[llvm] [RISCV64] liveness analysis (PR #167454)

[Alex Bradbury via llvm-commits]

================
@@ -0,0 +1,598 @@
+//===- RISCVLiveVariables.cpp - Live Variable Analysis for RISC-V --------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a live variable analysis pass for the RISC-V backend.
+// The pass computes liveness information for virtual and physical registers
+// in RISC-V machine functions, optimized for RV64 (64-bit RISC-V architecture).
+//
+// The analysis performs a backward dataflow analysis to compute
+// liveness information. Also updates the kill flags on register operands.
+// There is also a verification step to ensure consistency with MBB live-ins.
+//
+//===----------------------------------------------------------------------===//
+
+#include "RISCV.h"
+#include "RISCVInstrInfo.h"
+#include "RISCVSubtarget.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/TargetRegisterInfo.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include <set>
+#include <unordered_map>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "riscv-live-variables"
+#define RISCV_LIVE_VARIABLES_NAME "RISC-V Live Variable Analysis"
+
+STATISTIC(NumLiveRegsAtEntry, "Number of registers live at function entry");
+STATISTIC(NumLiveRegsTotal, "Total number of live registers across all blocks");
+
+static cl::opt<bool> UpdateKills("riscv-liveness-update-kills",
+                                 cl::desc("Update kill flags"), cl::init(false),
+                                 cl::Hidden);
+
+static cl::opt<bool> UpdateLiveIns("riscv-liveness-update-mbb-liveins",
+                                   cl::desc("Update MBB live-in sets"),
+                                   cl::init(false), cl::Hidden);
+
+static cl::opt<unsigned> MaxVRegs("riscv-liveness-max-vregs",
+                                  cl::desc("Maximum VRegs to track"),
+                                  cl::init(1024), cl::Hidden);
+
+static cl::opt<unsigned> VerifyLiveness("riscv-liveness-verify",
----------------
asb wrote:

Should be `cl::opt<bool>`?

https://github.com/llvm/llvm-project/pull/167454