[llvm] [llvm-exegesis][AArch64] Disable pauth and ldgm as unsupported instructions (PR #132346)

[David Green via llvm-commits]

================
@@ -9,12 +9,54 @@
 #include "AArch64.h"
 #include "AArch64RegisterInfo.h"
 
+#include <linux/prctl.h> // For PR_PAC_* constants
+#include <sys/prctl.h>
+
 #define GET_AVAILABLE_OPCODE_CHECKER
 #include "AArch64GenInstrInfo.inc"
 
 namespace llvm {
 namespace exegesis {
 
+bool isPointerAuth(unsigned Opcode) {
+  switch (Opcode) {
+  default:
+    return false;
+
+  // FIXME: Pointer Authentication instructions.
+  // We would like to measure these instructions, but they can behave
+  // differently on different platforms, and maybe the snippets need to look
+  // different for these instructions, so we disable PAC keys via prctl to allow
+  // measuring them without authentication failures.
----------------
davemgreen wrote:

This comment can be updated now? It might be worth adding note, possibly below where prctl is called, that we expect / hope that the costs measured are the same with the pac keys disabled, but they could be lower.

https://github.com/llvm/llvm-project/pull/132346