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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>
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1 changed files with 4 additions and 5 deletions
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@ -23,13 +23,13 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
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asm volatile(
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" testq %[size8],%[size8]\n"
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" jz 4f\n"
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"0: movq %[zero],(%[dst])\n"
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" addq %[eight],%[dst]\n"
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"0: movq $0,(%[dst])\n"
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" addq $8,%[dst]\n"
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" decl %%ecx ; jnz 0b\n"
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"4: movq %[size1],%%rcx\n"
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" testl %%ecx,%%ecx\n"
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" jz 2f\n"
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"1: movb %b[zero],(%[dst])\n"
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"1: movb $0,(%[dst])\n"
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" incq %[dst]\n"
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" decl %%ecx ; jnz 1b\n"
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"2:\n"
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@ -40,8 +40,7 @@ unsigned long __clear_user(void __user *addr, unsigned long size)
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_ASM_EXTABLE(0b,3b)
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_ASM_EXTABLE(1b,2b)
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: [size8] "=&c"(size), [dst] "=&D" (__d0)
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: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr),
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[zero] "r" (0UL), [eight] "r" (8UL));
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: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr));
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clac();
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return size;
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}
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