[llvm] [RISCV] Use vlenb CSR to set Zvl*b feature getHostCPUFeatures. (PR #225486)

[Craig Topper via llvm-commits]

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@@ -2618,6 +2618,24 @@ StringMap<bool> sys::getHostCPUFeatures() {
       Query[2].Value == /*RISCV_HWPROBE_MISALIGNED_SCALAR_FAST=*/3)
     Features["unaligned-scalar-mem"] = true;
 
+  // Infer Zvl from vlenb CSR.
+  if (Features["v"] || Features["zve32x"]) {
+#if __riscv_xlen == 64
+    uint64_t VLen;
+#elif __riscv_xlen == 32
+    uint32_t VLen;
+#else
+#error "Unknown XLEN"
+#endif
+    // Use the raw CSR number in case assembler doesn't know vlenb.
+    __asm__ volatile("csrr %0, 0xc22" : "=r"(VLen));
+    if (VLen) {
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topperc wrote:

I guess it wouldn't. I'll remove

https://github.com/llvm/llvm-project/pull/225486