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>

1 files changed, 4 insertions, 5 deletions

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 75d3776123cc..a624dcc4de10 100644
--- 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;
 }