[llvm] [RISCV][MachineCombiner] Add reassociation optimizations for RVV instructions (PR #88307)

[Craig Topper via llvm-commits]

================
@@ -1619,8 +1619,184 @@ static bool isFMUL(unsigned Opc) {
   }
 }
 
+bool RISCVInstrInfo::isVectorAssociativeAndCommutative(const MachineInstr &Inst,
+                                                       bool Invert) const {
+#define OPCODE_LMUL_CASE(OPC)                                                  \
+  case RISCV::OPC##_M1:                                                        \
+  case RISCV::OPC##_M2:                                                        \
+  case RISCV::OPC##_M4:                                                        \
+  case RISCV::OPC##_M8:                                                        \
+  case RISCV::OPC##_MF2:                                                       \
+  case RISCV::OPC##_MF4:                                                       \
+  case RISCV::OPC##_MF8
+
+#define OPCODE_LMUL_MASK_CASE(OPC)                                             \
+  case RISCV::OPC##_M1_MASK:                                                   \
+  case RISCV::OPC##_M2_MASK:                                                   \
+  case RISCV::OPC##_M4_MASK:                                                   \
+  case RISCV::OPC##_M8_MASK:                                                   \
+  case RISCV::OPC##_MF2_MASK:                                                  \
+  case RISCV::OPC##_MF4_MASK:                                                  \
+  case RISCV::OPC##_MF8_MASK
+
+  unsigned Opcode = Inst.getOpcode();
+  if (Invert) {
+    if (auto InvOpcode = getInverseOpcode(Opcode))
+      Opcode = *InvOpcode;
+    else
+      return false;
+  }
+
+  // clang-format off
+  switch (Opcode) {
+  default:
+    return false;
+  OPCODE_LMUL_CASE(PseudoVADD_VV):
+  OPCODE_LMUL_MASK_CASE(PseudoVADD_VV):
+  OPCODE_LMUL_CASE(PseudoVMUL_VV):
+  OPCODE_LMUL_MASK_CASE(PseudoVMUL_VV):
+  OPCODE_LMUL_CASE(PseudoVMULH_VV):
+  OPCODE_LMUL_MASK_CASE(PseudoVMULH_VV):
+  OPCODE_LMUL_CASE(PseudoVMULHU_VV):
+  OPCODE_LMUL_MASK_CASE(PseudoVMULHU_VV):
+    return true;
+  }
+  // clang-format on
+
+#undef OPCODE_LMUL_MASK_CASE
+#undef OPCODE_LMUL_CASE
+}
+
+bool RISCVInstrInfo::areRVVInstsReassociable(const MachineInstr &MI1,
+                                             const MachineInstr &MI2) const {
+  if (!areOpcodesEqualOrInverse(MI1.getOpcode(), MI2.getOpcode()))
+    return false;
+
+  // Make sure vtype operands are also the same.
+  const MCInstrDesc &Desc = get(MI1.getOpcode());
+  const uint64_t TSFlags = Desc.TSFlags;
+
+  auto checkImmOperand = [&](unsigned OpIdx) {
+    return MI1.getOperand(OpIdx).getImm() == MI2.getOperand(OpIdx).getImm();
+  };
+
+  auto checkRegOperand = [&](unsigned OpIdx) {
+    return MI1.getOperand(OpIdx).getReg() == MI2.getOperand(OpIdx).getReg();
+  };
+
+  // PassThru
+  if (!checkRegOperand(1))
+    return false;
+
+  // SEW
+  if (RISCVII::hasSEWOp(TSFlags) &&
+      !checkImmOperand(RISCVII::getSEWOpNum(Desc)))
+    return false;
+
+  // Mask
+  // There might be more sophisticated ways to check equality of masks, but
+  // right now we simply check if they're the same virtual register.
+  if (RISCVII::usesMaskPolicy(TSFlags) && !checkRegOperand(4))
+    return false;
+
+  // Tail / Mask policies
+  if (RISCVII::hasVecPolicyOp(TSFlags) &&
+      !checkImmOperand(RISCVII::getVecPolicyOpNum(Desc)))
+    return false;
+
+  // VL
+  if (RISCVII::hasVLOp(TSFlags)) {
+    unsigned OpIdx = RISCVII::getVLOpNum(Desc);
+    const MachineOperand &Op1 = MI1.getOperand(OpIdx);
+    const MachineOperand &Op2 = MI2.getOperand(OpIdx);
+    if (Op1.getType() != Op2.getType())
+      return false;
+    switch (Op1.getType()) {
+    case MachineOperand::MO_Register:
+      if (Op1.getReg() != Op2.getReg())
+        return false;
+      break;
+    case MachineOperand::MO_Immediate:
+      if (Op1.getImm() != Op2.getImm())
+        return false;
+      break;
+    default:
+      llvm_unreachable("Unrecognized VL operand type");
+    }
+  }
+
+  // Rounding modes
+  if (RISCVII::hasRoundModeOp(TSFlags) &&
+      !checkImmOperand(RISCVII::getVLOpNum(Desc) - 1))
+    return false;
+
+  return true;
+}
+
+// Most of our RVV pseudo has passthru operand, so the real operands
----------------
topperc wrote:

"pseudos have"

https://github.com/llvm/llvm-project/pull/88307