Re: [PATCH v2 08/48] tcg/optimize: Split out fold_call

[Richard Henderson <richard.henderson@linaro.org>]

On 10/20/21 9:05 AM, Alex Bennée wrote:
> 
> Richard Henderson <richard.henderson@linaro.org> writes:
> 
>> Calls are special in that they have a variable number
>> of arguments, and need to be able to clobber globals.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   tcg/optimize.c | 63 ++++++++++++++++++++++++++++++++------------------
>>   1 file changed, 41 insertions(+), 22 deletions(-)
>>
>> diff --git a/tcg/optimize.c b/tcg/optimize.c
>> index fad6f5de1f..74b9aa025a 100644
>> --- a/tcg/optimize.c
>> +++ b/tcg/optimize.c
>> @@ -624,10 +624,42 @@ static void copy_propagate(OptContext *ctx, TCGOp *op,
>>       }
>>   }
>>   
>> +static bool fold_call(OptContext *ctx, TCGOp *op)
>> +{
>> +    TCGContext *s = ctx->tcg;
>> +    int nb_oargs = TCGOP_CALLO(op);
>> +    int nb_iargs = TCGOP_CALLI(op);
>> +    int flags, i;
>> +
>> +    init_arguments(ctx, op, nb_oargs + nb_iargs);
>> +    copy_propagate(ctx, op, nb_oargs, nb_iargs);
>> +
>> +    /* If the function reads or writes globals, reset temp data. */
>> +    flags = tcg_call_flags(op);
>> +    if (!(flags & (TCG_CALL_NO_READ_GLOBALS | TCG_CALL_NO_WRITE_GLOBALS))) {
>> +        int nb_globals = s->nb_globals;
> 
> Aren't we missing a trick here?
> 
> If the helper is going to read global registers we need to ensure any
> temps holding their data is written but we don't need to throw the
> existing temps away if the helper is TCG_CALL_NO_WRITE_GLOBALS?

Hmm, if NO_WRITE_GLOBALS, then yes, we should be able to preserve the information about 
the current contents.  There must be some quirk, though; I just don't recall what it is. 
This patch preserves existing behaviour.


r~