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Subject[PATCH v2] Kconfig: default to CC_OPTIMIZE_FOR_PERFORMANCE_O3 for gcc >= 10
Date
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@vger.kernel.org
Cc: x86@kernel.org
Cc: stable@vger.kernel.org
Cc: hjl.tools@gmail.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Oleksandr Natalenko <oleksandr@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Laight <David.Laight@aculab.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.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
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