[compiler-rt] [XRay][SystemZ] Use stckf for non-clang compilers (PR #125289)

[Fangrui Song via llvm-commits]

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@@ -96,7 +96,13 @@ namespace __xray {
 inline bool probeRequiredCPUFeatures() XRAY_NEVER_INSTRUMENT { return true; }
 
 ALWAYS_INLINE uint64_t readTSC(uint8_t &CPU) XRAY_NEVER_INSTRUMENT {
+#if defined(__clang__)
   return __builtin_readcyclecounter();
+#else
+  uint64_t Cycles;
+  asm volatile("stckf %0" : /* No output. */ : "Q"(Cycles) : "cc");
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MaskRay wrote:

remove the unnecessary comment `/* No output. */`. In the majority of places we assume that the user is aware of the `: : ` syntax

https://github.com/llvm/llvm-project/pull/125289