+      Src = Src.getOperand(0);
+      // The expected mask is now in fact shifted left for SRL, so reverse the
+      // decision.
+      //   ((x & 0xAAAAAAAA) >> 1)
+      //   ((x & 0x55555555) << 1)
+      SHLExpMask = !SHLExpMask;
+    } else {
+      // Use a default shifted mask of all-ones if there's no AND, truncated
+      // down to the expected width. This simplifies the logic later on.
+      Mask = maskTrailingOnes<uint64_t>(Width);
+      *Mask &= (IsSHL ? *Mask << ShAmt : *Mask >> ShAmt);
+    }
+  }
+
+  if (SHLExpMask)
+    ExpMask <<= ShAmt;
+
+  if (Mask != ExpMask)
+    return None;
+
+  return RISCVBitmanipPat{Src, (unsigned)ShAmt, IsSHL};
+}
+
+// Match the following pattern as a GREVI(W) operation
+//   (or (BITMANIP_SHL x), (BITMANIP_SRL x))
+static SDValue combineORToGREV(SDValue Op, bool IsW, SelectionDAG &DAG,
+                               const RISCVSubtarget &Subtarget) {
+  if (Op.getSimpleValueType() == Subtarget.getXLenVT()) {
+    auto LHS = matchRISCVBitmanipPat(Op.getOperand(0), IsW);
+    auto RHS = matchRISCVBitmanipPat(Op.getOperand(1), IsW);
+    if (LHS && RHS && LHS->formsPairWith(*RHS)) {
+      SDLoc DL(Op);
+      return DAG.getNode(
+          IsW ? RISCVISD::GREVIW : RISCVISD::GREVI, DL, Op.getValueType(),
+          LHS->Op,
+          DAG.getTargetConstant(LHS->ShAmt, DL, Subtarget.getXLenVT()));
+    }
+  }
+  return SDValue();
+}
+
+// Match the following pattern as a GORCI(W) operation
+//   (or (or (BITMANIP_SHL x), x),
+//       (BITMANIP_SRL x))
+static SDValue combineORToGORC(SDValue Op, bool IsW, SelectionDAG &DAG,
+                               const RISCVSubtarget &Subtarget) {
+  if (Op.getSimpleValueType() == Subtarget.getXLenVT()) {
+    SDValue Op0 = Op.getOperand(0);
+    SDValue Op1 = Op.getOperand(1);
+    // OR is commutable so canonicalize its OR operand to the left
+    if (Op0.getOpcode() != ISD::OR && Op1.getOpcode() == ISD::OR)
+      std::swap(Op0, Op1);
+    if (Op0.getOpcode() != ISD::OR)
+      return SDValue();
+    SDValue OrOp0 = Op0.getOperand(0);
+    SDValue OrOp1 = Op0.getOperand(1);
+    auto LHS = matchRISCVBitmanipPat(OrOp0, IsW);
+    // OR is commutable so swap the operands and try again: x might have been
+    // on the left
+    if (!LHS) {
+      std::swap(OrOp0, OrOp1);
+      LHS = matchRISCVBitmanipPat(OrOp0, IsW);
+    }
+    auto RHS = matchRISCVBitmanipPat(Op1, IsW);
+    if (LHS && RHS && LHS->formsPairWith(*RHS) && LHS->Op == OrOp1) {
+      SDLoc DL(Op);
+      return DAG.getNode(
+          IsW ? RISCVISD::GORCIW : RISCVISD::GORCI, DL, Op.getValueType(),
+          LHS->Op,
+          DAG.getTargetConstant(LHS->ShAmt, DL, Subtarget.getXLenVT()));
+    }
+  }
+  return SDValue();
+}
+
 SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
                                                DAGCombinerInfo &DCI) const {
   SelectionDAG &DAG = DCI.DAG;
@@ -1126,6 +1278,26 @@
     return DAG.getNode(ISD::AND, DL, MVT::i64, NewFMV,
                        DAG.getConstant(~SignBit, DL, MVT::i64));
   }
+  case ISD::OR:
+    if (auto GREV = combineORToGREV(SDValue(N, 0),
+                                    /*IsW*/ false, DCI.DAG, Subtarget))
+      return GREV;
