Re: [PATCH] Fix PR60505

[Cong Hou <congh at google dot com>]

Ping?


thanks,
Cong


On Wed, Mar 19, 2014 at 11:39 AM, Cong Hou <congh@google.com> wrote:
> On Tue, Mar 18, 2014 at 4:43 AM, Richard Biener <rguenther@suse.de> wrote:
>>
>> On Mon, 17 Mar 2014, Cong Hou wrote:
>>
>> > On Mon, Mar 17, 2014 at 6:44 AM, Richard Biener <rguenther@suse.de> wrote:
>> > > On Fri, 14 Mar 2014, Cong Hou wrote:
>> > >
>> > >> On Fri, Mar 14, 2014 at 12:58 AM, Richard Biener <rguenther@suse.de> wrote:
>> > >> > On Fri, 14 Mar 2014, Jakub Jelinek wrote:
>> > >> >
>> > >> >> On Fri, Mar 14, 2014 at 08:52:07AM +0100, Richard Biener wrote:
>> > >> >> > > Consider this fact and if there are alias checks, we can safely remove
>> > >> >> > > the epilogue if the maximum trip count of the loop is less than or
>> > >> >> > > equal to the calculated threshold.
>> > >> >> >
>> > >> >> > You have to consider n % vf != 0, so an argument on only maximum
>> > >> >> > trip count or threshold cannot work.
>> > >> >>
>> > >> >> Well, if you only check if maximum trip count is <= vf and you know
>> > >> >> that for n < vf the vectorized loop + it's epilogue path will not be taken,
>> > >> >> then perhaps you could, but it is a very special case.
>> > >> >> Now, the question is when we are guaranteed we enter the scalar versioned
>> > >> >> loop instead for n < vf, is that in case of versioning for alias or
>> > >> >> versioning for alignment?
>> > >> >
>> > >> > I think neither - I have plans to do the cost model check together
>> > >> > with the versioning condition but didn't get around to implement that.
>> > >> > That would allow stronger max bounds for the epilogue loop.
>> > >>
>> > >> In vect_transform_loop(), check_profitability will be set to true if
>> > >> th >= VF-1 and the number of iteration is unknown (we only consider
>> > >> unknown trip count here), where th is calculated based on the
>> > >> parameter PARAM_MIN_VECT_LOOP_BOUND and cost model, with the minimum
>> > >> value VF-1. If the loop needs to be versioned, then
>> > >> check_profitability with true value will be passed to
>> > >> vect_loop_versioning(), in which an enhanced loop bound check
>> > >> (considering cost) will be built. So I think if the loop is versioned
>> > >> and n < VF, then we must enter the scalar version, and in this case
>> > >> removing epilogue should be safe when the maximum trip count <= th+1.
>> > >
>> > > You mean exactly in the case where the profitability check ensures
>> > > that n % vf == 0?  Thus effectively if n == maximum trip count?
>> > > That's quite a special case, no?
>> >
>> >
>> > Yes, it is a special case. But it is in this special case that those
>> > warnings are thrown out. Also, I think declaring an array with VF*N as
>> > length is not unusual.
>>
>> Ok, but then for the patch compute the cost model threshold once
>> in vect_analyze_loop_2 and store it in a new
>> LOOP_VINFO_COST_MODEL_THRESHOLD.
>
>
> Done.
>
>
>> Also you have to check
>> the return value from max_stmt_executions_int as that may return
>> -1 if the number cannot be computed (or isn't representable in
>> a HOST_WIDE_INT).
>
>
> It will be converted to unsigned type so that -1 means infinity.
>
>
>> You also should check for
>> LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT which should have the
>> same effect on the cost model check.
>
>
> Done.
>
>
>>
>>
>> The existing condition is already complicated enough - adding new
>> stuff warrants comments before the (sub-)checks.
>
>
> OK. Comments added.
>
> Below is the revised patch. Bootstrapped and tested on a x86-64 machine.
>
>
> Cong
>
>
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index e1d8666..eceefb3 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,18 @@
> +2014-03-11  Cong Hou  <congh@google.com>
> +
> + PR tree-optimization/60505
> + * tree-vectorizer.h (struct _stmt_vec_info): Add th field as the
> + threshold of number of iterations below which no vectorization will be
> + done.
> + * tree-vect-loop.c (new_loop_vec_info):
> + Initialize LOOP_VINFO_COST_MODEL_THRESHOLD.
> + * tree-vect-loop.c (vect_analyze_loop_operations):
> + Set LOOP_VINFO_COST_MODEL_THRESHOLD.
> + * tree-vect-loop.c (vect_transform_loop):
> + Use LOOP_VINFO_COST_MODEL_THRESHOLD.
> + * tree-vect-loop.c (vect_analyze_loop_2): Check the maximum number
> + of iterations of the loop and see if we should build the epilogue.
> +
>  2014-03-10  Jakub Jelinek  <jakub@redhat.com>
>
>   PR ipa/60457
> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
> index 41b6875..09ec1c0 100644
> --- a/gcc/testsuite/ChangeLog
> +++ b/gcc/testsuite/ChangeLog
> @@ -1,3 +1,8 @@
> +2014-03-11  Cong Hou  <congh@google.com>
> +
> + PR tree-optimization/60505
> + * gcc.dg/vect/pr60505.c: New test.
> +
>  2014-03-10  Jakub Jelinek  <jakub@redhat.com>
>
>   PR ipa/60457
