linux-kernel - [PATCH 02/17] x86, lto: Disable fancy hweight optimizations for LTO v2

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Message-Id: <1391846481-31491-2-git-send-email-ak@linux.intel.com>
Date:	Sat,  8 Feb 2014 09:01:06 +0100
From:	Andi Kleen <ak@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-kbuild@...r.kernel.org, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 02/17] x86, lto: Disable fancy hweight optimizations for LTO v2

The fancy x86 hweight uses different compiler options for the
hweight file. This does not work with LTO. Just disable the optimization
with LTO

v2: Simplify Kconfig checks (Jan Beulich)
Cc: x86@...nel.org
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/Kconfig                    | 1 +
 arch/x86/include/asm/arch_hweight.h | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 940e50e..f125c5f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -255,6 +255,7 @@ config X86_32_LAZY_GS
 
 config ARCH_HWEIGHT_CFLAGS
 	string
+	default "" if LTO
 	default "-fcall-saved-ecx -fcall-saved-edx" if X86_32
 	default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10 -fcall-saved-r11" if X86_64
 
diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index 9686c3d..ca80549 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -25,9 +25,14 @@ static inline unsigned int __arch_hweight32(unsigned int w)
 {
 	unsigned int res = 0;
 
+#ifdef CONFIG_LTO
+	res  = __sw_hweight32(w);
+#else
+
 	asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT)
 		     : "="REG_OUT (res)
 		     : REG_IN (w));
+#endif
 
 	return res;
 }
@@ -46,6 +51,9 @@ static inline unsigned long __arch_hweight64(__u64 w)
 {
 	unsigned long res = 0;
 
+#ifdef CONFIG_LTO
+	res = __sw_hweight64(w);
+#else
 #ifdef CONFIG_X86_32
 	return  __arch_hweight32((u32)w) +
 		__arch_hweight32((u32)(w >> 32));
@@ -54,6 +62,7 @@ static inline unsigned long __arch_hweight64(__u64 w)
 		     : "="REG_OUT (res)
 		     : REG_IN (w));
 #endif /* CONFIG_X86_32 */
+#endif
 
 	return res;
 }
-- 
1.8.5.2

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