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