[RFC 11/12] nfp: bpf: add register rename

[Jakub Kicinski]

If we use resources more wisely we may be able to use
programmable engines in a denser fashion.  Try to squeeze
used registers together.

Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
Reviewed-by: Dinan Gunawardena <dgunaward...@netronome.com>
Reviewed-by: Simon Horman <simon.hor...@netronome.com>
---
 drivers/net/ethernet/netronome/nfp/nfp_bpf_jit.c | 51 +++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/nfp_bpf_jit.c 
b/drivers/net/ethernet/netronome/nfp/nfp_bpf_jit.c
index a83e7404598f..b4dd04f4c653 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_bpf_jit.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_bpf_jit.c
@@ -847,6 +847,42 @@ static void nfp_bpf_opt_reg_init(struct nfp_prog *nfp_prog)
        }
 }
 
+/* Try to rename registers so that program uses only low ones */
+static int nfp_bpf_opt_reg_rename(struct nfp_prog *nfp_prog)
+{
+       bool reg_used[__MAX_BPF_REG] = {};
+       u8 tgt_reg[__MAX_BPF_REG] = {};
+       struct nfp_insn_meta *meta;
+       unsigned int i, j;
+
+       list_for_each_entry(meta, &nfp_prog->insns, l) {
+               if (meta->skip)
+                       continue;
+
+               reg_used[meta->insn.src_reg] = true;
+               reg_used[meta->insn.dst_reg] = true;
+       }
+
+       if (reg_used[BPF_REG_10]) {
+               pr_err("Detected use of stack ptr\n");
+               return -EINVAL;
+       }
+
+       for (i = 0, j = 0; i < ARRAY_SIZE(tgt_reg); i++) {
+               if (!reg_used[i])
+                       continue;
+
+               tgt_reg[i] = j++;
+       }
+
+       list_for_each_entry(meta, &nfp_prog->insns, l) {
+               meta->insn.src_reg = tgt_reg[meta->insn.src_reg];
+               meta->insn.dst_reg = tgt_reg[meta->insn.dst_reg];
+       }
+
+       return 0;
+}
+
 /* Remove masking after load since our load guarantees this is not needed */
 static void nfp_bpf_opt_ld_mask(struct nfp_prog *nfp_prog)
 {
@@ -921,11 +957,20 @@ static void nfp_bpf_opt_ld_shift(struct nfp_prog 
*nfp_prog)
        }
 }
 
-static void nfp_bpf_optimize(struct nfp_prog *nfp_prog)
+static int nfp_bpf_optimize(struct nfp_prog *nfp_prog)
 {
+       int ret;
+
        nfp_bpf_opt_reg_init(nfp_prog);
+
+       ret = nfp_bpf_opt_reg_rename(nfp_prog);
+       if (ret)
+               return ret;
+
        nfp_bpf_opt_ld_mask(nfp_prog);
        nfp_bpf_opt_ld_shift(nfp_prog);
+
+       return 0;
 }
 
 /**
@@ -961,7 +1006,9 @@ nfp_bpf_jit(struct bpf_prog *filter, void *prog_mem, 
unsigned int prog_start,
        if (ret)
                goto out;
 
-       nfp_bpf_optimize(nfp_prog);
+       ret = nfp_bpf_optimize(nfp_prog);
+       if (ret)
+               goto out;
 
        nfp_prog->prog = prog_mem;
        nfp_prog->__prog_alloc_len = prog_sz;
-- 
1.9.1