Re: [PATCH] Set bound/cmp/control for until wrap loop.

[guojiufu <guojiufu@linux.ibm.com>]

On 2021-08-30 20:02, Richard Biener wrote:
> On Mon, 30 Aug 2021, guojiufu wrote:
> 
>> On 2021-08-30 14:15, Jiufu Guo wrote:
>> > Hi,
>> >
>> > In patch r12-3136, niter->control, niter->bound and niter->cmp are
>> > derived from number_of_iterations_lt.  While for 'until wrap condition',
>> > the calculation in number_of_iterations_lt is not align the requirements
>> > on the define of them and requirements in determine_exit_conditions.
>> >
>> > This patch calculate niter->control, niter->bound and niter->cmp in
>> > number_of_iterations_until_wrap.
>> >
>> > The ICEs in the PR are pass with this patch.
>> > Bootstrap and reg-tests pass on ppc64/ppc64le and x86.
>> > Is this ok for trunk?
>> >
>> > BR.
>> > Jiufu Guo
>> >
>> Add ChangeLog:
>> gcc/ChangeLog:
>> 
>> 2021-08-30  Jiufu Guo  <guojiufu@linux.ibm.com>
>> 
>>         PR tree-optimization/102087
>>         * tree-ssa-loop-niter.c (number_of_iterations_until_wrap):
>>         Set bound/cmp/control for niter.
>> 
>> gcc/testsuite/ChangeLog:
>> 
>> 2021-08-30  Jiufu Guo  <guojiufu@linux.ibm.com>
>> 
>>         PR tree-optimization/102087
>>         * gcc.dg/vect/pr101145_3.c: Update tests.
>>         * gcc.dg/pr102087.c: New test.
>> 
>> > ---
>> >  gcc/tree-ssa-loop-niter.c              | 14 +++++++++++++-
>> >  gcc/testsuite/gcc.dg/pr102087.c        | 25 +++++++++++++++++++++++++
>> >  gcc/testsuite/gcc.dg/vect/pr101145_3.c |  4 +++-
>> >  3 files changed, 41 insertions(+), 2 deletions(-)
>> >  create mode 100644 gcc/testsuite/gcc.dg/pr102087.c
>> >
>> > diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
>> > index 7af92d1c893..747f04d3ce0 100644
>> > --- a/gcc/tree-ssa-loop-niter.c
>> > +++ b/gcc/tree-ssa-loop-niter.c
>> > @@ -1482,7 +1482,7 @@ number_of_iterations_until_wrap (class loop *,
>> > tree type, affine_iv *iv0,
>> >  				 affine_iv *iv1, class tree_niter_desc *niter)
>> >  {
>> >    tree niter_type = unsigned_type_for (type);
>> > -  tree step, num, assumptions, may_be_zero;
>> > +  tree step, num, assumptions, may_be_zero, span;
>> >    wide_int high, low, max, min;
>> >
>> >    may_be_zero = fold_build2 (LE_EXPR, boolean_type_node, iv1->base,
>> > iv0->base);
>> > @@ -1513,6 +1513,8 @@ number_of_iterations_until_wrap (class loop *,
>> > tree type, affine_iv *iv0,
>> >   low = wi::to_wide (iv0->base);
>> >         else
>> > 	low = min;
>> > +
>> > +      niter->control = *iv1;
>> >      }
>> >    /* {base, -C} < n.  */
>> >    else if (tree_int_cst_sign_bit (iv0->step) && integer_zerop
>> > (iv1->step))
>> > @@ -1533,6 +1535,8 @@ number_of_iterations_until_wrap (class loop *,
>> > tree type, affine_iv *iv0,
>> >   high = wi::to_wide (iv1->base);
>> >         else
>> > 	high = max;
>> > +
>> > +      niter->control = *iv0;
>> >      }
>> >    else
>> >      return false;
> 
> it looks like the above two should already be in effect from the
> caller (guarding with integer_nozerop)?

I add them just because set these fields in one function.
Yes, they have been set in caller already,  I could remove them here.

