[Xen-devel] [PATCH RFC 3/4] Arm64: further speed-up to hweight{32, 64}()

["Jan Beulich" <JBeulich@xxxxxxxx>]

According to Linux commit e75bef2a4f ("arm64: Select
ARCH_HAS_FAST_MULTIPLIER") this is a further improvement over the
variant using only bitwise operations on at least some hardware, and no
worse on other.

Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC: To be honest I'm not fully convinced this is a win in particular in
     the hweight32() case, as there's no actual shift insn which gets
     replaced by the multiplication. Even for hweight64() the compiler
     could emit better code and avoid the explicit shift by 32 (which it
     emits at least for me).

--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -12,6 +12,7 @@ config ARM_32
 config ARM_64
        def_bool y
        depends on 64BIT
+       select HAS_FAST_MULTIPLY
 
 config ARM
        def_bool y



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