The following commit has been merged into the locking/kcsan branch of tip: Commit-ID: a5dead405f6be1fb80555bdcb77c406bf133fdc8 Gitweb: https://git.kernel.org/tip/a5dead405f6be1fb80555bdcb77c406bf133fdc8 Author: Marco Elver <el...@google.com> AuthorDate: Wed, 27 May 2020 12:32:36 +02:00 Committer: Borislav Petkov <b...@suse.de> CommitterDate: Wed, 27 May 2020 14:03:26 +02:00
compiler_types.h: Optimize __unqual_scalar_typeof compilation time If the compiler supports C11's _Generic, use it to speed up compilation times of __unqual_scalar_typeof(). GCC version 4.9 or later and all supported versions of Clang support the feature (the oldest supported compiler that doesn't support _Generic is GCC 4.8, for which we use the slower alternative). The non-_Generic variant relies on multiple expansions of __pick_integer_type -> __pick_scalar_type -> __builtin_choose_expr, which increases pre-processed code size, and can cause compile times to increase in files with numerous expansions of READ_ONCE(), or other users of __unqual_scalar_typeof(). Summary of compile-time benchmarking done by Arnd Bergmann: <baseline normalized time> clang-11 gcc-9 this patch 0.78 0.91 ideal 0.76 0.86 See https://lkml.kernel.org/r/CAK8P3a3UYQeXhiufUevz=rwe09wm_vstcd9w+kvjhjcoeqy...@mail.gmail.com Further compile-testing done with: gcc 4.8, 4.9, 5.5, 6.4, 7.5, 8.4; clang 9, 10. Reported-by: Arnd Bergmann <a...@arndb.de> Signed-off-by: Marco Elver <el...@google.com> Signed-off-by: Borislav Petkov <b...@suse.de> Acked-by: Peter Zijlstra <pet...@infradead.org> Tested-by: Arnd Bergmann <a...@arndb.de> Link: https://lkml.kernel.org/r/20200527103236.148700-1-el...@google.com Link: https://lkml.kernel.org/r/CAK8P3a0RJtbVi1JMsfik=jkhcnfv+djn_fedg-ylw+ueqw3...@mail.gmail.com --- include/linux/compiler_types.h | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 5faf68e..a529fa2 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -245,7 +245,9 @@ struct ftrace_likely_data { /* * __unqual_scalar_typeof(x) - Declare an unqualified scalar type, leaving * non-scalar types unchanged. - * + */ +#if defined(CONFIG_CC_IS_GCC) && CONFIG_GCC_VERSION < 40900 +/* * We build this out of a couple of helper macros in a vain attempt to * help you keep your lunch down while reading it. */ @@ -267,6 +269,24 @@ struct ftrace_likely_data { __pick_integer_type(x, int, \ __pick_integer_type(x, long, \ __pick_integer_type(x, long long, x)))))) +#else +/* + * If supported, prefer C11 _Generic for better compile-times. As above, 'char' + * is not type-compatible with 'signed char', and we define a separate case. + */ +#define __scalar_type_to_expr_cases(type) \ + type: (type)0, unsigned type: (unsigned type)0 + +#define __unqual_scalar_typeof(x) typeof( \ + _Generic((x), \ + __scalar_type_to_expr_cases(char), \ + signed char: (signed char)0, \ + __scalar_type_to_expr_cases(short), \ + __scalar_type_to_expr_cases(int), \ + __scalar_type_to_expr_cases(long), \ + __scalar_type_to_expr_cases(long long), \ + default: (x))) +#endif /* Is this type a native word size -- useful for atomic operations */ #define __native_word(t) \