+    if (auto GORC = combineORToGORC(SDValue(N, 0),
+                                    /*IsW*/ false, DCI.DAG, Subtarget))
+      return GORC;
+    break;
+  case ISD::SIGN_EXTEND_INREG:
+    if (Subtarget.is64Bit() &&
+        cast<VTSDNode>(N->getOperand(1))->getVT() == MVT::i32 &&
+        N->getOperand(0).getOpcode() == ISD::OR) {
+      if (auto GREV = combineORToGREV(N->getOperand(0), /*IsW*/ true, DCI.DAG,
+                                      Subtarget))
+        return GREV;
+      if (auto GORC = combineORToGORC(N->getOperand(0), /*IsW*/ true, DCI.DAG,
+                                      Subtarget))
+        return GORC;
+    }
+    break;
   }
 
   return SDValue();
@@ -2641,6 +2813,14 @@
     return "RISCVISD::FMV_X_ANYEXTW_RV64";
   case RISCVISD::READ_CYCLE_WIDE:
     return "RISCVISD::READ_CYCLE_WIDE";
+  case RISCVISD::GREVI:
+    return "RISCVISD::GREVI";
+  case RISCVISD::GREVIW:
+    return "RISCVISD::GREVIW";
+  case RISCVISD::GORCI:
+    return "RISCVISD::GORCI";
+  case RISCVISD::GORCIW:
+    return "RISCVISD::GORCIW";
   }
   return nullptr;
 }
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoB.td b/llvm/lib/Target/RISCV/RISCVInstrInfoB.td
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoB.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoB.td
@@ -709,63 +709,20 @@
 def : Pat<(and (srl GPR:$rs1, uimmlog2xlen:$shamt), (XLenVT 1)),
           (SBEXTI GPR:$rs1, uimmlog2xlen:$shamt)>;
 
-let Predicates = [HasStdExtZbp, IsRV32] in {
-def : Pat<(or (or (and (srl GPR:$rs1, (i32 1)), (i32 0x55555555)), GPR:$rs1),
-              (and (shl GPR:$rs1, (i32 1)), (i32 0xAAAAAAAA))),
-          (GORCI GPR:$rs1, (i32 1))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i32 2)), (i32 0x33333333)), GPR:$rs1),
-              (and (shl GPR:$rs1, (i32 2)), (i32 0xCCCCCCCC))),
-          (GORCI GPR:$rs1, (i32 2))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i32 4)), (i32 0x0F0F0F0F)), GPR:$rs1),
-              (and (shl GPR:$rs1, (i32 4)), (i32 0xF0F0F0F0))),
-          (GORCI GPR:$rs1, (i32 4))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i32 8)), (i32 0x00FF00FF)), GPR:$rs1),
-              (and (shl GPR:$rs1, (i32 8)), (i32 0xFF00FF00))),
-          (GORCI GPR:$rs1, (i32 8))>;
-def : Pat<(or (or (srl GPR:$rs1, (i32 16)), GPR:$rs1),
-              (shl GPR:$rs1, (i32 16))),
-          (GORCI GPR:$rs1, (i32 16))>;
-} // Predicates = [HasStdExtZbp, IsRV32]
+def SDT_RISCVGREVGORC  : SDTypeProfile<1, 2, [SDTCisVT<0, XLenVT>,
+                                              SDTCisSameAs<0, 1>,
+                                              SDTCisSameAs<1, 2>]>;
+def riscv_grevi    : SDNode<"RISCVISD::GREVI", SDT_RISCVGREVGORC, []>;
+def riscv_greviw   : SDNode<"RISCVISD::GREVIW", SDT_RISCVGREVGORC, []>;
+def riscv_gorci    : SDNode<"RISCVISD::GORCI", SDT_RISCVGREVGORC, []>;
+def riscv_gorciw   : SDNode<"RISCVISD::GORCIW", SDT_RISCVGREVGORC, []>;
 
-let Predicates = [HasStdExtZbp, IsRV64] in {
-def : Pat<(or (or (and (srl GPR:$rs1, (i64 1)), (i64 0x5555555555555555)),
-                   GPR:$rs1),
-              (and (shl GPR:$rs1, (i64 1)), (i64 0xAAAAAAAAAAAAAAAA))),
-          (GORCI GPR:$rs1, (i64 1))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i64 2)), (i64 0x3333333333333333)),
