Re: RE: [PATCH 9/21]middle-end: implement vectorizable_early_exit for codegen of exit code

[juzhe.zh...@rivai.ai]

Thanks Tamar.

I am not sure whether I am not on the same page with you.

IMHO, ARM SVE will use the final mask = loop mask (generate by WHILE_ULT) & 
conditional mask.
Use that final mask to do the cbranch. Am I right ?

If yes, I leverage that for length and avoid too much codes change in your 
patch.

So, for RVV, the length is pretty same as loop mask in ARM SVE.
For example, suppose n = 4, in ARM SVE, WHILE_ULT (whilelo) generate mask = 
0b11110000000....
Then use that mask to control the operations.

For RVV, is the same, length will be 4, then we will only process the elements 
with index < 4.

For bias, I think that won't be the issue. Currently, BIAS is not used by RVV 
and only used on len_load/len_store for IBM targets.
So, the bias value by default is 0 in all other situations except 
len_load/len_store specifically for IBM.



juzhe.zh...@rivai.ai
 
From: Tamar Christina
Date: 2023-11-30 18:39
To: juzhe.zh...@rivai.ai; gcc-patches
CC: Richard Biener
Subject: RE: [PATCH 9/21]middle-end: implement vectorizable_early_exit for 
codegen of exit code
Hi Juzhe,
 
I’m happy to take the hunks, just that I can’t test it and don’t know the 
specifics of how it lens work.
I still need to read up on it.
 
I tried adding that chunk in, but for the first bit `lens` seems undefined, and 
the second bit it seems `bias` is undefined.
 
I’ll also need what to do for vectorizable_live_operations how to get the first 
element rather than the last.
 
Thanks,
Tamar
 
From: juzhe.zh...@rivai.ai <juzhe.zh...@rivai.ai> 
Sent: Thursday, November 30, 2023 4:48 AM
To: gcc-patches <gcc-patches@gcc.gnu.org>
Cc: Richard Biener <richard.guent...@gmail.com>; Tamar Christina 
<tamar.christ...@arm.com>
Subject: [PATCH 9/21]middle-end: implement vectorizable_early_exit for codegen 
of exit code
 
Hi, Richard and Tamar.
 
I am sorry for bothering you.
Hope you don't mind I give some comments:
 
Can we support partial vector for length ?
 
IMHO, we can do that as follows:
 
bool length_loop_p = LOOP_VINFO_FULLY_WITH_LENGTH_P (loop_vinfo);
 
if (LOOP_VINFO_CAN_USE_PARTIAL_VECTORS_P (loop_vinfo))
  {
    if (direct_internal_fn_supported_p (IFN_VCOND_MASK_LEN, vectype,
                                        OPTIMIZE_FOR_SPEED))
      vect_record_loop_len (loop_vinfo, lens, ncopies, vectype, 1);
    else
      vect_record_loop_mask (loop_vinfo, masks, ncopies, truth_type, NULL);
  }
 
if (length_loop_p)
  {
    tree len = vect_get_loop_len (loop_vinfo, gsi, loop_lens, 1, vectype, 0, 0);
    /* Use VCOND_MASK_LEN (all true, cond, all false, len, bias) to generate
       final mask = i < len + bias ? cond[i] : false.  */
    cond = gimple_build (&cond_gsi, IFN_VCOND_MASK_LEN, truth_type,
                         all true mask, cond, all false mask, len, bias);
  }
else if (masked_loop_p)
  {
    tree mask
      = vect_get_loop_mask (loop_vinfo, gsi, masks, ncopies, truth_type, 0);
    cond
      = prepare_vec_mask (loop_vinfo, TREE_TYPE (mask), mask, cond, &cond_gsi);
  }
 
This is a prototype. Is this idea reasonable to Richi ?
 
Thanks.
 


juzhe.zh...@rivai.ai