This patch optimizes the code generated by emit_a32_arsh_r64, which handles the BPF_ALU64 BPF_ARSH BPF_X instruction. The original code uses a conditional B followed by an unconditional ORR. The optimization saves one instruction by removing the B instruction and using a conditional ORR (with an inverted condition). Example of the code generated for BPF_ALU64_REG(BPF_ARSH, BPF_REG_0, BPF_REG_1), before optimization: 34: rsb ip, r2, #32 38: subs r9, r2, #32 3c: lsr lr, r0, r2 40: orr lr, lr, r1, lsl ip 44: bmi 0x4c 48: orr lr, lr, r1, asr r9 4c: asr ip, r1, r2 50: mov r0, lr 54: mov r1, ip and after optimization: 34: rsb ip, r2, #32 38: subs r9, r2, #32 3c: lsr lr, r0, r2 40: orr lr, lr, r1, lsl ip 44: orrpl lr, lr, r1, asr r9 48: asr ip, r1, r2 4c: mov r0, lr 50: mov r1, ip Tested on QEMU using lib/test_bpf and test_verifier. Co-developed-by: Xi Wang <xi.wang@xxxxxxxxx> Signed-off-by: Xi Wang <xi.wang@xxxxxxxxx> Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx> --- arch/arm/net/bpf_jit_32.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c index bf85d6db4931..48b89211ee5c 100644 --- a/arch/arm/net/bpf_jit_32.c +++ b/arch/arm/net/bpf_jit_32.c @@ -860,8 +860,8 @@ static inline void emit_a32_arsh_r64(const s8 dst[], const s8 src[], emit(ARM_SUBS_I(tmp2[0], rt, 32), ctx); emit(ARM_MOV_SR(ARM_LR, rd[1], SRTYPE_LSR, rt), ctx); emit(ARM_ORR_SR(ARM_LR, ARM_LR, rd[0], SRTYPE_ASL, ARM_IP), ctx); - _emit(ARM_COND_MI, ARM_B(0), ctx); - emit(ARM_ORR_SR(ARM_LR, ARM_LR, rd[0], SRTYPE_ASR, tmp2[0]), ctx); + _emit(ARM_COND_PL, + ARM_ORR_SR(ARM_LR, ARM_LR, rd[0], SRTYPE_ASR, tmp2[0]), ctx); emit(ARM_MOV_SR(ARM_IP, rd[0], SRTYPE_ASR, rt), ctx); arm_bpf_put_reg32(dst_lo, ARM_LR, ctx); -- 2.17.1
