[llvm] [Exegesis][RISCV] Add RISCV support for llvm-exegesis (PR #89047)

[via llvm-commits]

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@@ -0,0 +1,100 @@
+//===-- RISCVCounters.cpp ---------------------------------------*- C++ -*-===//
+//
+// 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 defines RISC-V perf counters.
+//
+//===----------------------------------------------------------------------===//
+
+#include "RISCVCounters.h"
+
+namespace llvm {
+namespace exegesis {
+
+// This implementation of RISCV target for Exegesis doesn't use libpfm
+// and provides manual implementation of performance counters.
+
+inline uint64_t getRISCVCpuCyclesCount() {
+#if defined(__riscv) && defined(__linux__)
+#if __riscv_xlen == 32
+  uint32_t cycles_lo, cycles_hi0, cycles_hi1;
+  asm volatile("rdcycleh %0\n"
+               "rdcycle %1\n"
+               "rdcycleh %2\n"
+               "sub %0, %0, %2\n"
+               "seqz %0, %0\n"
+               "sub %0, zero, %0\n"
+               "and %1, %1, %0\n"
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AnastasiyaChernikova wrote:

Changed the algorithm for a 32-bit system. I propose to leave it this way for now and fix in future contributions, since this section of code cannot be run at all yet, since we do not support jit mode

https://github.com/llvm/llvm-project/pull/89047