On 03/28/2013 09:05 AM, Peter Maydell wrote:
> On 28 March 2013 15:32, Richard Henderson <r...@twiddle.net> wrote:
>> The epilogue on ARM is one pop instruction, that pops the return
>> address into PC. Avoid the jump to jump for this case. Use the
>> standard movi32 routine for loading the return value if it's easy.
>
>> @@ -2025,8 +2023,7 @@ static void tcg_target_qemu_prologue(TCGContext *s)
>> tcg_out_mov(s, TCG_TYPE_PTR, TCG_AREG0, tcg_target_call_iarg_regs[0]);
>>
>> tcg_out_bx(s, COND_AL, tcg_target_call_iarg_regs[1]);
>> - tb_ret_addr = s->code_ptr;
>>
>> /* ldmia sp!, { r4 - r12, pc } */
>> - tcg_out32(s, (COND_AL << 28) | 0x08bd9ff0);
>> + tb_pop_ret = (COND_AL << 28) | 0x08bd9ff0;
>> }
>
> Why are we using a variable when it's always constant?
I just wanted the comments for the stmia and ldmia to be the same, and near one
another. Would it be better if tcg_target_qemu_prologue was moved up in the
file, and tb_ret_addr made a static const (which the compiler should fold)?
E.g.
/* ldmia sp!, { r4 - r12, pc } @ See the stmia definition below. */
static const uint32_t tb_pop_ret = ...;
static void tcg_target_qemu_prologue(TCGContext *s)
{
/* comment */
/* stmia sp!, {r4-r12, lr} */
tcg_out32(...);
...
}
> Also, please add a comment to the bottom of the qemu_prologue()
> saying something like
>
> /* We never return here; we always return directly from generated
> * code to our caller.
> */
Sure.
r~
