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Re: [Qemu-devel] [PATCH v3 07/20] tcg-arm: Fold epilogue into INDEX_op_e
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH v3 07/20] tcg-arm: Fold epilogue into INDEX_op_exit_tb |
Date: |
Thu, 28 Mar 2013 09:12:19 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
On 03/28/2013 09:05 AM, Peter Maydell wrote:
> On 28 March 2013 15:32, Richard Henderson <address@hidden> 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~
- [Qemu-devel] [PATCH v3 02/20] tcg-arm: Handle negated constant arguments to and/sub, (continued)
[Qemu-devel] [PATCH v3 03/20] tcg-arm: Allow constant first argument to sub, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 06/20] tcg-arm: Improve constant generation, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 07/20] tcg-arm: Fold epilogue into INDEX_op_exit_tb, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 08/20] tcg-arm: Implement deposit for armv7, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 09/20] tcg-arm: Implement division instructions, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 10/20] tcg-arm: Use TCG_REG_TMP name for the tcg temporary, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 11/20] tcg-arm: Use R12 for the tcg temporary, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 12/20] tcg-arm: Cleanup multiply subroutines, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 13/20] tcg-arm: Cleanup tcg_out_goto_label, Richard Henderson, 2013/03/28
[Qemu-devel] [PATCH v3 14/20] tcg-arm: Cleanup goto_tb handling, Richard Henderson, 2013/03/28