[llvm] [Exegesis][RISCV] Add initial RVV support (PR #128767)

[Craig Topper via llvm-commits]

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@@ -0,0 +1,131 @@
+//===- RISCVExegesisPostprocessing.cpp - Post processing MI for exegesis---===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// \file
+// This Pass converts some of the virtual register operands in VSETVLI and FRM
+// pseudos into physical registers.
+//
+//===----------------------------------------------------------------------===//
+
+#include "RISCV.h"
+#include "RISCVExegesisPasses.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "riscv-exegesis-post-processing"
+
+namespace {
+struct RISCVExegesisPostprocessing : public MachineFunctionPass {
+  static char ID;
+
+  RISCVExegesisPostprocessing() : MachineFunctionPass(ID) {}
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+private:
+  // Extremely simple register allocator that picks a register that hasn't
+  // been defined or used in this function.
+  Register allocateGPRRegister(const MachineFunction &MF,
+                               const MachineRegisterInfo &MRI);
+
+  bool processVSETVL(MachineInstr &MI, MachineRegisterInfo &MRI);
+  bool processWriteFRM(MachineInstr &MI, MachineRegisterInfo &MRI);
+};
+} // anonymous namespace
+
+char RISCVExegesisPostprocessing::ID = 0;
+
+bool RISCVExegesisPostprocessing::runOnMachineFunction(MachineFunction &MF) {
+  bool Changed = false;
+  for (auto &MBB : MF)
+    for (auto &MI : MBB) {
+      unsigned Opcode = MI.getOpcode();
+      switch (Opcode) {
+      case RISCV::VSETVLI:
+      case RISCV::VSETVL:
+      case RISCV::PseudoVSETVLI:
+      case RISCV::PseudoVSETVLIX0:
+        Changed |= processVSETVL(MI, MF.getRegInfo());
+        break;
+      case RISCV::SwapFRMImm:
+      case RISCV::WriteFRM:
+        Changed |= processWriteFRM(MI, MF.getRegInfo());
+        break;
+      default:
+        break;
+      }
+    }
+
+  if (Changed)
+    MF.getRegInfo().clearVirtRegs();
+
+  LLVM_DEBUG(MF.print(dbgs() << "===After RISCVExegesisPostprocessing===\n");
+             dbgs() << "\n");
+
+  return Changed;
+}
+
+Register RISCVExegesisPostprocessing::allocateGPRRegister(
+    const MachineFunction &MF, const MachineRegisterInfo &MRI) {
+  const auto &TRI = *MRI.getTargetRegisterInfo();
+
+  // We hope to avoid allocating callee-saved registers. And GPRTC
+  // happens to account for nearly all caller-saved registers.
+  const TargetRegisterClass *GPRClass = TRI.getRegClass(RISCV::GPRTCRegClassID);
+  BitVector Candidates = TRI.getAllocatableSet(MF, GPRClass);
+
+  for (unsigned SetIdx : Candidates.set_bits()) {
+    if (MRI.reg_empty(Register(SetIdx)))
+      return Register(SetIdx);
+  }
+
+  // All bets are off, assign a fixed one.
+  return RISCV::X5;
+}
+
+bool RISCVExegesisPostprocessing::processVSETVL(MachineInstr &MI,
+                                                MachineRegisterInfo &MRI) {
+  bool Changed = false;
+  // Replace both AVL and VL (i.e. the result) operands with physical
+  // registers.
+  for (unsigned Idx = 0U; Idx < 2; ++Idx)
+    if (MI.getOperand(Idx).isReg()) {
+      Register RegOp = MI.getOperand(Idx).getReg();
+      if (RegOp.isVirtual()) {
+        MRI.replaceRegWith(RegOp, allocateGPRRegister(*MI.getMF(), MRI));
+        Changed = true;
+      }
+    }
+
+  return Changed;
+}
+
+bool RISCVExegesisPostprocessing::processWriteFRM(MachineInstr &MI,
+                                                  MachineRegisterInfo &MRI) {
+  // The virtual register will be the first operand in both SwapFRMImm and
+  // WriteFRM.
+  if (MI.getOperand(0).isReg()) {
----------------
topperc wrote:

What can the destination be if its not a register?

https://github.com/llvm/llvm-project/pull/128767