Re: [Qemu-devel] [PATCH 1/9] target-arm: A64: add support for stp (store pair)

[Richard Henderson <rth@twiddle.net>]

On 12/09/2013 10:12 AM, Peter Maydell wrote:
> +static void do_gpr_st(DisasContext *s, TCGv_i64 source,
> +                      TCGv_i64 tcg_addr, int size)
> +{
> +    switch (size) {
> +    case 0:
> +        tcg_gen_qemu_st8(source, tcg_addr, get_mem_index(s));
> +        break;
> +    case 1:
> +        tcg_gen_qemu_st16(source, tcg_addr, get_mem_index(s));
> +        break;
> +    case 2:
> +        tcg_gen_qemu_st32(source, tcg_addr, get_mem_index(s));
> +        break;
> +    case 3:
> +        tcg_gen_qemu_st64(source, tcg_addr, get_mem_index(s));
> +        break;

Please use the new ldst entry points.  In this case,

  tcg_gen_qemu_st_i64(source, tcg_addr, get_mem_index(s), MO_TE + size)

since size is already log2.

> +static void do_fp_st(DisasContext *s, int srcidx, TCGv_i64 tcg_addr, int size)
> +{
> +    /* This writes the bottom N bits of a 128 bit wide vector to memory */
> +    int freg_offs = offsetof(CPUARMState, vfp.regs[srcidx * 2]);
> +    TCGv_i64 tmp = tcg_temp_new_i64();
> +
> +    switch (size) {
> +    case 0:
> +        tcg_gen_ld8u_i64(tmp, cpu_env, freg_offs);
> +        tcg_gen_qemu_st8(tmp, tcg_addr, get_mem_index(s));
> +        break;
> +    case 1:
> +        tcg_gen_ld16u_i64(tmp, cpu_env, freg_offs);
> +        tcg_gen_qemu_st16(tmp, tcg_addr, get_mem_index(s));
> +        break;
> +    case 2:
> +        tcg_gen_ld32u_i64(tmp, cpu_env, freg_offs);
> +        tcg_gen_qemu_st32(tmp, tcg_addr, get_mem_index(s));
> +        break;
> +    case 3:
> +        tcg_gen_ld_i64(tmp, cpu_env, freg_offs);
> +        tcg_gen_qemu_st64(tmp, tcg_addr, get_mem_index(s));
> +        break;
> +    case 4:
> +    {
> +        TCGv_i64 tcg_hiaddr = tcg_temp_new_i64();
> +        tcg_gen_ld_i64(tmp, cpu_env, freg_offs);
> +        tcg_gen_qemu_st64(tmp, tcg_addr, get_mem_index(s));
> +        tcg_gen_ld_i64(tmp, cpu_env, freg_offs + sizeof(float64));
> +        tcg_gen_addi_i64(tcg_hiaddr, tcg_addr, 8);
> +        tcg_gen_qemu_st64(tmp, tcg_hiaddr, get_mem_index(s));
> +        tcg_temp_free_i64(tcg_hiaddr);
> +        break;
> +    }

You'll certainly have to continue to special-case the 128-bit store, but the
other sizes need not be.

> +/*
> + * C5.6.177 STP (Store Pair - non vector)
> + * C6.3.284 STP (Store Pair of SIMD&FP)
> + *
> + *  31 30 29   27 26  25   23 22 21   15 14   10 9    5 4    0
> + * +-----+-------+---+-------+--+-----------------------------+
> + * | opc | 1 0 1 | V | index | 0|  imm7 |  Rt2  |  Rn  | Rt   |
> + * +-----+-------+---+-------+--+-------+-------+------+------+
> + *
> + * opc: STP           00 -> 32 bit, 10 -> 64 bit
> + *      STP (SIMD&FP) 00 -> 32 bit, 01 -> 64 bit, 10 -> 128 bit
> + * idx: 001 -> post-index, 011 -> pre-index, 010 -> signed off
> + *
> + * Rt, Rt2 = GPR or SIMD registers to be stored
> + * Rn = general purpose register containing address
> + * imm7 = signed offset (multiple of 4 or 8 depending on size)
> + */
> +static void handle_stp(DisasContext *s, uint32_t insn)
> +{
> +    int rt = extract32(insn, 0, 5);
> +    int rn = extract32(insn, 5, 5);
> +    int rt2 = extract32(insn, 10, 5);
> +    int64_t offset = sextract32(insn, 15, 7);
> +    int type = extract32(insn, 23, 2);
> +    bool is_vector = extract32(insn, 26, 1);
> +    int opc = extract32(insn, 30, 2);
> +
> +    TCGv_i64 tcg_rt = cpu_reg(s, rt);
> +    TCGv_i64 tcg_rt2 = cpu_reg(s, rt2);

If you're going to combine vector and non-vector STP, then I think it would be
cleaner if you didn't load these registers so early, when we're not even sure
if we're talking about general registers.

> +    if (wback) {
> +        if (postindex) {
> +            tcg_gen_addi_i64(tcg_addr, tcg_addr, offset - (1 << size));
> +        } else {
> +            tcg_gen_subi_i64(tcg_addr, tcg_addr, 1 << size);
> +        }

Perhaps better as

    tcg_gen_addi_i64(tcg_addr, tcg_addr,
                     (postindex ? offset : 0) - (1 << size));


?


r~