Commit 8616045f authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

powerpc/bpf/32: Optimise some particular const operations 



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: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e53b1f4a4150ec6cabcaeeef82bf9c361b5f9204.1675245773.git.christophe.leroy@csgroup.eu
parent d3921cbb

arch/powerpc/net/bpf_jit_comp32.c

+20 −3
Original line number Diff line number Diff line
@@ -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;



			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)