[PATCH bpf-next 16/19] nfp: bpf: optimize codegen for JSET with a constant

[Jakub Kicinski]

The top word of the constant can only have bits set if sign
extension set it to all-1, therefore we don't really have to
mask the top half of the register.  We can just OR it into
the result as is.

Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
Reviewed-by: Quentin Monnet <quentin.mon...@netronome.com>
---
 drivers/net/ethernet/netronome/nfp/bpf/jit.c | 22 +++++++++-----------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c 
b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
index 6e83bd4707fb..054382b9cbe6 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
@@ -3052,21 +3052,19 @@ static int jset_imm(struct nfp_prog *nfp_prog, struct 
nfp_insn_meta *meta)
 {
        const struct bpf_insn *insn = &meta->insn;
        u64 imm = insn->imm; /* sign extend */
+       u8 dst_gpr = insn->dst_reg * 2;
        swreg tmp_reg;
 
-       if (imm & ~0U) {
-               tmp_reg = ur_load_imm_any(nfp_prog, imm & ~0U, imm_b(nfp_prog));
-               emit_alu(nfp_prog, reg_none(),
-                        reg_a(insn->dst_reg * 2), ALU_OP_AND, tmp_reg);
-               emit_br(nfp_prog, BR_BNE, insn->off, 0);
-       }
-
-       if (imm >> 32) {
-               tmp_reg = ur_load_imm_any(nfp_prog, imm >> 32, imm_b(nfp_prog));
+       tmp_reg = ur_load_imm_any(nfp_prog, imm & ~0U, imm_b(nfp_prog));
+       emit_alu(nfp_prog, imm_b(nfp_prog),
+                reg_a(dst_gpr), ALU_OP_AND, tmp_reg);
+       /* Upper word of the mask can only be 0 or ~0 from sign extension,
+        * so either ignore it or OR the whole thing in.
+        */
+       if (imm >> 32)
                emit_alu(nfp_prog, reg_none(),
-                        reg_a(insn->dst_reg * 2 + 1), ALU_OP_AND, tmp_reg);
-               emit_br(nfp_prog, BR_BNE, insn->off, 0);
-       }
+                        reg_a(dst_gpr + 1), ALU_OP_OR, imm_b(nfp_prog));
+       emit_br(nfp_prog, BR_BNE, insn->off, 0);
 
        return 0;
 }
-- 
2.19.2