Re: [PATCH] vect: Fold LEN_{LOAD,STORE} if it's for the whole vector [PR107412]

["Kewen.Lin" <linkw@linux.ibm.com>]

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Hi Richard,

on 2022/11/24 17:24, Richard Sandiford wrote:
> "Kewen.Lin" <linkw@linux.ibm.com> writes:
>> Hi,
>>
>> As the test case in PR107412 shows, we can fold IFN .LEN_{LOAD,
>> STORE} into normal vector load/store if the given length is known
>> to be equal to the length of the whole vector.  It would help to
>> improve overall cycles as normally the latency of vector access
>> with length in bytes is bigger than normal vector access, and it
>> also saves the preparation for length if constant length can not
>> be encoded into instruction (such as on power).
>>
>> Bootstrapped and regtested on x86_64-redhat-linux,
>> aarch64-linux-gnu and powerpc64{,le}-linux-gnu.
>>
>> Is it ok for trunk?
>>
>> BR,
>> Kewen
>> -----
>> 	PR tree-optimization/107412
>>
>> gcc/ChangeLog:
>>
>> 	* gimple-fold.cc (gimple_fold_mask_load_store_mem_ref): Rename to ...
>> 	(gimple_fold_partial_load_store_mem_ref): ... this, add one parameter
>> 	mask_p indicating it's for mask or length, and add some handlings for
>> 	IFN LEN_{LOAD,STORE}.
>> 	(gimple_fold_mask_load): Rename to ...
>> 	(gimple_fold_partial_load): ... this, add one parameter mask_p.
>> 	(gimple_fold_mask_store): Rename to ...
>> 	(gimple_fold_partial_store): ... this, add one parameter mask_p.
>> 	(gimple_fold_call): Add the handlings for IFN LEN_{LOAD,STORE},
>> 	and adjust calls on gimple_fold_mask_load_store_mem_ref to
>> 	gimple_fold_partial_load_store_mem_ref.
> 
> Sorry to reply to late (still catching up on email), but:
> 
>>
>> gcc/testsuite/ChangeLog:
>>
>> 	* gcc.target/powerpc/pr107412.c: New test.
>> 	* gcc.target/powerpc/p9-vec-length-epil-8.c: Adjust scan times for
>> 	folded LEN_LOAD.
>> ---
>>  gcc/gimple-fold.cc                            | 57 ++++++++++++++-----
>>  .../gcc.target/powerpc/p9-vec-length-epil-8.c |  2 +-
>>  gcc/testsuite/gcc.target/powerpc/pr107412.c   | 19 +++++++
>>  3 files changed, 64 insertions(+), 14 deletions(-)
>>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr107412.c
>>
>> diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
>> index a1704784bc9..e3a087defa6 100644
>> --- a/gcc/gimple-fold.cc
>> +++ b/gcc/gimple-fold.cc
>> @@ -5370,19 +5370,39 @@ arith_overflowed_p (enum tree_code code, const_tree type,
>>    return wi::min_precision (wres, sign) > TYPE_PRECISION (type);
>>  }
>>
>> -/* If IFN_MASK_LOAD/STORE call CALL is unconditional, return a MEM_REF
>> +/* If IFN_{MASK,LEN}_LOAD/STORE call CALL is unconditional, return a MEM_REF
>>     for the memory it references, otherwise return null.  VECTYPE is the
>> -   type of the memory vector.  */
>> +   type of the memory vector.  MASK_P indicates it's for MASK if true,
>> +   otherwise it's for LEN.  */
>>
>>  static tree
>> -gimple_fold_mask_load_store_mem_ref (gcall *call, tree vectype)
>> +gimple_fold_partial_load_store_mem_ref (gcall *call, tree vectype, bool mask_p)
>>  {
>>    tree ptr = gimple_call_arg (call, 0);
>>    tree alias_align = gimple_call_arg (call, 1);
>> -  tree mask = gimple_call_arg (call, 2);
>> -  if (!tree_fits_uhwi_p (alias_align) || !integer_all_onesp (mask))
>> +  if (!tree_fits_uhwi_p (alias_align))
>>      return NULL_TREE;
>>
>> +  if (mask_p)
>> +    {
>> +      tree mask = gimple_call_arg (call, 2);
>> +      if (!integer_all_onesp (mask))
>> +	return NULL_TREE;
>> +    } else {
> 
> Minor nit: }, else, and { should be on separate lines.  But the thing
> I actually wanted to say was...

