[llvm] [RISCV] Get host CPU name via hwprobe (PR #142745)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp updated https://github.com/llvm/llvm-project/pull/142745

>From 4914cddaae16bb1a64c417acb0bb3abb3b697909 Mon Sep 17 00:00:00 2001
From: Pengcheng Wang <wangpengcheng.pp at bytedance.com>
Date: Wed, 4 Jun 2025 16:58:39 +0800
Subject: [PATCH 1/3] [RISCV] Get host CPU name via hwprobe

We can get the `mvendorid/marchid/mimpid` via hwprobe and then we
can compare these IDs with those defined in processors to find the
CPU name.

With this change, `-mcpu/-mtune=native` can set the proper name.
---
 .../llvm/TargetParser/RISCVTargetParser.h     |  8 ++++++
 llvm/lib/TargetParser/Host.cpp                | 26 +++++++++++++++----
 llvm/lib/TargetParser/RISCVTargetParser.cpp   | 15 ++++++++---
 3 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/llvm/include/llvm/TargetParser/RISCVTargetParser.h b/llvm/include/llvm/TargetParser/RISCVTargetParser.h
index a529479b546d9..f94e05ee7d30b 100644
--- a/llvm/include/llvm/TargetParser/RISCVTargetParser.h
+++ b/llvm/include/llvm/TargetParser/RISCVTargetParser.h
@@ -28,6 +28,13 @@ struct CPUModel {
   uint32_t MVendorID;
   uint64_t MArchID;
   uint64_t MImpID;
+
+  bool isValid() const { return MVendorID != 0 && MArchID != 0 && MImpID != 0; }
+
+  bool operator==(const CPUModel &Other) const {
+    return MVendorID == Other.MVendorID && MArchID == Other.MArchID &&
+           MImpID == Other.MImpID;
+  }
 };
 
 struct CPUInfo {
@@ -55,6 +62,7 @@ bool hasFastScalarUnalignedAccess(StringRef CPU);
 bool hasFastVectorUnalignedAccess(StringRef CPU);
 bool hasValidCPUModel(StringRef CPU);
 CPUModel getCPUModel(StringRef CPU);
+StringRef getCPUNameFromCPUModel(const CPUModel &Model);
 
 } // namespace RISCV
 
diff --git a/llvm/lib/TargetParser/Host.cpp b/llvm/lib/TargetParser/Host.cpp
index 14acef116708a..13f029e792c01 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1672,8 +1672,29 @@ StringRef sys::getHostCPUName() {
   return "generic";
 }
 #elif defined(__riscv)
+// struct riscv_hwprobe
+struct RISCVHwProbe {
+  int64_t Key;
+  uint64_t Value;
+};
+
 StringRef sys::getHostCPUName() {
 #if defined(__linux__)
+  // Try hwprobe way first.
+  RISCVHwProbe Query[]{{/*RISCV_HWPROBE_KEY_MVENDORID=*/0, 0},
+                       {/*RISCV_HWPROBE_KEY_MARCHID=*/1, 0},
+                       {/*RISCV_HWPROBE_KEY_MIMPID=*/2, 0}};
+  int Ret = syscall(/*__NR_riscv_hwprobe=*/258, /*pairs=*/Query,
+                    /*pair_count=*/std::size(Query), /*cpu_count=*/0,
+                    /*cpus=*/0, /*flags=*/0);
+  if (Ret == 0) {
+    RISCV::CPUModel Model{pairs[0].value, pairs[1].value, pairs[2].value};
+    StringRef Name = RISCV::getCPUNameFromCPUModel(Model);
+    if (!Name.empty())
+      return Name;
+  }
+
+  // Then try the cpuinfo way.
   std::unique_ptr<llvm::MemoryBuffer> P = getProcCpuinfoContent();
   StringRef Content = P ? P->getBuffer() : "";
   StringRef Name = detail::getHostCPUNameForRISCV(Content);
@@ -2148,11 +2169,6 @@ const StringMap<bool> sys::getHostCPUFeatures() {
   return Features;
 }
 #elif defined(__linux__) && defined(__riscv)
-// struct riscv_hwprobe
-struct RISCVHwProbe {
-  int64_t Key;
-  uint64_t Value;
-};
 const StringMap<bool> sys::getHostCPUFeatures() {
   RISCVHwProbe Query[]{{/*RISCV_HWPROBE_KEY_BASE_BEHAVIOR=*/3, 0},
                        {/*RISCV_HWPROBE_KEY_IMA_EXT_0=*/4, 0},
diff --git a/llvm/lib/TargetParser/RISCVTargetParser.cpp b/llvm/lib/TargetParser/RISCVTargetParser.cpp
index 2e5e8f4e50c9c..9957ec0c28d88 100644
--- a/llvm/lib/TargetParser/RISCVTargetParser.cpp
+++ b/llvm/lib/TargetParser/RISCVTargetParser.cpp
@@ -57,10 +57,7 @@ bool hasFastVectorUnalignedAccess(StringRef CPU) {
   return Info && Info->FastVectorUnalignedAccess;
 }
 
