x86/asm/64: Micro-optimize __clear_user() - Use immediate constants

Save two registers. Adding constants should be just as fast as adding registers.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180507213937.GB32406@avx2
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 75d3776123cc0f8ee4d79dc2c07e17c431a950dd..a624dcc4de104b2b616338334537a034b6b1da4a 100644 (file)
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -23,13 +23,13 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
        asm volatile(
                "       testq  %[size8],%[size8]\n"
                "       jz     4f\n"
-               "0:     movq %[zero],(%[dst])\n"
-               "       addq   %[eight],%[dst]\n"
+               "0:     movq $0,(%[dst])\n"
+               "       addq   $8,%[dst]\n"
                "       decl %%ecx ; jnz   0b\n"
                "4:     movq  %[size1],%%rcx\n"
                "       testl %%ecx,%%ecx\n"
                "       jz     2f\n"
-               "1:     movb   %b[zero],(%[dst])\n"
+               "1:     movb   $0,(%[dst])\n"
                "       incq   %[dst]\n"
                "       decl %%ecx ; jnz  1b\n"
                "2:\n"
@@ -40,8 +40,7 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
                _ASM_EXTABLE(0b,3b)
                _ASM_EXTABLE(1b,2b)
                : [size8] "=&c"(size), [dst] "=&D" (__d0)
-               : [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr),
-                 [zero] "r" (0UL), [eight] "r" (8UL));
+               : [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
        clac();
        return size;
 }