* Denys Vlasenko <[email protected]> wrote:
> Use of a temporary R8 register here seems to be unnecessary.
>
> "push %r8" is a two-byte insn (it needs REX prefix to specify R8),
> "push $0" is two-byte too. It seems just using the latter would be
> no worse.
>
> Thus, code had an unnecessary "xorq %r8,%r8" insn.
> It probably costs nothing in execution time here since we are probably
> limited by store bandwidth at this point, but still.
Note that the 3 fewer instruction in the image also shrink the code by 16 bytes:
arch/x86/entry/entry_64_compat.o:
text data bss dec hex filename
380 0 0 380 17c entry_64_compat.o.before
364 0 0 364 16c entry_64_compat.o.after
because (at least in this defconfig build) one of these functions shrunk below
a
16-byte boundary. So cache footprint got denser.
Thanks,
Ingo
