Re: [Qemu-devel] [PATCH 2.3 7/8] tcg: Implement insert_op_before

[Richard Henderson <rth@twiddle.net>]

On 11/14/2014 04:25 PM, Bastian Koppelmann wrote:
> 
> On 11/11/2014 04:24 PM, Richard Henderson wrote:
>> Rather reserving space in the op stream for optimization,
>> let the optimizer add ops as necessary.
>>
>> Signed-off-by: Richard Henderson <rth@twiddle.net>
>> ---
>>   tcg/optimize.c | 57 +++++++++++++++++++++++++++++++++++----------------------
>>   tcg/tcg-op.c   | 16 ----------------
>>   2 files changed, 35 insertions(+), 38 deletions(-)
>>
>> diff --git a/tcg/optimize.c b/tcg/optimize.c
>> index 973fbb4..067917c 100644
>> --- a/tcg/optimize.c
>> +++ b/tcg/optimize.c
>> @@ -67,6 +67,37 @@ static void reset_temp(TCGArg temp)
>>       temps[temp].mask = -1;
>>   }
>>   +static TCGOp *insert_op_before(TCGContext *s, TCGOp *old_op,
>> +                                TCGOpcode opc, int nargs)
>> +{
>> +    int oi = s->gen_next_op_idx;
>> +    int pi = s->gen_next_parm_idx;
>> +    int prev = old_op->prev;
>> +    int next = old_op - s->gen_op_buf;
>> +    TCGOp *new_op;
>> +
>> +    tcg_debug_assert(oi < OPC_BUF_SIZE);
>> +    tcg_debug_assert(pi + nargs <= OPPARAM_BUF_SIZE);
> I thinks it is better to assure these assertion always hold, e.g.
> 
>     if (oi < OPC_BUF_SIZE || pi + nargs <= OPPARAM_BUF_SIZE) {
>         return NULL;
>     }
>     ...
>     TCGOp *op2 = insert_op_before(s, op, INDEX_op_movi_i32, 2);
>     if (op2) {
>         *args2 = &s->gen_opparam_buf[op2->args];
>     }
> 
> Or how do we know they always hold?

For the same reason we don't bother checking during initial generation of the
opcodes.  We simply assume there's enough space.  Not a good answer but...

> All references on tcg_gen_op0 are gone, so lets remove it.

Fair enough.


r~