[llvm] Add initial support for SPE brstack format (PR #129231)

[Amir Ayupov via llvm-commits]

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@@ -181,11 +184,19 @@ void DataAggregator::start() {
 
   findPerfExecutable();
 
-  if (opts::BasicAggregation) {
-    launchPerfProcess("events without LBR",
-                      MainEventsPPI,
+  if (opts::ArmSPE) {
+    // pid    from_ip      to_ip        flags
+    // where flags could be:
+    // P/M: whether branch was Predicted or Mispredicted.
+    // N: optionally appears when the branch was Not-Taken (ie fall-through)
+    // 12345  0x123/0x456/PN/-/-/8/RET/-
+    launchPerfProcess("SPE brstack events", MainEventsPPI,
+                      "script -F pid,brstack --itrace=bl",
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aaupov wrote:

Can we just override `itrace` if ArmSPE is set?

https://github.com/llvm/llvm-project/pull/129231