[llvm] [RISCV] Add support for getHostCPUFeatures using hwprobe (PR #94352)

[Yingwei Zheng via llvm-commits]

================
@@ -1998,6 +1998,74 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
 
   return true;
 }
+#elif defined(__linux__) && defined(__riscv)
+#ifdef __has_include
+#if __has_include(<asm/hwprobe.h>)
+#include <asm/hwprobe.h>
+#endif
+#endif
+bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
+#ifdef RISCV_HWPROBE_KEY_MVENDORID
+  riscv_hwprobe Query[2]{
+      {RISCV_HWPROBE_KEY_IMA_EXT_0, 0},
+      {RISCV_HWPROBE_KEY_CPUPERF_0, 0},
+  };
+  int Ret = syscall(/*__NR_riscv_hwprobe=*/258, /*pairs=*/&Query,
+                    /*pair_count=*/1, /*cpu_count=*/0, /*cpus=*/0, /*flags=*/0);
+  if (Ret != 0)
+    return false;
+
+  uint64_t ExtMask = Query[0].value;
+  Features["f"] = ExtMask & RISCV_HWPROBE_IMA_FD;
+  Features["d"] = ExtMask & RISCV_HWPROBE_IMA_FD;
+  Features["c"] = ExtMask & RISCV_HWPROBE_IMA_C;
+  Features["v"] = ExtMask & RISCV_HWPROBE_IMA_V;
+  Features["zba"] = ExtMask & RISCV_HWPROBE_IMA_ZBA;
----------------
dtcxzyw wrote:

```suggestion
  Features["zba"] = ExtMask & RISCV_HWPROBE_EXT_ZBA;
```

https://github.com/llvm/llvm-project/pull/94352