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

[Craig Topper via llvm-commits]

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@@ -1998,6 +1998,66 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
 
   return true;
 }
+#elif defined(__linux__) && defined(__riscv)
+// struct riscv_hwprobe
+struct RISCVHwProbe {
+  int64_t Key;
+  uint64_t Value;
+};
+bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
+  RISCVHwProbe Query[]{{/*RISCV_HWPROBE_KEY_IMA_EXT_0=*/4, 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)
+    return false;
+
+  uint64_t ExtMask = Query[0].Value;
+  Features["f"] = ExtMask & (1 << 0);           // RISCV_HWPROBE_IMA_FD
+  Features["d"] = ExtMask & (1 << 0);           // RISCV_HWPROBE_IMA_FD
+  Features["c"] = ExtMask & (1 << 1);           // RISCV_HWPROBE_IMA_C
+  Features["v"] = ExtMask & (1 << 2);           // RISCV_HWPROBE_IMA_V
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topperc wrote:

What about "a" and "m"? Do we need to check RISCV_HWPROBE_KEY_BASE_BEHAVIOR?

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