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Re: How to find out register information at the beginning of a basic block?
On Mon, May 31, 2010 at 12:31 PM, Vladimir Makarov <vmakarov@redhat.com> wrote:
> H.J. Lu wrote:
>>
>> Hi,
>>
>> I am working on generating vzeroupper to avoid AVX->SSE transition
>> penalty.
>>
>> I have generated vzeroupper on function return as well as function
>> call. ?I am working on a backend pass to eliminate those vzeroupper
>> instructions when I can prove that the upper 128bits of AVX registers
>> are dead at the point where vzeroupper is added. To do that, I need
>> to find out if a register is live at the beginning of a basic block as
>> well
>> as its size. I thought dataflow might give me such info. But I couldn't
>> find a way to access such information. Does anyone have any pointers?
>>
>>
>
> DF_LR_IN (bb) returns bitmap of livings prseudo regnos.
> DF_LIVE_IN (bb) takes availability info into account.
>
> Size of hard registers is defined by hard_regno_nregs.
>
> It is more complicated if you need the size of pseudo. ?The class of pseudo
> is necessary for this but even if you know this there are complicated
> situations, e.g.
The new backend pass is run as the last pass and doesn't deal with pseudo
registers. I have
df_chain_add_problem (DF_UD_CHAIN + DF_DU_CHAIN); <<< Is this correct?
df_analyze ();
FOR_EACH_BB (curr_block)
{
bool upper_128bits_live = false;
bitmap live_in = DF_LIVE_IN (curr_block);
...
}
df_finish_pass (false);
> on x86 pseudo of FLOAT_INT_REGS in DFmode cant take 2 general registers and
> 1 float reg.
>
Thanks.
--
H.J.