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

[Yingwei Zheng via cfe-commits]

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@@ -2002,6 +2003,76 @@ 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_BASE_BEHAVIOR=*/3, 0},
+                       {/*RISCV_HWPROBE_KEY_IMA_EXT_0=*/4, 0}};
+  int Ret = syscall(/*__NR_riscv_hwprobe=*/258, /*pairs=*/Query,
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dtcxzyw wrote:

Currently `sys::getHostCPUFeatures` has three callers:
+ clang -> `riscv::getRISCVTargetFeatures`
+ llvm-tools -> `codegen::getFeaturesStr`
+ JIT users -> `JITTargetMachineBuilder::detectHost`

I don't think there are any opportunities to reuse the result.
BTW, https://github.com/llvm/llvm-project/pull/85790 may benefit from the vDSO symbol, but it implements caching itself.

I didn't use the glibc call `__riscv_hwprobe` since `sys/hwprobe.h` was unavailable on my RV board :(


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