[PATCH 2/5] -march=native: POPCNT support

[Alexey Dobriyan <adobriyan@gmail.com>]

Mainline kernel can only generate "popcnt rax, rdi" instruction
with alternative masquareading as function call. Patch allows
to generate all POPCNT variations and inlines hweigth*() family of functions.

	$ objdump  -dr ../obj/vmlinux | grep popcnt
	ffffffff81004f6d:       f3 48 0f b8 c9          popcnt rcx,rcx
	ffffffff81008484:       f3 48 0f b8 03          popcnt rax,QWORD PTR [rbx]
	ffffffff81073aae:       f3 48 0f b8 d8          popcnt rbx,rax
		...

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
 arch/x86/include/asm/arch_hweight.h | 32 ++++++++++++++++++++++++++++++--
 arch/x86/lib/Makefile               |  5 ++++-
 include/linux/bitops.h              |  2 ++
 lib/Makefile                        |  2 ++
 scripts/kconfig/cpuid.c             |  6 ++++++
 scripts/march-native.sh             |  6 +++++-
 6 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index 34a10b2d5b73..58e4f65d8665 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -2,6 +2,34 @@
 #ifndef _ASM_X86_HWEIGHT_H
 #define _ASM_X86_HWEIGHT_H
 
+#define __HAVE_ARCH_SW_HWEIGHT
+
+#ifdef CONFIG_MARCH_NATIVE_POPCNT
+static inline unsigned int __arch_hweight64(uint64_t x)
+{
+	uint64_t rv;
+	asm ("popcnt %1, %0" : "=r" (rv) : "rm" (x));
+	return rv;
+}
+
+static inline unsigned int __arch_hweight32(uint32_t x)
+{
+	uint32_t rv;
+	asm ("popcnt %1, %0" : "=r" (rv) : "rm" (x));
+	return rv;
+}
+
+static inline unsigned int __arch_hweight16(uint16_t x)
+{
+	return __arch_hweight32(x);
+}
+
+static inline unsigned int __arch_hweight8(uint8_t x)
+{
+	return __arch_hweight32(x);
+}
+#else
+
 #include <asm/cpufeatures.h>
 
 #ifdef CONFIG_64BIT
@@ -18,8 +46,6 @@
 #define REG_OUT "a"
 #endif
 
-#define __HAVE_ARCH_SW_HWEIGHT
-
 static __always_inline unsigned int __arch_hweight32(unsigned int w)
 {
 	unsigned int res;
@@ -61,3 +87,5 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)
 #endif /* CONFIG_X86_32 */
 
 #endif
+
+#endif
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 7b181b61170e..c26ad76e7048 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -27,7 +27,10 @@ lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o
 lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
 
-obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o
+obj-y += msr.o msr-reg.o msr-reg-export.o
+ifneq ($(CONFIG_MARCH_NATIVE),y)
+	obj-y += hweight.o
+endif
 
 ifeq ($(CONFIG_X86_32),y)
         obj-y += atomic64_32.o
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 4cac4e1a72ff..ab58fed4ab90 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -26,10 +26,12 @@
 	(((~0ULL) - (1ULL << (l)) + 1) & \
 	 (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
 
+#ifndef CONFIG_MARCH_NATIVE_POPCNT
 extern unsigned int __sw_hweight8(unsigned int w);
 extern unsigned int __sw_hweight16(unsigned int w);
 extern unsigned int __sw_hweight32(unsigned int w);
 extern unsigned long __sw_hweight64(__u64 w);
+#endif
 
 /*
  * Include this here because some architectures need generic_ffs/fls in
diff --git a/lib/Makefile b/lib/Makefile
index d11c48ec8ffd..3867b73721aa 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -81,7 +81,9 @@ obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o
 obj-$(CONFIG_CHECK_SIGNATURE) += check_signature.o
 obj-$(CONFIG_DEBUG_LOCKING_API_SELFTESTS) += locking-selftest.o
 
+ifneq ($(CONFIG_MARCH_NATIVE_POPCNT),y)
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
+endif
 
 obj-$(CONFIG_BTREE) += btree.o
 obj-$(CONFIG_INTERVAL_TREE) += interval_tree.o
diff --git a/scripts/kconfig/cpuid.c b/scripts/kconfig/cpuid.c
index f1983027fe2b..e565dd446bdf 100644
--- a/scripts/kconfig/cpuid.c
+++ b/scripts/kconfig/cpuid.c
@@ -42,6 +42,8 @@ static inline void cpuid2(uint32_t eax0, uint32_t ecx0, uint32_t *eax, uint32_t
 	);
 }
 
+static bool popcnt	= false;
+
 static uint32_t eax0_max;
 
 static void intel(void)
@@ -51,6 +53,9 @@ static void intel(void)
 	if (eax0_max >= 1) {
 		cpuid(1, &eax, &ecx, &edx, &ebx);
 //		printf("%08x %08x %08x %08x\n", eax, ecx, edx, ebx);
+
+		if (ecx & (1 << 23))
+			popcnt = true;
 	}
 }
 
@@ -70,6 +75,7 @@ int main(int argc, char *argv[])
 		intel();
 
 #define _(x)	if (streq(opt, #x)) return x ? EXIT_SUCCESS : EXIT_FAILURE
+	_(popcnt);
 #undef _
 
 	return EXIT_FAILURE;
diff --git a/scripts/march-native.sh b/scripts/march-native.sh
index 4f0fc82f7722..6641e356b646 100755
--- a/scripts/march-native.sh
+++ b/scripts/march-native.sh
@@ -29,6 +29,10 @@ option() {
 	echo "#define $1 1"	>>"$AUTOCONF2"
 }
 
+if test -x "$CPUID"; then
+	"$CPUID" popcnt		&& option "CONFIG_MARCH_NATIVE_POPCNT"
+fi
+
 if test ! -f "$AUTOCONF1" -o ! -f "$AUTOCONF2"; then
 	exit 0
 fi
@@ -72,7 +76,7 @@ for i in $COLLECT_GCC_OPTIONS; do
 		-mmmx)		option "CONFIG_MARCH_NATIVE_MMX"	;;
 		-mmovbe)	option "CONFIG_MARCH_NATIVE_MOVBE"	;;
 		-mpclmul)	option "CONFIG_MARCH_NATIVE_PCLMUL"	;;
-		-mpopcnt)	option "CONFIG_MATCH_NATIVE_POPCNT"	;;
+		-mpopcnt);;
 		-mprfchw)	option "CONFIG_MARCH_NATIVE_PREFETCHW"	;;
 		-mrdrnd)	option "CONFIG_MARCH_NATIVE_RDRND"	;;
 		-mrdseed)	option "CONFIG_MARCH_NATIVE_RDSEED"	;;
-- 
2.13.6