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Re: How to find out register information at the beginning of a basic block?

On 05/31/2010 08:17 PM, H.J. Lu wrote:
On Mon, May 31, 2010 at 12:31 PM, Vladimir Makarov<> wrote:
H.J. Lu wrote:

I am working on generating vzeroupper to avoid AVX->SSE transition

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
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.

My impression is hard_regno_nregs tells me that number of
hard registers given machine mode occupy. It doesn't tell me
the live size of a hard register at the beginning of a basic
block. How do I get this information?
If you mean what part of hard register lives, then as I know there is no such infrastructure code. As I remember Ken Zadeck tried to implement something analogous in the old RA. You could try to find this code in archives.

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