linux-kernel - [PATCH v2] Kconfig: default to CC_OPTIMIZE_FOR_PERFORMANCE

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Date:   Mon, 11 May 2020 15:57:20 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kbuild@...r.kernel.org, x86@...nel.org,
        stable@...r.kernel.org, hjl.tools@...il.com,
        Peter Zijlstra <peterz@...radead.org>,
        Jakub Jelinek <jakub@...hat.com>,
        Oleksandr Natalenko <oleksandr@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Laight <David.Laight@...lab.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: [PATCH v2] Kconfig: default to CC_OPTIMIZE_FOR_PERFORMANCE_O3 for gcc >= 10

GCC 10 appears to have changed -O2 in order to make compilation time
faster when using -flto, seemingly at the expense of performance, in
particular with regards to how the inliner works. Since -O3 these days
shouldn't have the same set of bugs as 10 years ago, this commit
defaults new kernel compiles to -O3 when using gcc >= 10.

Cc: linux-kbuild@...r.kernel.org
Cc: x86@...nel.org
Cc: stable@...r.kernel.org
Cc: hjl.tools@...il.com
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Jakub Jelinek <jakub@...hat.com>
Cc: Oleksandr Natalenko <oleksandr@...hat.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Laight <David.Laight@...lab.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
Changes v1->v2:
 - [Oleksandr] Remove O3 dependency on ARC.

 init/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 9e22ee8fbd75..f76ec3ccc883 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1245,7 +1245,8 @@ config BOOT_CONFIG
 
 choice
 	prompt "Compiler optimization level"
-	default CC_OPTIMIZE_FOR_PERFORMANCE
+	default CC_OPTIMIZE_FOR_PERFORMANCE_O3 if GCC_VERSION >= 100000
+	default CC_OPTIMIZE_FOR_PERFORMANCE if (GCC_VERSION < 100000 || CC_IS_CLANG)
 
 config CC_OPTIMIZE_FOR_PERFORMANCE
 	bool "Optimize for performance (-O2)"
@@ -1256,7 +1257,6 @@ config CC_OPTIMIZE_FOR_PERFORMANCE
 
 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
 	bool "Optimize more for performance (-O3)"
-	depends on ARC
 	imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED  # avoid false positives
 	help
 	  Choosing this option will pass "-O3" to your compiler to optimize
-- 
2.26.2