[PR,tree-optimization/64277] Improve loop iterations count estimation

On 27 Jan 12:29, Richard Biener wrote:
> On Tue, Jan 27, 2015 at 11:47 AM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
> > On 27 Jan 12:40, Ilya Enkovich wrote:
> >> Hi,
> >>
> >> This patch was supposed to fix PR tree-optimization/64277.  Tracker is now fixed by warnings disabling but I think patch is still useful to avoid dead code generated by complete unroll.
> >>
> >> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> >>
> >> Thanks,
> >> Ilya
> >> --
> >> gcc/
> >>
> >> 2015-01-27  Ilya Enkovich  <ilya.enkovich@intel.com>
> >>
> >>       * tree-ssa-loop-niter.c (record_nonwrapping_iv): Use base
> >>       range info when possible to refine estimation.
> >>
> >> gcc/testsuite/
> >>
> >> 2015-01-27  Ilya Enkovich  <ilya.enkovich@intel.com>
> >>
> >>       * gcc.dg/pr64277.c: New.
> >>
> >>
> >
> > Here is a new version fixed according to comments in the tracker.  I also fixed a test to scan cunroll dumps.  Does it look OK?
> 
> Minor comments below.
> 
> > What are possible branches for this patch?
> 
> You can probably create a testcase that shows code-size regressions
> against a version that didn't peel completely (GCC 4.7).  Thus I'd say
> it would apply to 4.9 as well (4.8 doesn't have range information).
> 
> > Thanks,
> > Ilya
> > --
> > diff --git a/gcc/testsuite/gcc.dg/pr64277.c b/gcc/testsuite/gcc.dg/pr64277.c
> > new file mode 100644
> > index 0000000..c6ef331
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/pr64277.c
> > @@ -0,0 +1,23 @@
> > +/* PR tree-optimization/64277 */
> > +/* { dg-do compile } */
> > +/* { dg-options "-O3 -Wall -Werror -fdump-tree-cunroll-details" } */
> > +/* { dg-final { scan-tree-dump "loop with 5 iterations completely unrolled" "cunroll" } } */
> > +/* { dg-final { scan-tree-dump "loop with 6 iterations completely unrolled" "cunroll" } } */
> > +/* { dg-final { cleanup-tree-dump "cunroll" } } */
> > +
> > +int f1[10];
> > +void test1 (short a[], short m, unsigned short l)
> > +{
> > +  int i = l;
> > +  for (i = i + 5; i < m; i++)
> > +    f1[i] = a[i]++;
> > +}
> > +
> > +void test2 (short a[], short m, short l)
> > +{
> > +  int i;
> > +  if (m > 5)
> > +    m = 5;
> > +  for (i = m; i > l; i--)
> > +    f1[i] = a[i]++;
> > +}
> > diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
> > index 919f5c0..1cd297d 100644
> > --- a/gcc/tree-ssa-loop-niter.c
> > +++ b/gcc/tree-ssa-loop-niter.c
> > @@ -2754,6 +2754,7 @@ record_nonwrapping_iv (struct loop *loop, tree base, tree step, gimple stmt,
> >  {
> >    tree niter_bound, extreme, delta;
> >    tree type = TREE_TYPE (base), unsigned_type;
> > +  tree orig_base = base;
> >
> >    if (TREE_CODE (step) != INTEGER_CST || integer_zerop (step))
> >      return;
> > @@ -2777,16 +2778,30 @@ record_nonwrapping_iv (struct loop *loop, tree base, tree step, gimple stmt,
> >
> >    if (tree_int_cst_sign_bit (step))
> >      {
> > +      wide_int min, max;
> >        extreme = fold_convert (unsigned_type, low);
> > -      if (TREE_CODE (base) != INTEGER_CST)
> > +      if (TREE_CODE (orig_base) == SSA_NAME
> > +         && TREE_CODE (high) == INTEGER_CST
> > +         && INTEGRAL_TYPE_P (TREE_TYPE (orig_base))
> > +         && get_range_info (orig_base, &min, &max) == VR_RANGE
> > +         && wi::gts_p (wide_int (high), max))
> 
> For me a simple wi::gts_p (high, max) worked fine.
> 
> > +       base = wide_int_to_tree (unsigned_type, max);
> > +      else if (TREE_CODE (base) != INTEGER_CST)
> >         base = fold_convert (unsigned_type, high);
> >        delta = fold_build2 (MINUS_EXPR, unsigned_type, base, extreme);
> >        step = fold_build1 (NEGATE_EXPR, unsigned_type, step);
> >      }
> >    else
> >      {
> > +      wide_int min, max;
> >        extreme = fold_convert (unsigned_type, high);
> > -      if (TREE_CODE (base) != INTEGER_CST)
> > +      if (TREE_CODE (orig_base) == SSA_NAME
> > +         && TREE_CODE (low) == INTEGER_CST
> > +         && INTEGRAL_TYPE_P (TREE_TYPE (orig_base))
> > +         && get_range_info (orig_base, &min, &max) == VR_RANGE
> > +         && wi::gts_p (min, wide_int (low)))
> 
> Likewise.
> 
> Ok for trunk with that changes.  For the 4.9 branch you need to adjust
> the patch to not use wide-ints.  I'd leave it on trunk for a while and
> eventually open a bugreport for the size regression to keep track of it.
> 
> Thanks,
> Richard.
> 

Thanks a lot for review!  Here is a final version for GCC 5.0.  Will prepare 4.9 version later.

Thanks,
Ilya
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