Re: [Qemu-devel] [PATCH 2/9] target-arm: A64: add support for ldp (load pair)

[Richard Henderson <rth@twiddle.net>]

On 12/09/2013 10:12 AM, Peter Maydell wrote:
> +static void do_gpr_ld(DisasContext *s, TCGv_i64 dest, TCGv_i64 tcg_addr,
> +                      int size, bool is_signed, bool extend)
> +{
> +    switch (size) {
> +    case 0:
> +        if (is_signed) {
> +            tcg_gen_qemu_ld8s(dest, tcg_addr, get_mem_index(s));
> +        } else {
> +            tcg_gen_qemu_ld8u(dest, tcg_addr, get_mem_index(s));
> +        }
> +        break;
> +    case 1:
> +        if (is_signed) {
> +            tcg_gen_qemu_ld16s(dest, tcg_addr, get_mem_index(s));
> +        } else {
> +            tcg_gen_qemu_ld16u(dest, tcg_addr, get_mem_index(s));
> +        }
> +        break;
> +    case 2:
> +        if (is_signed) {
> +            tcg_gen_qemu_ld32s(dest, tcg_addr, get_mem_index(s));
> +        } else {
> +            tcg_gen_qemu_ld32u(dest, tcg_addr, get_mem_index(s));
> +        }
> +        break;
> +    case 3:
> +        tcg_gen_qemu_ld64(dest, tcg_addr, get_mem_index(s));
> +        break;

Likewise, combine all of this with tcg_gen_qemu_ld_i64.

> +    if (extend && is_signed) {
> +        g_assert(size < 3);
> +        tcg_gen_ext32u_i64(dest, dest);
> +    }

Is it worth noticing in size==2 && !extend that is_signed can be forced false
to avoid the extra extension.

> +static void handle_ldp(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 idx = extract32(insn, 23, 3);
> +    bool is_signed = false;
> +    bool is_vector = extract32(insn, 26, 1);
> +    int opc = extract32(insn, 30, 2);
> +    int size;
> +    bool postindex = true;
> +    bool wback = false;
> +
> +    TCGv_i64 tcg_rt = cpu_reg(s, rt);
> +    TCGv_i64 tcg_rt2 = cpu_reg(s, rt2);
> +    TCGv_i64 tcg_addr;
> +
> +    if (opc == 3) {
> +        unallocated_encoding(s);
> +        return;
> +    }
> +    if (is_vector) {
> +        size = 2 + opc;
> +    } else {
> +        is_signed = opc & 1;
> +        size = 2 + extract32(opc, 1, 1);
> +    }
> +
> +    switch (idx) {
> +    case 1: /* post-index */
> +        postindex = true;
> +        wback = true;
> +        break;
> +    case 2: /* signed offset, rn not updated */
> +        postindex = false;
> +        break;
> +    case 3: /* STP (pre-index) */
> +        postindex = false;
> +        wback = true;
> +        break;
> +    default: /* Failed decoder tree? */
> +        unallocated_encoding(s);
> +        break;
> +    }
> +
> +    offset <<= size;
> +
> +    if (rn == 31) {
> +        gen_check_sp_alignment(s);
> +    }
> +
> +    tcg_addr = tcg_temp_new_i64();
> +    tcg_gen_mov_i64(tcg_addr, cpu_reg_sp(s, rn));
> +
> +    if (!postindex) {
> +        tcg_gen_addi_i64(tcg_addr, tcg_addr, offset);
> +    }
> +
> +    if (is_vector) {
> +        do_fp_ld(s, rt, tcg_addr, size);
> +    } else {
> +        do_gpr_ld(s, tcg_rt, tcg_addr, size, is_signed, false);
> +    }
> +    tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
> +    if (is_vector) {
> +        do_fp_ld(s, rt2, tcg_addr, size);
> +    } else {
> +        do_gpr_ld(s, tcg_rt2, tcg_addr, size, is_signed, false);
> +    }
> +
> +    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);
> +        }
> +        tcg_gen_mov_i64(cpu_reg_sp(s, rn), tcg_addr);
> +    }
> +    tcg_temp_free_i64(tcg_addr);
> +}

There's so much overlap with STP, I think these ought not be separate
functions.  Just merge the middle bit where the actual load/store happens.


r~