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 c3ce9a9..b07cef9 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -796,7 +796,13 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
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 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
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;