blitz@inode /boot % cat /proc/version
Linux version 5.4.6-2-ck (linux-ck@archlinux) (clang version 9.0.0 (tags/RELEASE_900/final)) #1 SMP PREEMPT Tue, 24 Dec 2019 18:17:39 +0000

@@ -704,7 +704,7 @@
 KBUILD_CFLAGS   += $(call cc-disable-warning, address-of-packed-member)
 ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
-KBUILD_CFLAGS += -O2
+KBUILD_CFLAGS += -O3
 else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3
 KBUILD_CFLAGS += -O3
 else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE

build() {
  cd linux-${pkgver}
  make CC=clang HOSTCC=clang bzImage modules
}