> 
>> > @@ -1556,6 +1560,14 @@ number_of_iterations_until_wrap (class loop *,
>> > tree type, affine_iv *iv0,
>> >            niter->assumptions, assumptions);
>> >
>> >    niter->control.no_overflow = false;
>> > +  niter->control.base = fold_build2 (MINUS_EXPR, niter_type,
>> > +				     niter->control.base,
>> > niter->control.step);
> 
> how do we know IVn - STEP doesn't already wrap?

The last IV value is just cross the max/min value of the type
at the last iteration,  then IVn - STEP is the nearest value
to max(or min) and not wrap.

> A comment might be
> good to explain you're turning the simplified exit condition into
> 
>    { IVbase - STEP, +, STEP } != niter * STEP + (IVbase - STEP)
> 
> which, when mathematically looking at it makes me wonder why there's
> the seemingly redundant '- STEP' term?  Also is NE_EXPR really
> correct since STEP might be not 1?  Only for non equality compares
> the '- STEP' should matter?

I need to add comments for this.  This is a little tricky.
The last value of the original IV just cross max/min at most one STEP,
at there wrapping already happen.
Using "{IVbase, +, STEP} != niter * STEP + IVbase" is not wrong
in the aspect of exit condition.

But this would not work well with existing code:
like determine_exit_conditions, which will convert NE_EXP to
LT_EXPR/GT_EXPR.  And so, the '- STEP' is added to adjust the
IV.base and bound, with '- STEP' the bound will be the last value
just before wrap.

Thanks again for your review!

BR.
Jiufu

> 
> Richard.
> 
>> > +  span = fold_build2 (MULT_EXPR, niter_type, niter->niter,
>> > +		      fold_convert (niter_type, niter->control.step));
>> > +  niter->bound = fold_build2 (PLUS_EXPR, niter_type, span,
>> > +			      fold_convert (niter_type, niter->control.base));
>> > +  niter->bound = fold_convert (type, niter->bound);
>> > +  niter->cmp = NE_EXPR;
>> >
>> >    return true;
>> > }
>> > diff --git a/gcc/testsuite/gcc.dg/pr102087.c
>> > b/gcc/testsuite/gcc.dg/pr102087.c
>> > new file mode 100644
>> > index 00000000000..ef1f9f5cba9
>> > --- /dev/null
>> > +++ b/gcc/testsuite/gcc.dg/pr102087.c
>> > @@ -0,0 +1,25 @@
>> > +/* { dg-do compile } */
>> > +/* { dg-options "-O3" } */
>> > +
>> > +unsigned __attribute__ ((noinline))
>> > +foo (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
>> > +{
>> > +  while (n < ++l)
>> > +    *a++ = *b++ + 1;
>> > +  return l;
>> > +}
>> > +
>> > +volatile int a[1];
>> > +unsigned b;
>> > +int c;
>> > +
>> > +int
>> > +check ()
>> > +{
>> > +  int d;
>> > +  for (; b > 1; b++)
>> > +    for (c = 0; c < 2; c++)
>> > +      for (d = 0; d < 2; d++)
>> > +	a[0];
>> > +  return 0;
>> > +}
>> > diff --git a/gcc/testsuite/gcc.dg/vect/pr101145_3.c
>> > b/gcc/testsuite/gcc.dg/vect/pr101145_3.c
>> > index 99289afec0b..40cb0240aaa 100644
>> > --- a/gcc/testsuite/gcc.dg/vect/pr101145_3.c
>> > +++ b/gcc/testsuite/gcc.dg/vect/pr101145_3.c
>> > @@ -1,5 +1,6 @@
>> >  /* { dg-require-effective-target vect_int } */
>> >  /* { dg-options "-O3 -fdump-tree-vect-details" } */
>> > +
>> >  #define TYPE int *
>> >  #define MIN ((TYPE)0)
>> >  #define MAX ((TYPE)((long long)-1))
>> > @@ -10,4 +11,5 @@
>> >
>> >  #include "pr101145.inc"
>> >
>> > -/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" } } */
>> > +/* pointer size may not be vectorized, checking niter is ok. */
>> > +/* { dg-final { scan-tree-dump "Symbolic number of iterations is" "vect" }
>> > } */
>>