bpf, riscv: Optimize BPF_JMP BPF_K when imm == 0 on RV64

This patch adds an optimization to BPF_JMP (32- and 64-bit) BPF_K for
when the BPF immediate is zero.

When the immediate is zero, the code can directly use the RISC-V zero
register instead of loading a zero immediate to a temporary register
first.

Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Björn Töpel <bjorn.topel@gmail.com>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Link: https://lore.kernel.org/bpf/20200506000320.28965-4-luke.r.nels@gmail.com

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index c3ce9a911b66719961ddf026d11a9bb351edf1f9..b07cef952019a6320ba8d4a164eca9d281125929 100644 (file)
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -796,7 +796,13 @@ out_be:
        case BPF_JMP32 | BPF_JSET | BPF_K:
                rvoff = rv_offset(i, off, ctx);
                s = ctx->ninsns;
-               emit_imm(RV_REG_T1, imm, ctx);
+               if (imm) {
+                       emit_imm(RV_REG_T1, imm, ctx);
+                       rs = RV_REG_T1;
+               } else {
+                       /* If imm is 0, simply use zero register. */
+                       rs = RV_REG_ZERO;
+               }
                if (!is64) {
                        if (is_signed_bpf_cond(BPF_OP(code)))
                                emit_sext_32_rd(&rd, ctx);
@@ -811,11 +817,10 @@ out_be:
                if (BPF_OP(code) == BPF_JSET) {
                        /* Adjust for and */
                        rvoff -= 4;
-                       emit(rv_and(RV_REG_T1, rd, RV_REG_T1), ctx);
-                       emit_branch(BPF_JNE, RV_REG_T1, RV_REG_ZERO, rvoff,
-                                   ctx);
+                       emit(rv_and(rs, rd, rs), ctx);
+                       emit_branch(BPF_JNE, rs, RV_REG_ZERO, rvoff, ctx);
                } else {
-                       emit_branch(BPF_OP(code), rd, RV_REG_T1, rvoff, ctx);
+                       emit_branch(BPF_OP(code), rd, rs, rvoff, ctx);
                }
                break;