[llvm] [BOLT][AArch64] Introduce SPE mode in BasicAggregation (PR #120741)

[Paschalis Mpeis via llvm-commits]

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@@ -180,22 +187,29 @@ void DataAggregator::start() {
 
   findPerfExecutable();
 
-  if (opts::BasicAggregation) {
-    launchPerfProcess("events without LBR",
-                      MainEventsPPI,
+  if (opts::ArmSPE) {
+    if (!opts::BasicAggregation) {
+      errs() << "PERF2BOLT-ERROR: Arm SPE mode is combined only with "
+                "BasicAggregation.\n";
+      exit(1);
+    }
+    launchPerfProcess("branch events with SPE", MainEventsPPI,
+                      "script -F pid,event,ip,addr --itrace=i1i",
----------------
paschalis-mpeis wrote:


Hey Maks,

We expect:
- branch entries to have non-zero values for both `addr` and `ip`
- non-branch entries to have non-zero value only for `ip`

This [unit test](https://github.com/llvm/llvm-project/pull/120741/files#diff-b16a95c2248de4f899b4bea1591c813c69caed2f5e3702ea53e0a80d75b1a79cR133) illustrates such an output.


> On my system ip is always 0 for the data collected  ...

The zeros you are seeing actually refer to `addr` and not `ip`. It is a bit confusing but the printed order is different than the fields order specified in CLI. Can verify using:
```bash
perf script -F pid,event,ip ..
perf script -F pid,event,addr .. # seeing zeros on unpatched perf
```

> The zeros on my side could be b/c we don't have kernel patches listed in [#115333](https://github.com/llvm/llvm-project/issues/115333).

Correct. We believe these patches might make it to the next kernel RC.  
In the meantime, I've added some [sample instructions](https://github.com/llvm/llvm-project/issues/115333#issuecomment-2597809642) on the issue to quickly use it locally, w/o requiring to re-flush a kernel.


https://github.com/llvm/llvm-project/pull/120741