-bool hasValidCPUModel(StringRef CPU) {
-  const CPUModel Model = getCPUModel(CPU);
-  return Model.MVendorID != 0 && Model.MArchID != 0 && Model.MImpID != 0;
-}
+bool hasValidCPUModel(StringRef CPU) { return getCPUModel(CPU).isValid(); }
 
 CPUModel getCPUModel(StringRef CPU) {
   const CPUInfo *Info = getCPUInfoByName(CPU);
@@ -69,6 +66,16 @@ CPUModel getCPUModel(StringRef CPU) {
   return Info->Model;
 }
 
+StringRef getCPUNameFromCPUModel(const CPUModel &Model) {
+  if (!Model.isValid())
+    return "";
+
+  for (auto &C : RISCVCPUInfo)
+    if (C.Model == Model)
+      return C.Name;
+  return "";
+}
+
 bool parseCPU(StringRef CPU, bool IsRV64) {
   const CPUInfo *Info = getCPUInfoByName(CPU);
 

>From 632db80936014fdf078691b7db63af8c1f9852a8 Mon Sep 17 00:00:00 2001
From: Pengcheng Wang <wangpengcheng.pp at bytedance.com>
Date: Thu, 5 Jun 2025 11:55:36 +0800
Subject: [PATCH 2/3] Guard struct RISCVHwProbe by __linux__ macro

---
 llvm/lib/TargetParser/Host.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/llvm/lib/TargetParser/Host.cpp b/llvm/lib/TargetParser/Host.cpp
index 13f029e792c01..8cb33add5f06f 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1672,11 +1672,13 @@ StringRef sys::getHostCPUName() {
   return "generic";
 }
 #elif defined(__riscv)
+#if defined(__linux__)
 // struct riscv_hwprobe
 struct RISCVHwProbe {
   int64_t Key;
   uint64_t Value;
 };
+#endif
 
 StringRef sys::getHostCPUName() {
 #if defined(__linux__)

>From 09d135e6abdc318b1a6b47da883ef33f0339bd35 Mon Sep 17 00:00:00 2001
From: Pengcheng Wang <wangpengcheng.pp at bytedance.com>
Date: Thu, 5 Jun 2025 11:57:29 +0800
Subject: [PATCH 3/3] fix comment

---
 llvm/lib/TargetParser/Host.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/TargetParser/Host.cpp b/llvm/lib/TargetParser/Host.cpp
index 8cb33add5f06f..b0d21591aeb05 100644
--- a/llvm/lib/TargetParser/Host.cpp
+++ b/llvm/lib/TargetParser/Host.cpp
@@ -1682,7 +1682,7 @@ struct RISCVHwProbe {
 
 StringRef sys::getHostCPUName() {
 #if defined(__linux__)
-  // Try hwprobe way first.
+  // Try the hwprobe way first.
   RISCVHwProbe Query[]{{/*RISCV_HWPROBE_KEY_MVENDORID=*/0, 0},
                        {/*RISCV_HWPROBE_KEY_MARCHID=*/1, 0},
                        {/*RISCV_HWPROBE_KEY_MIMPID=*/2, 0}};