PGO fixes and livability improvements for LTO in Firefox on ppc64le Linux. Read web page first! -- https://www.talospace.com/2024/03/firefox-124-on-power.html

firefox-pgo.diff

diff -r ac0e1ee8218f build/moz.configure/lto-pgo.configure
--- a/build/moz.configure/lto-pgo.configure	Tue Feb 20 13:51:00 2024 +0000
+++ b/build/moz.configure/lto-pgo.configure	Sat Feb 24 22:47:17 2024 -0800
@@ -2,17 +2,17 @@
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # PGO
 # ==============================================================
 llvm_profdata = check_prog(
-    "LLVM_PROFDATA", ["llvm-profdata"], allow_missing=True, paths=clang_search_path
+    "LLVM_PROFDATA", ["llvm-profdata-dont-even-think-about-it"], allow_missing=True, paths=clang_search_path
 )
 
 
 @depends_if(llvm_profdata)
 @checking("whether llvm-profdata supports 'order' subcommand")
 def llvm_profdata_order(profdata):
     retcode, _, _ = get_cmd_output(profdata, "order", "--help")
     return retcode == 0
@@ -128,17 +128,17 @@
 @imports("multiprocessing")
 def pgo_flags(
     compiler, linker, target, profdata, orderfile, target_is_windows, pgo_temporal
 ):
     if compiler.type == "gcc":
         return namespace(
             gen_cflags=["-fprofile-generate"],
             gen_ldflags=["-fprofile-generate"],
-            use_cflags=["-fprofile-use", "-fprofile-correction", "-Wcoverage-mismatch"],
+            use_cflags=["-fprofile-use", "-fprofile-correction", "-Wno-coverage-mismatch"],
             use_ldflags=["-fprofile-use"],
         )
 
     if compiler.type in ("clang-cl", "clang"):
         prefix = ""
         if compiler.type == "clang-cl":
             prefix = "/clang:"
             gen_ldflags = None
diff -r ac0e1ee8218f build/pgo/profileserver.py
--- a/build/pgo/profileserver.py	Tue Feb 20 13:51:00 2024 +0000
+++ b/build/pgo/profileserver.py	Sat Feb 24 22:47:17 2024 -0800
@@ -93,19 +93,32 @@
         ),
         path_mappings=path_mappings,
     )
     sp3_httpd.start(block=False)
     print("started SP3 server on port 8000")
     locations = ServerLocations()
     locations.add_host(host="127.0.0.1", port=PORT, options="primary,privileged")
 
-    old_profraw_files = glob.glob("*.profraw")
-    for f in old_profraw_files:
-        os.remove(f)
+    using_gcc = False
+    try:
+        if build.config_environment.substs.get('CC_TYPE') == 'gcc':
+            using_gcc = True
+    except BuildEnvironmentNotFoundException:
+        pass
+
+    if using_gcc:
+        for dirpath, _, filenames in os.walk('.'):
+            for f in filenames:
+                if f.endswith('.gcda'):
+                    os.remove(os.path.join(dirpath, f))
+    else:
+        old_profraw_files = glob.glob('*.profraw')
+        for f in old_profraw_files:
+            os.remove(f)
 
     with TemporaryDirectory() as profilePath:
         # TODO: refactor this into mozprofile
         profile_data_dir = os.path.join(build.topsrcdir, "testing", "profiles")
         with open(os.path.join(profile_data_dir, "profiles.json"), "r") as fh:
             base_profiles = json.load(fh)["profileserver"]
 
         prefpaths = [
@@ -222,16 +235,20 @@
 
         # Try to move the crash reports to the artifacts even if Firefox appears
         # to exit successfully, in case there's a crash that doesn't set the
         # return code to non-zero for some reason.
         if get_crashreports(profilePath, name="Firefox exited successfully?") != 0:
             print("Firefox exited successfully, but produced a crashreport")
             sys.exit(1)
 
+        print('Copying profile data....')
+        os.system('pwd');
+        os.system('tar cf profdata.tar.gz `find . -name "*.gcda"`; cd ..; tar xf instrumented/profdata.tar.gz;');
+
         llvm_profdata = env.get("LLVM_PROFDATA")
         if llvm_profdata:
             profraw_files = glob.glob("*.profraw")
             if not profraw_files:
                 print(
                     "Could not find profraw files in the current directory: %s"
                     % os.getcwd()
                 )
diff -r ac0e1ee8218f toolkit/components/terminator/nsTerminator.cpp
--- a/toolkit/components/terminator/nsTerminator.cpp	Tue Feb 20 13:51:00 2024 +0000
+++ b/toolkit/components/terminator/nsTerminator.cpp	Sat Feb 24 22:47:17 2024 -0800
@@ -455,16 +455,21 @@
       // Defend against overflow
       crashAfterMS = INT32_MAX;
     } else {
       crashAfterMS *= scaleUp;
     }
   }
 #endif
 
+  // Disable watchdog for PGO train builds - writting profile information at
+  // exit may take time and it is better to make build hang rather than
+  // silently produce poorly performing binary.
+  crashAfterMS = INT32_MAX;
+
   UniquePtr<Options> options(new Options());
   // crashAfterTicks is guaranteed to be > 0 as
   // crashAfterMS >= ADDITIONAL_WAIT_BEFORE_CRASH_MS >> HEARTBEAT_INTERVAL_MS
   options->crashAfterTicks = crashAfterMS / HEARTBEAT_INTERVAL_MS;
 
   DebugOnly<PRThread*> watchdogThread =
       CreateSystemThread(RunWatchdog, options.release());
   MOZ_ASSERT(watchdogThread);

Seems to be handcrafted since there's a duplicate line:

[firefox-117.0]$ patch -Np1 -i firefox-pgo.diff
patching file build/moz.configure/lto-pgo.configure
patch: **** malformed patch at line 5: @@ -81,17 +81,17 @@

Thanks, edited