Thanks for catching, I must have forgotten to reformat these lines.

> 
>> +      tree basic_len = gimple_call_arg (call, 2);
>> +      if (!tree_fits_uhwi_p (basic_len))
>> +	return NULL_TREE;
>> +      unsigned int nargs = gimple_call_num_args (call);
>> +      tree bias = gimple_call_arg (call, nargs - 1);
>> +      gcc_assert (tree_fits_uhwi_p (bias));
>> +      tree biased_len = int_const_binop (MINUS_EXPR, basic_len, bias);
>> +      unsigned int len = tree_to_uhwi (biased_len);
>> +      unsigned int vect_len
>> +	= GET_MODE_SIZE (TYPE_MODE (vectype)).to_constant ();
>> +      if (vect_len != len)
>> +	return NULL_TREE;
> 
> Using "unsigned int" truncates the value.  I realise that's probably
> safe in this context, since large values have undefined behaviour.
> But it still seems better to use an untruncated type, so that it
> looks less like an oversight.  (I think this is one case where "auto"
> can help, since it gets the type right automatically.)
> 
> It would also be better to avoid the to_constant, since we haven't
> proven is_constant.  How about:
> 
>       tree basic_len = gimple_call_arg (call, 2);
>       if (!poly_int_tree_p (basic_len))
> 	return NULL_TREE;
>       unsigned int nargs = gimple_call_num_args (call);
>       tree bias = gimple_call_arg (call, nargs - 1);
>       gcc_assert (TREE_CODE (bias) == INTEGER_CST);
>       if (maybe_ne (wi::to_poly_widest (basic_len) - wi::to_widest (bias),
> 		    GET_MODE_SIZE (TYPE_MODE (vectype))))
> 	return NULL_TREE;
> 
> which also avoids using tree arithmetic for the subtraction?

I agree your proposed code has better robustness, thanks!

Sorry that the original patch was committed, I made a patch as attached.
It's bootstrapped and regresss-tested on powerpc64-linux-gnu P8, and
powerpc64le-linux-gnu P9 and P10.

Is it ok for trunk?

BR,
Kewen


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From 3984a7f86a35d13e1fd40bc0c12ed5ad5b234047 Mon Sep 17 00:00:00 2001
From: Kewen Lin <linkw@linux.ibm.com>
Date: Sun, 27 Nov 2022 20:29:57 -0600
Subject: [PATCH] gimple-fold: Refine gimple_fold_partial_load_store_mem_ref

Following Richard's review comments, this patch is to use
untruncated type for the length used for IFN_LEN_{LOAD,STORE}
instead of "unsigned int" for better robustness.  It also
avoid to use to_constant and tree arithmetic for subtraction.

Co-authored-by: Richard Sandiford  <richard.sandiford@arm.com>

gcc/ChangeLog:

	* gimple-fold.cc (gimple_fold_partial_load_store_mem_ref): Use
	untruncated type for the length, and avoid to_constant and tree
	arithmetic for subtraction.
---
 gcc/gimple-fold.cc | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index c2d9c806aee..88d14c7adcc 100644
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -5387,18 +5387,17 @@ gimple_fold_partial_load_store_mem_ref (gcall *call, tree vectype, bool mask_p)
       tree mask = gimple_call_arg (call, 2);
       if (!integer_all_onesp (mask))
 	return NULL_TREE;
-    } else {
+    }
+  else
+    {
       tree basic_len = gimple_call_arg (call, 2);
-      if (!tree_fits_uhwi_p (basic_len))
+      if (!poly_int_tree_p (basic_len))
 	return NULL_TREE;
       unsigned int nargs = gimple_call_num_args (call);
       tree bias = gimple_call_arg (call, nargs - 1);
-      gcc_assert (tree_fits_shwi_p (bias));
-      tree biased_len = int_const_binop (MINUS_EXPR, basic_len, bias);
-      unsigned int len = tree_to_uhwi (biased_len);
-      unsigned int vect_len
-	= GET_MODE_SIZE (TYPE_MODE (vectype)).to_constant ();
-      if (vect_len != len)
+      gcc_assert (TREE_CODE (bias) == INTEGER_CST);
+      if (maybe_ne (wi::to_poly_widest (basic_len) - wi::to_widest (bias),
+		    GET_MODE_SIZE (TYPE_MODE (vectype))))
 	return NULL_TREE;
     }
 
-- 
2.27.0