LoongArch: BPF: Optimize sign-extention mov instructions

For 8-bit and 16-bit sign-extention mov instructions, it can use the native
instructions ext.w.b and ext.w.h directly, no need to use the temporary t1
register, just remove the redundant operations.

Here are the test results:

  # modprobe test_bpf test_range=81,84
  # dmesg -t | tail -5
  test_bpf: #81 ALU_MOVSX | BPF_B jited:1 5 PASS
  test_bpf: #82 ALU_MOVSX | BPF_H jited:1 5 PASS
  test_bpf: #83 ALU64_MOVSX | BPF_B jited:1 5 PASS
  test_bpf: #84 ALU64_MOVSX | BPF_H jited:1 5 PASS
  test_bpf: Summary: 4 PASSED, 0 FAILED, [4/4 JIT'ed]

Signed-off-by: Tiezhu Yang <[email protected]>

Author: seehearfeel

arch/loongarch/net/bpf_jit.c

@@ -527,13 +527,11 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
 			emit_zext_32(ctx, dst, is32);
 			break;
 		case 8:
-			move_reg(ctx, t1, src);
-			emit_insn(ctx, extwb, dst, t1);
+			emit_insn(ctx, extwb, dst, src);
 			emit_zext_32(ctx, dst, is32);
 			break;
 		case 16:
-			move_reg(ctx, t1, src);
-			emit_insn(ctx, extwh, dst, t1);
+			emit_insn(ctx, extwh, dst, src);
 			emit_zext_32(ctx, dst, is32);
 			break;
 		case 32: