[llvm] Add Apple M4 host detection (PR #117530)

[Ruoyu Zhong via llvm-commits]

================
@@ -1496,13 +1508,46 @@ StringRef sys::getHostCPUName() {
 #define CPUFAMILY_ARM_FIRESTORM_ICESTORM 0x1b588bb3
 #define CPUFAMILY_ARM_BLIZZARD_AVALANCHE 0xda33d83d
 #define CPUFAMILY_ARM_EVEREST_SAWTOOTH 0x8765edea
+#define CPUFAMILY_ARM_IBIZA 0xfa33415e
+#define CPUFAMILY_ARM_PALMA 0x72015832
+#define CPUFAMILY_ARM_COLL 0x2876f5b5
+#define CPUFAMILY_ARM_LOBOS 0x5f4dea93
+#define CPUFAMILY_ARM_DONAN 0x6f5129ac
+#define CPUFAMILY_ARM_BRAVA 0x17d5b93a
+#define CPUFAMILY_ARM_TAHITI 0x75d4acb9
+#define CPUFAMILY_ARM_TUPAI 0x204526d0
 
 StringRef sys::getHostCPUName() {
   uint32_t Family;
   size_t Length = sizeof(Family);
   sysctlbyname("hw.cpufamily", &Family, &Length, NULL, 0);
 
+  // This is found by testing on actual hardware, and by looking at:
+  // https://github.com/apple-oss-distributions/xnu/blob/xnu-11215.41.3/osfmk/arm/cpuid.c#L109-L231.
+  //
+  // Another great resource is
+  // https://github.com/AsahiLinux/docs/wiki/Codenames.
+  //
+  // NOTE: We choose to return `apple-mX` instead of `apple-aX`, since the M1,
+  // M2, M3 etc. aliases are more widely known to users than A14, A15, A16 etc.
+  // (and this code is basically only used on host macOS anyways).
   switch (Family) {
+  case CPUFAMILY_UNKNOWN:
+    return "generic";
+  case CPUFAMILY_ARM_9:
+    return "arm920t"; // or arm926ej-s
+  case CPUFAMILY_ARM_11:
+    return "arm1136jf-s";
+  case CPUFAMILY_ARM_XSCALE:
+    return "xscale";
+  case CPUFAMILY_ARM_12:
+    return "generic"; // Seems unsued by the kernel
----------------
ZhongRuoyu wrote:

```suggestion
    return "generic"; // Seems unused by the kernel
```

(Thanks for your work, by the way!)


https://github.com/llvm/llvm-project/pull/117530