perf: enable V8 builtins PGO (#50575)

* build: enable V8 builtins PGO

Removes the gn arg that disabled V8 builtins profile-guided optimization
and adds a V8 patch to warn instead of abort when the builtin PGO profile
data does not match. Also strips the PGO-related flags from the generated
mksnapshot_args so they are not passed through to downstream mksnapshot
invocations.

Co-authored-by: Sam Attard <sattard@anthropic.com>

* docs: clarify Node.js async_hooks as reason for promise_hooks flag

Addresses review feedback: the v8_enable_javascript_promise_hooks flag
is set to support Node.js async_hooks, not used directly by Electron.

Co-authored-by: Sam Attard <sattard@anthropic.com>

* chore: update patches

---------

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Sam Attard <sattard@anthropic.com>
Co-authored-by: PatchUp <73610968+patchup[bot]@users.noreply.github.com>

.github/actions/build-electron/action.yml

@@ -125,6 +125,9 @@ runs:
         fi
         sed $SEDOPTION '/.*builtins-pgo/d' out/Default/mksnapshot_args
         sed $SEDOPTION '/--turbo-profiling-input/d' out/Default/mksnapshot_args
+        sed $SEDOPTION '/--reorder-builtins/d' out/Default/mksnapshot_args
+        sed $SEDOPTION '/--warn-about-builtin-profile-data/d' out/Default/mksnapshot_args
+        sed $SEDOPTION '/--abort-on-bad-builtin-profile-data/d' out/Default/mksnapshot_args
 
         if [ "${{ inputs.target-platform }}" = "win" ]; then
           cd out/Default

build/args/all.gn

@@ -51,9 +51,6 @@ is_cfi = false
 use_qt5 = false
 use_qt6 = false
 
-# Disables the builtins PGO for V8
-v8_builtins_profiling_log_file = ""
-
 # https://chromium.googlesource.com/chromium/src/+/main/docs/dangling_ptr.md
 # TODO(vertedinde): hunt down dangling pointers on Linux
 enable_dangling_raw_ptr_checks = false

patches/v8/.patches

@@ -1,2 +1,3 @@
 chore_allow_customizing_microtask_policy_per_context.patch
 cherry-pick-d5b0cb2acffe.patch
+build_warn_instead_of_abort_on_builtin_pgo_profile_mismatch.patch

patches/v8/build_warn_instead_of_abort_on_builtin_pgo_profile_mismatch.patch

@@ -0,0 +1,35 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Sam Attard <sattard@anthropic.com>
+Date: Sun, 22 Mar 2026 10:51:26 +0000
+Subject: build: warn instead of abort on builtin PGO profile mismatch
+
+Electron sets v8_enable_javascript_promise_hooks = true to support
+Node.js async_hooks (see node/src/env.cc SetPromiseHooks usage:
+https://github.com/nodejs/node/blob/abff716eaccd0c4f4949d1315cb057a45979649d/src/env.cc#L223-L236).
+This flag adds conditional branches to builtins-microtask-queue-gen.cc
+and promise-misc.tq, changing the control-flow graph hash of several
+Promise/async builtins. This invalidates V8's pre-generated PGO profile
+for those builtins (built with Chrome defaults where the flag is off).
+
+Rather than disabling builtins PGO entirely, warn and skip mismatched
+builtins so all other builtins still benefit from PGO.
+
+diff --git a/BUILD.gn b/BUILD.gn
+index 1bb7fc93c104805a3733280929a6759bacd399b4..874d6c94b258ab9e85ca13495912f2b7cb01189e 100644
+--- a/BUILD.gn
++++ b/BUILD.gn
+@@ -2649,9 +2649,11 @@ template("run_mksnapshot") {
+         "--turbo-profiling-input",
+         rebase_path(v8_builtins_profiling_log_file, root_build_dir),
+ 
+-        # Replace this with --warn-about-builtin-profile-data to see the full
+-        # list of builtins with incompatible profiles.
+-        "--abort-on-bad-builtin-profile-data",
++        # Electron: Use warn instead of abort so that builtins whose control
++        # flow is changed by Electron's build flags (e.g. RunMicrotasks via
++        # v8_enable_javascript_promise_hooks) are skipped rather than failing
++        # the build. All other builtins still receive PGO.
++        "--warn-about-builtin-profile-data",
+       ]
+ 
+       if (!v8_enable_builtins_profiling && v8_enable_builtins_reordering) {