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From:   Arnd Bergmann <arnd@kernel.org>
To:     Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Miguel Ojeda <ojeda@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marco Elver <elver@google.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Randy Dunlap <rdunlap@infradead.org>,
        clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org
Subject: [PATCH] linux/compiler-clang.h: define HAVE_BUILTIN_BSWAP*
Date:   Thu, 25 Feb 2021 17:45:09 +0100
Message-Id: <20210225164513.3667778-1-arnd@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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From: Arnd Bergmann <arnd@arndb.de>

Separating compiler-clang.h from compiler-gcc.h inadventently dropped the
definitions of the three HAVE_BUILTIN_BSWAP macros, which requires falling
back to the open-coded version and hoping that the compiler detects it.

Since all versions of clang support the __builtin_bswap interfaces,
add back the flags and have the headers pick these up automatically.

This results in a 4% improvement of compilation speed for arm defconfig.

Fixes: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/linux/compiler-clang.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 6478bff6fcc2..bbfa9ff6a2ec 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -33,6 +33,16 @@
 #define __no_sanitize_thread
 #endif
 
+/*
+ * sparse (__CHECKER__) pretends to be gcc, but can't do constant
+ * folding in __builtin_bswap*() (yet), so don't set these for it.
+ */
+#if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) && !defined(__CHECKER__)
+#define __HAVE_BUILTIN_BSWAP32__
+#define __HAVE_BUILTIN_BSWAP64__
+#define __HAVE_BUILTIN_BSWAP16__
+#endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP && !__CHECKER__ */
+
 #if __has_feature(undefined_behavior_sanitizer)
 /* GCC does not have __SANITIZE_UNDEFINED__ */
 #define __no_sanitize_undefined \
-- 
2.29.2