[llvm] [BOLT] Adding a unittest that covers Arm SPE PBT aggregation (PR #160095)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-bolt

Author: Ádám Kallai (kaadam)

<details>
<summary>Changes</summary>

When the SPE previous branch target address (named as PBT) feature is available, it records the previous branch target before the sampled operation.

One SPE sample by combining this feature, has two entries. It forms a chain of two consecutive branches. Arm SPE stores the latest branch into the first entry, and the previous branch address is stored into the second entry. However PBT doesn't provide as much information as SPE does. It lacks those information such as the address of source branch, branch type, and prediction bit. These information filled with zero.

Consider the following example:

FROM/TO/P/-/-/1/COND/-  FROM/TO/-/-/-/0//-
0xffff8000807216b4/0xffff800080721704/P/-/-/1/COND/-  0x0/0xffff8000807216ac/-/-/-/0//-

Where the first entry is the newest pair, the second one is the oldest pair.

---
Full diff: https://github.com/llvm/llvm-project/pull/160095.diff


1 Files Affected:

- (modified) bolt/unittests/Profile/PerfSpeEvents.cpp (+47) 


``````````diff
diff --git a/bolt/unittests/Profile/PerfSpeEvents.cpp b/bolt/unittests/Profile/PerfSpeEvents.cpp
index 8d023cd7b7e74..0ec4651a5ae17 100644
--- a/bolt/unittests/Profile/PerfSpeEvents.cpp
+++ b/bolt/unittests/Profile/PerfSpeEvents.cpp
@@ -161,4 +161,51 @@ TEST_F(PerfSpeEventsTestHelper, SpeBranchesWithBrstack) {
   parseAndCheckBrstackEvents(1234, ExpectedSamples);
 }
 
+TEST_F(PerfSpeEventsTestHelper, SpeBranchesWithBrstackAndPbt) {
+  // Check perf input with SPE branch events as brstack format by
+  // combining with the previous branch target address (named as PBT).
+  // Example collection command:
+  // ```
+  // perf record -e 'arm_spe_0/branch_filter=1/u' -- BINARY
+  // ```
+  // How Bolt extracts the branch events:
+  // ```
+  // perf script -F pid,brstack --itrace=bl
+  // ```
+
+  opts::ArmSPE = true;
+  opts::ReadPerfEvents = "  4567  0xa002/0xa003/PN/-/-/10/COND/- 0x0/0xa001/-/-/-/0//-\n"
+                         "  4567  0xb002/0xb003/P/-/-/4/RET/- 0x0/0xb001/-/-/-/0//-\n"
+                         "  4567  0xc456/0xc789/P/-/-/13/-/- 0x0/0xc123/-/-/-/0//-\n"
+                         "  4567  0xd456/0xd789/M/-/-/7/RET/- 0x0/0xd123/-/-/-/0//-\n"
+                         "  4567  0xe005/0xe009/P/-/-/14/RET/- 0x0/0xe001/-/-/-/0//-\n"
+                         "  4567  0xd456/0xd789/M/-/-/7/RET/- 0x0/0xd123/-/-/-/0//-\n"
+                         "  4567  0xf002/0xf003/MN/-/-/8/COND/- 0x0/0xf001/-/-/-/0//-\n"
+                         "  4567  0xc456/0xc789/P/-/-/13/-/- 0x0/0xc123/-/-/-/0//-\n";
+
+  // ExpectedSamples contains the aggregated information about
+  // a branch {{From, To, TraceTo}, {TakenCount, MispredCount}}.
+  // If the PBT feture is availabe, an SPE sample has two entries.
+  // These two entries form a chain of two consecutive branches.
+  // However PBT lacks associated information such as branch
+  // source address, branch type, and prediction bit.
+  // For the first branch stack, please see the description above.
+  // Consider this example for PBT trace: {{0x0, 0xc123, 0xc456}, {2, 0}}.
+  // This entry has a TakenCount = 2, as we have two samples for
+  // this entry (0x0,d123) in our input. It has MispredsCount = 0,
+  // as it lacks prediction information.
+  // It also has no infromation about source branch address therefore
+  // the 'From' field filled with zero (0x0).
+  // TraceTo = 0xc456, means the execution jumped from 0xc123 to 0xc456.
+  std::vector<std::pair<Trace, TakenBranchInfo>> ExpectedSamples = {
+      {{0xa002, 0xa003, Trace::BR_ONLY}, {1, 0}}, {{0x0, 0xa001, 0xa002}, {1, 0}},
+      {{0xb002, 0xb003, Trace::BR_ONLY}, {1, 0}}, {{0x0, 0xb001, 0xb002}, {1, 0}},
+      {{0xc456, 0xc789, Trace::BR_ONLY}, {2, 0}}, {{0x0, 0xc123, 0xc456}, {2, 0}},
+      {{0xd456, 0xd789, Trace::BR_ONLY}, {2, 2}}, {{0x0, 0xd123, 0xd456}, {2, 0}},
+      {{0xe005, 0xe009, Trace::BR_ONLY}, {1, 0}}, {{0x0, 0xe001, 0xe005}, {1, 0}},
+      {{0xf002, 0xf003, Trace::BR_ONLY}, {1, 1}}, {{0x0, 0xf001, 0xf002}, {1, 0}}};
+
+  parseAndCheckBrstackEvents(4567, ExpectedSamples);
+}
+
 #endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/160095