-                   GPR:$rs1),
-              (and (shl GPR:$rs1, (i64 2)), (i64 0xCCCCCCCCCCCCCCCC))),
-          (GORCI GPR:$rs1, (i64 2))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i64 4)), (i64 0x0F0F0F0F0F0F0F0F)),
-                   GPR:$rs1),
-              (and (shl GPR:$rs1, (i64 4)), (i64 0xF0F0F0F0F0F0F0F0))),
-          (GORCI GPR:$rs1, (i64 4))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i64 8)), (i64 0x00FF00FF00FF00FF)),
-                   GPR:$rs1),
-              (and (shl GPR:$rs1, (i64 8)), (i64 0xFF00FF00FF00FF00))),
-          (GORCI GPR:$rs1, (i64 8))>;
-def : Pat<(or (or (and (srl GPR:$rs1, (i64 16)), (i64 0x0000FFFF0000FFFF)),
-                   GPR:$rs1),
-              (and (shl GPR:$rs1, (i64 16)), (i64 0xFFFF0000FFFF0000))),
-          (GORCI GPR:$rs1, (i64 16))>;
-def : Pat<(or (or (srl GPR:$rs1, (i64 32)), GPR:$rs1),
-              (shl GPR:$rs1, (i64 32))),
-          (GORCI GPR:$rs1, (i64 32))>;
-} // Predicates = [HasStdExtZbp, IsRV64]
+let Predicates = [HasStdExtZbp] in {
+def : Pat<(riscv_grevi GPR:$rs1, timm:$shamt), (GREVI GPR:$rs1, timm:$shamt)>;
+def : Pat<(riscv_gorci GPR:$rs1, timm:$shamt), (GORCI GPR:$rs1, timm:$shamt)>;
+} // Predicates = [HasStdExtZbp]
 
 let Predicates = [HasStdExtZbp, IsRV32] in {
-def : Pat<(or (and (shl GPR:$rs1, (i32 1)), (i32 0xAAAAAAAA)),
-              (and (srl GPR:$rs1, (i32 1)), (i32 0x55555555))),
-          (GREVI GPR:$rs1, (i32 1))>;
-def : Pat<(or (and (shl GPR:$rs1, (i32 2)), (i32 0xCCCCCCCC)),
-              (and (srl GPR:$rs1, (i32 2)), (i32 0x33333333))),
-          (GREVI GPR:$rs1, (i32 2))>;
-def : Pat<(or (and (shl GPR:$rs1, (i32 4)), (i32 0xF0F0F0F0)),
-              (and (srl GPR:$rs1, (i32 4)), (i32 0x0F0F0F0F))),
-          (GREVI GPR:$rs1, (i32 4))>;
-def : Pat<(or (and (shl GPR:$rs1, (i32 8)), (i32 0xFF00FF00)),
-              (and (srl GPR:$rs1, (i32 8)), (i32 0x00FF00FF))),
-          (GREVI GPR:$rs1, (i32 8))>;
 def : Pat<(rotr (bswap GPR:$rs1), (i32 16)), (GREVI GPR:$rs1, (i32 8))>;
 // FIXME: Is grev better than rori?
 def : Pat<(rotl GPR:$rs1, (i32 16)), (GREVI GPR:$rs1, (i32 16))>;
@@ -775,21 +732,6 @@
 } // Predicates = [HasStdExtZbp, IsRV32]
 
 let Predicates = [HasStdExtZbp, IsRV64] in {
-def : Pat<(or (and (shl GPR:$rs1, (i64 1)), (i64 0xAAAAAAAAAAAAAAAA)),
-              (and (srl GPR:$rs1, (i64 1)), (i64 0x5555555555555555))),
-          (GREVI GPR:$rs1, (i64 1))>;
-def : Pat<(or (and (shl GPR:$rs1, (i64 2)), (i64 0xCCCCCCCCCCCCCCCC)),
-              (and (srl GPR:$rs1, (i64 2)), (i64 0x3333333333333333))),
-          (GREVI GPR:$rs1, (i64 2))>;
-def : Pat<(or (and (shl GPR:$rs1, (i64 4)), (i64 0xF0F0F0F0F0F0F0F0)),
-              (and (srl GPR:$rs1, (i64 4)), (i64 0x0F0F0F0F0F0F0F0F))),
-          (GREVI GPR:$rs1, (i64 4))>;
-def : Pat<(or (and (shl GPR:$rs1, (i64 8)), (i64 0xFF00FF00FF00FF00)),
-              (and (srl GPR:$rs1, (i64 8)), (i64 0x00FF00FF00FF00FF))),
-          (GREVI GPR:$rs1, (i64 8))>;
-def : Pat<(or (and (shl GPR:$rs1, (i64 16)), (i64 0xFFFF0000FFFF0000)),
-              (and (srl GPR:$rs1, (i64 16)), (i64 0x0000FFFF0000FFFF))),
-          (GREVI GPR:$rs1, (i64 16))>;
 // FIXME: Is grev better than rori?
