From b219e18b91b4279a582abb9195a1fefc5d8838c0 Mon Sep 17 00:00:00 2001
From: Nicholas Junge <nicholas.junge@web.de>
Date: Fri, 27 Oct 2023 13:49:43 +0200
Subject: [PATCH] [bindings] Add LTO builds on Windows+MSVC (#1687)

* Add LTO builds on Windows+MSVC

Gates the MSVC switches behind an `@bazel_skylib:selects` statement.

This is a first experiment from best guesses and studying the MSVC docs.

* Fix misleading inline comment
---
 bindings/python/nanobind.BUILD | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/bindings/python/nanobind.BUILD b/bindings/python/nanobind.BUILD
index c7edfb2b..c6fa1c6d 100644
--- a/bindings/python/nanobind.BUILD
+++ b/bindings/python/nanobind.BUILD
@@ -2,11 +2,21 @@ licenses(["notice"])
 
 package(default_visibility = ["//visibility:public"])
 
+load("@bazel_skylib//lib:selects.bzl", "selects")
+
 config_setting(
     name = "msvc_compiler",
     flag_values = {"@bazel_tools//tools/cpp:compiler": "msvc-cl"},
 )
 
+selects.config_setting_group(
+    name = "winplusmsvc",
+    match_all = [
+        "@platforms//os:windows",
+        ":msvc_compiler",
+    ],
+)
+
 cc_library(
     name = "nanobind",
     srcs = glob([
@@ -20,6 +30,7 @@ cc_library(
         ":msvc_compiler": [
             "/EHsc",  # exceptions
             "/Os",  # size optimizations
+            "/GL",  # LTO / whole program optimization
         ],
         # these should work on both clang and gcc.
         "//conditions:default": [
@@ -33,7 +44,8 @@ cc_library(
         "include",
     ],
     linkopts = select({
-        "@platforms//os:macos": ["-Wl,@$(location :cmake/darwin-ld-cpython.sym)"],
+        ":winplusmsvc": ["/LTGC"],  # Windows + MSVC.
+        "@platforms//os:macos": ["-Wl,@$(location :cmake/darwin-ld-cpython.sym)"],  # Apple.
         "//conditions:default": [],
     }),
     textual_hdrs = glob(