[llvm-branch-commits] [llvm] [BOLT] Accept PLT fall-throughs as valid traces (PR #129481)

[Amir Ayupov via llvm-branch-commits]

https://github.com/aaupov updated https://github.com/llvm/llvm-project/pull/129481

>From b0da5dc1e277381c3819e1980b97199286f9208d Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov at fb.com>
Date: Mon, 3 Mar 2025 07:20:10 -0800
Subject: [PATCH 1/2] format

Created using spr 1.3.4
---
 bolt/test/link_fdata.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/bolt/test/link_fdata.py b/bolt/test/link_fdata.py
index 4555e6b0479ae..67117a751b32f 100755
--- a/bolt/test/link_fdata.py
+++ b/bolt/test/link_fdata.py
@@ -85,7 +85,9 @@
 
 # Read nm output: <symbol value> <symbol type> <symbol name>
 nm_output = subprocess.run(
-    [args.nmtool, "--defined-only", "--synthetic", args.objfile], text=True, capture_output=True
+    [args.nmtool, "--defined-only", "--synthetic", args.objfile],
+    text=True,
+    capture_output=True,
 ).stdout
 # Populate symbol map
 symbols = {}

>From 8c90ebcba6a4f85087bec2d80047a3c9c00b43a4 Mon Sep 17 00:00:00 2001
From: Amir Ayupov <aaupov at fb.com>
Date: Mon, 3 Mar 2025 10:46:47 -0800
Subject: [PATCH 2/2] updated comment, fix link_fdata

Created using spr 1.3.4
---
 bolt/lib/Profile/DataAggregator.cpp | 9 ++++++---
 bolt/test/link_fdata.py             | 9 ++++++++-
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/bolt/lib/Profile/DataAggregator.cpp b/bolt/lib/Profile/DataAggregator.cpp
index dec82a3c06083..ed66191343a7f 100644
--- a/bolt/lib/Profile/DataAggregator.cpp
+++ b/bolt/lib/Profile/DataAggregator.cpp
@@ -852,9 +852,12 @@ DataAggregator::getFallthroughsInTrace(BinaryFunction &BF,
   if (From > To)
     return std::nullopt;
 
-  // Accept fall-throughs inside pseudo functions (PLT/thunks). Such functions
-  // are marked as ignored and so lack CFG, which means fallthroughs in them are
-  // reported as mismatching traces which they are not.
+  // Accept fall-throughs inside pseudo functions (PLT/thunks).
+  // This check has to be above BF.empty as pseudo functions would pass it:
+  // pseudo => ignored => CFG not built => empty.
+  // If we return nullopt, trace would be reported as mismatching disassembled
+  // function contents which it is not. To avoid this, return an empty
+  // fall-through list instead.
   if (BF.isPseudo())
     return Branches;
 
diff --git a/bolt/test/link_fdata.py b/bolt/test/link_fdata.py
index 67117a751b32f..f1d83458346d6 100755
--- a/bolt/test/link_fdata.py
+++ b/bolt/test/link_fdata.py
@@ -8,6 +8,7 @@
 """
 
 import argparse
+import os
 import subprocess
 import sys
 import re
@@ -84,8 +85,14 @@
             exit("ERROR: unexpected input:\n%s" % line)
 
 # Read nm output: <symbol value> <symbol type> <symbol name>
+is_llvm_nm = os.path.basename(args.nmtool) == "llvm-nm"
 nm_output = subprocess.run(
-    [args.nmtool, "--defined-only", "--synthetic", args.objfile],
+    [
+        args.nmtool,
+        "--defined-only",
+        "--special-syms" if is_llvm_nm else "--synthetic",
+        args.objfile,
+    ],
     text=True,
     capture_output=True,
 ).stdout