 def : Pat<(rotl GPR:$rs1, (i64 32)), (GREVI GPR:$rs1, (i64 32))>;
 def : Pat<(rotr GPR:$rs1, (i64 32)), (GREVI GPR:$rs1, (i64 32))>;
@@ -962,55 +904,9 @@
           (RORIW GPR:$rs1, uimmlog2xlen:$shamt)>;
 
 let Predicates = [HasStdExtZbp, IsRV64] in {
-def : Pat<(sext_inreg (or (or (and (srl GPR:$rs1, (i64 1)), (i64 0x55555555)),
-                              GPR:$rs1),
-                          (and (shl GPR:$rs1, (i64 1)), (i64 0xAAAAAAAA))),
-                      i32),
-          (GORCIW GPR:$rs1, (i64 1))>;
-def : Pat<(sext_inreg (or (or (and (srl GPR:$rs1, (i64 2)), (i64 0x33333333)),
-                              GPR:$rs1),
-                          (and (shl GPR:$rs1, (i64 2)), (i64 0xCCCCCCCC))),
-                      i32),
-          (GORCIW GPR:$rs1, (i64 2))>;
-def : Pat<(sext_inreg (or (or (and (srl GPR:$rs1, (i64 4)), (i64 0x0F0F0F0F)),
-                              GPR:$rs1),
-                          (and (shl GPR:$rs1, (i64 4)), (i64 0xF0F0F0F0))),
-                      i32),
-          (GORCIW GPR:$rs1, (i64 4))>;
-def : Pat<(sext_inreg (or (or (and (srl GPR:$rs1, (i64 8)), (i64 0x00FF00FF)),
-                              GPR:$rs1),
-                          (and (shl GPR:$rs1, (i64 8)), (i64 0xFF00FF00))),
-                      i32),
-          (GORCIW GPR:$rs1, (i64 8))>;
-def : Pat<(sext_inreg (or (or (and (srl GPR:$rs1, (i64 16)), (i64 0x0000FFFF)),
-                              GPR:$rs1),
-                          (and (shl GPR:$rs1, (i64 16)), (i64 0xFFFF0000))),
-                      i32),
-          (GORCIW GPR:$rs1, (i64 16))>;
-def : Pat<(sext_inreg (or (or (srl (and GPR:$rs1, (i64 0xFFFF0000)), (i64 16)),
-                              GPR:$rs1),
-                          (shl GPR:$rs1, (i64 16))), i32),
-          (GORCIW GPR:$rs1, (i64 16))>;
-
-def : Pat<(sext_inreg (or (and (shl GPR:$rs1, (i64 1)), (i64 0xAAAAAAAA)),
-                          (and (srl GPR:$rs1, (i64 1)), (i64 0x55555555))),
-                      i32),
-          (GREVIW GPR:$rs1, (i64 1))>;
-def : Pat<(sext_inreg (or (and (shl GPR:$rs1, (i64 2)), (i64 0xCCCCCCCC)),
-                          (and (srl GPR:$rs1, (i64 2)), (i64 0x33333333))),
-                      i32),
-          (GREVIW GPR:$rs1, (i64 2))>;
-def : Pat<(sext_inreg (or (and (shl GPR:$rs1, (i64 4)), (i64 0xF0F0F0F0)),
-                          (and (srl GPR:$rs1, (i64 4)), (i64 0x0F0F0F0F))),
-                      i32),
-          (GREVIW GPR:$rs1, (i64 4))>;
-def : Pat<(sext_inreg (or (and (shl GPR:$rs1, (i64 8)), (i64 0xFF00FF00)),
-                          (and (srl GPR:$rs1, (i64 8)), (i64 0x00FF00FF))),
-                      i32),
-          (GREVIW GPR:$rs1, (i64 8))>;
-def : Pat<(sext_inreg (or (shl GPR:$rs1, (i64 16)),
-                          (srl (and GPR:$rs1, 0xFFFF0000), (i64 16))), i32),
-          (GREVIW GPR:$rs1, (i64 16))>;
+def : Pat<(riscv_greviw GPR:$rs1, timm:$shamt), (GREVIW GPR:$rs1, timm:$shamt)>;
+def : Pat<(riscv_gorciw GPR:$rs1, timm:$shamt), (GORCIW GPR:$rs1, timm:$shamt)>;
+
 def : Pat<(sra (bswap GPR:$rs1), (i64 32)), (GREVIW GPR:$rs1, (i64 24))>;
 def : Pat<(sra (bitreverse GPR:$rs1), (i64 32)), (GREVIW GPR:$rs1, (i64 31))>;
 } // Predicates = [HasStdExtZbp, IsRV64]