On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote:
> On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches <[email protected]> wrote:
> > Is there any value in reordering these tests for frequency
> > or maybe using | instead of || to avoid multiple jumps?
>
> probably not. It's not a critical path.
> compiler may fuse conditions depending on values anyway.
> If it was a critical path, we could have used
> (1 << reg) & mask trick.
> I picked explicit 'return true' else 'return false' here,
> because it felt easier to read. Just a matter of taste.
There is a size difference though: (allyesconfig)
$ size arch/x86/net/built-in.o*
text data bss dec hex filename
12999 1012 4336 18347 47ab arch/x86/net/built-in.o.new
13177 1076 4592 18845 499d arch/x86/net/built-in.o.old
---
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 3f62734..09e2cea 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -135,11 +135,11 @@ static const int reg2hex[] = {
*/
static inline bool is_ereg(u32 reg)
{
- if (reg == BPF_REG_5 || reg == AUX_REG ||
- (reg >= BPF_REG_7 && reg <= BPF_REG_9))
- return true;
- else
- return false;
+ return (1 << reg) & (BIT(BPF_REG_5) |
+ BIT(AUX_REG) |
+ BIT(BPF_REG_7) |
+ BIT(BPF_REG_8) |
+ BIT(BPF_REG_9));
}
/* add modifiers if 'reg' maps to x64 registers r8..r15 */
--
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