> diff --git a/gcc/testsuite/gcc.dg/vect/pr60505.c
> b/gcc/testsuite/gcc.dg/vect/pr60505.c
> new file mode 100644
> index 0000000..6940513
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr60505.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-Wall -Werror" } */
> +
> +void foo(char *in, char *out, int num)
> +{
> +  int i;
> +  char ovec[16] = {0};
> +
> +  for(i = 0; i < num ; ++i)
> +    out[i] = (ovec[i] = in[i]);
> +  out[num] = ovec[num/2];
> +}
> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
> index df6ab6f..1c78e11 100644
> --- a/gcc/tree-vect-loop.c
> +++ b/gcc/tree-vect-loop.c
> @@ -933,6 +933,7 @@ new_loop_vec_info (struct loop *loop)
>    LOOP_VINFO_NITERS (res) = NULL;
>    LOOP_VINFO_NITERS_UNCHANGED (res) = NULL;
>    LOOP_VINFO_COST_MODEL_MIN_ITERS (res) = 0;
> +  LOOP_VINFO_COST_MODEL_THRESHOLD (res) = 0;
>    LOOP_VINFO_VECTORIZABLE_P (res) = 0;
>    LOOP_VINFO_PEELING_FOR_ALIGNMENT (res) = 0;
>    LOOP_VINFO_VECT_FACTOR (res) = 0;
> @@ -1579,6 +1580,8 @@ vect_analyze_loop_operations (loop_vec_info
> loop_vinfo, bool slp)
>            || min_profitable_iters > min_scalar_loop_bound))
>      th = (unsigned) min_profitable_iters;
>
> +  LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo) = th;
> +
>    if (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
>        && LOOP_VINFO_INT_NITERS (loop_vinfo) <= th)
>      {
> @@ -1625,6 +1628,7 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo)
>    bool ok, slp = false;
>    int max_vf = MAX_VECTORIZATION_FACTOR;
>    int min_vf = 2;
> +  unsigned int th;
>
>    /* Find all data references in the loop (which correspond to vdefs/vuses)
>       and analyze their evolution in the loop.  Also adjust the minimal
> @@ -1769,6 +1773,10 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo)
>
>    /* Decide whether we need to create an epilogue loop to handle
>       remaining scalar iterations.  */
> +  th = ((LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo) + 1)
> +        / LOOP_VINFO_VECT_FACTOR (loop_vinfo))
> +       * LOOP_VINFO_VECT_FACTOR (loop_vinfo);
> +
>    if (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
>        && LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo) > 0)
>      {
> @@ -1779,7 +1787,14 @@ vect_analyze_loop_2 (loop_vec_info loop_vinfo)
>      }
>    else if (LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo)
>     || (tree_ctz (LOOP_VINFO_NITERS (loop_vinfo))
> -       < (unsigned)exact_log2 (LOOP_VINFO_VECT_FACTOR (loop_vinfo))))
> +       < (unsigned)exact_log2 (LOOP_VINFO_VECT_FACTOR (loop_vinfo))
> +               /* In case of versioning, check if the maximum number of
> +                  iterations is greater than th.  If they are identical,
> +                  the epilogue is unnecessary.  */
> +       && ((!LOOP_REQUIRES_VERSIONING_FOR_ALIAS (loop_vinfo)
> +            && !LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT (loop_vinfo))
> +                   || (unsigned HOST_WIDE_INT)max_stmt_executions_int
> +        (LOOP_VINFO_LOOP (loop_vinfo)) > th)))
>      LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo) = true;
>
>    /* If an epilogue loop is required make sure we can create one.  */
> @@ -5775,9 +5790,7 @@ vect_transform_loop (loop_vec_info loop_vinfo)
>       by our caller.  If the threshold makes all loops profitable that
>       run at least the vectorization factor number of times checking
>       is pointless, too.  */
> -  th = ((PARAM_VALUE (PARAM_MIN_VECT_LOOP_BOUND)
> - * LOOP_VINFO_VECT_FACTOR (loop_vinfo)) - 1);
> -  th = MAX (th, LOOP_VINFO_COST_MODEL_MIN_ITERS (loop_vinfo));
> +  th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo);
>    if (th >= LOOP_VINFO_VECT_FACTOR (loop_vinfo) - 1
>        && !LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo))
>      {
> diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
> index f8efe47..f2087e2 100644
> --- a/gcc/tree-vectorizer.h
> +++ b/gcc/tree-vectorizer.h
> @@ -264,6 +264,11 @@ typedef struct _loop_vec_info {
>       values unknown at compile time.  */
>    int min_profitable_iters;
>
> +  /* Threshold of number of iterations below which vectorzation will not be
> +     performed. It is calculated from MIN_PROFITABLE_ITERS and
> +     PARAM_MIN_VECT_LOOP_BOUND.  */
> +  unsigned int th;
> +
>    /* Is the loop vectorizable? */
>    bool vectorizable;
>
> @@ -382,6 +387,7 @@ typedef struct _loop_vec_info {
>     cost model.  */
>  #define LOOP_VINFO_NITERS_UNCHANGED(L)     (L)->num_iters_unchanged
>  #define LOOP_VINFO_COST_MODEL_MIN_ITERS(L) (L)->min_profitable_iters
> +#define LOOP_VINFO_COST_MODEL_THRESHOLD(L) (L)->th
>  #define LOOP_VINFO_VECTORIZABLE_P(L)       (L)->vectorizable
>  #define LOOP_VINFO_VECT_FACTOR(L)          (L)->vectorization_factor
>  #define LOOP_VINFO_PTR_MASK(L)             (L)->ptr_mask
>
>
>
>
>
>>
>>
>> Richard.