[RISCV][llvm-exegesis] Add default Pfm cycle counter. (llvm#121866)

Also tested with Ubuntu on SiFive's HiFive Premier P550 board. Curiously
latency is reporting ~1.5 on basic scalar arithmetic, scalar mul is
~3.5, and div is ~36.5. This 0.5 cycles higher than I expect.

Author: topperc

llvm/lib/Target/RISCV/CMakeLists.txt

@@ -15,6 +15,7 @@ tablegen(LLVM RISCVGenRegisterBank.inc -gen-register-bank)
 tablegen(LLVM RISCVGenRegisterInfo.inc -gen-register-info)
 tablegen(LLVM RISCVGenSearchableTables.inc -gen-searchable-tables)
 tablegen(LLVM RISCVGenSubtargetInfo.inc -gen-subtarget)
+tablegen(LLVM RISCVGenExegesis.inc -gen-exegesis)
 
 set(LLVM_TARGET_DEFINITIONS RISCVGISel.td)
 tablegen(LLVM RISCVGenGlobalISel.inc -gen-global-isel)

llvm/lib/Target/RISCV/RISCV.td

@@ -63,6 +63,12 @@ include "RISCVSchedXiangShanNanHu.td"
 
 include "RISCVProcessors.td"
 
+//===----------------------------------------------------------------------===//
+// Pfm Counters
+//===----------------------------------------------------------------------===//
+
+include "RISCVPfmCounters.td"
+
 //===----------------------------------------------------------------------===//
 // Define the RISC-V target.
 //===----------------------------------------------------------------------===//

llvm/lib/Target/RISCV/RISCVPfmCounters.td

@@ -0,0 +1,18 @@
+//===---- RISCVPfmCounters.td - RISC-V Hardware Counters ---*- tablegen -*-===//
+//
+// 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 describes the available hardware counters for RISC-V.
+//
+//===----------------------------------------------------------------------===//
+
+def CpuCyclesPfmCounter : PfmCounter<"CYCLES">;
+
+def DefaultPfmCounters : ProcPfmCounters {
+  let CycleCounter = CpuCyclesPfmCounter;
+}
+def : PfmCountersDefaultBinding<DefaultPfmCounters>;

llvm/tools/llvm-exegesis/lib/RISCV/Target.cpp

@@ -24,6 +24,8 @@
 namespace llvm {
 namespace exegesis {
 
+#include "RISCVGenExegesis.inc"
+
 namespace {
 
 // Stores constant value to a general-purpose (integer) register.
@@ -132,8 +134,7 @@ class ExegesisRISCVTarget : public ExegesisTarget {
 };
 
 ExegesisRISCVTarget::ExegesisRISCVTarget()
-    : ExegesisTarget(ArrayRef<CpuAndPfmCounters>{},
-                     RISCV_MC::isOpcodeAvailable) {}
+    : ExegesisTarget(RISCVCpuPfmCounters, RISCV_MC::isOpcodeAvailable) {}
 
 bool ExegesisRISCVTarget::matchesArch(Triple::ArchType Arch) const {
   return Arch == Triple::riscv32 || Arch == Triple::riscv64;

llvm/unittests/tools/llvm-exegesis/RISCV/TargetTest.cpp

@@ -42,6 +42,15 @@ TEST_F(RISCVTargetTest, SetRegToConstant) {
   EXPECT_THAT(Insts, Not(IsEmpty()));
 }
 
+TEST_F(RISCVTargetTest, DefaultPfmCounters) {
+  const std::string Expected = "CYCLES";
+  EXPECT_EQ(State.getExegesisTarget().getPfmCounters("").CycleCounter,
+            Expected);
+  EXPECT_EQ(
+      State.getExegesisTarget().getPfmCounters("unknown_cpu").CycleCounter,
+      Expected);
+}
+
 } // namespace
 } // namespace exegesis
 } // namespace llvm