[PATCHv2, 2/7] ppc: bpf/jit: Fix/enhance 32-bit Load Immediate implementation

Michael Ellerman mpe at ellerman.id.au
Tue Jun 28 22:10:12 AEST 2016

On Wed, 2016-22-06 at 16:25:02 UTC, "Naveen N. Rao" wrote:
> The existing LI32() macro can sometimes result in a sign-extended 32-bit
> load that does not clear the top 32-bits properly. As an example,
> loading 0x7fffffff results in the register containing
> 0xffffffff7fffffff. While this does not impact classic BPF JIT
> implementation (since that only uses the lower word for all operations),
> we would like to share this macro between classic BPF JIT and extended
> BPF JIT, wherein the entire 64-bit value in the register matters. Fix
> this by first doing a shifted LI followed by ORI.
> An additional optimization is with loading values between -32768 to -1,
> where we now only need a single LI.
> The new implementation now generates the same or less number of
> instructions.
> Acked-by: Alexei Starovoitov <ast at kernel.org>
> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>

Series applied to powerpc next, thanks.



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