[PATCH v1 08/10] powerpc/bpf/32: Optimise some particular const operations

From: Christophe Leroy
Date: Thu Dec 01 2022 - 02:58:16 EST


Simplify multiplications and divisions with constants when the
constant is 1 or -1.

When the constant is a power of 2, replace them by bit shits.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/net/bpf_jit_comp32.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index 6c45d953d4e8..e6e156c0c5d6 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -391,7 +391,13 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
EMIT(PPC_RAW_MULW(dst_reg, dst_reg, src_reg));
break;
case BPF_ALU | BPF_MUL | BPF_K: /* (u32) dst *= (u32) imm */
- if (imm >= -32768 && imm < 32768) {
+ if (imm == 1)
+ break;
+ if (imm == -1) {
+ EMIT(PPC_RAW_SUBFIC(dst_reg, dst_reg, 0));
+ } else if (is_power_of_2((u32)imm)) {
+ EMIT(PPC_RAW_SLWI(dst_reg, dst_reg, ilog2(imm)));
+ } else if (imm >= -32768 && imm < 32768) {
EMIT(PPC_RAW_MULI(dst_reg, dst_reg, imm));
} else {
PPC_LI32(_R0, imm);
@@ -411,6 +417,13 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
EMIT(PPC_RAW_SUBFZE(dst_reg_h, dst_reg_h));
break;
}
+ if (imm > 0 && is_power_of_2(imm)) {
+ imm = ilog2(imm);
+ EMIT(PPC_RAW_RLWINM(dst_reg_h, dst_reg_h, imm, 0, 31 - imm));
+ EMIT(PPC_RAW_RLWIMI(dst_reg_h, dst_reg, imm, 32 - imm, 31));
+ EMIT(PPC_RAW_SLWI(dst_reg, dst_reg, imm));
+ break;
+ }
bpf_set_seen_register(ctx, tmp_reg);
PPC_LI32(tmp_reg, imm);
EMIT(PPC_RAW_MULW(dst_reg_h, dst_reg_h, tmp_reg));
@@ -438,8 +451,12 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
if (imm == 1)
break;

- PPC_LI32(_R0, imm);
- EMIT(PPC_RAW_DIVWU(dst_reg, dst_reg, _R0));
+ if (is_power_of_2((u32)imm)) {
+ EMIT(PPC_RAW_SRWI(dst_reg, dst_reg, ilog2(imm)));
+ } else {
+ PPC_LI32(_R0, imm);
+ EMIT(PPC_RAW_DIVWU(dst_reg, dst_reg, _R0));
+ }
break;
case BPF_ALU | BPF_MOD | BPF_K: /* (u32) dst %= (u32) imm */
if (!imm)
--
2.38.1