[PATCH][vect] Don't set bogus bounds on epilogues [PR120805]

[Tamar Christina]

Hi All,

The testcases in the PR are failing due to the code trying to set a vector range
on an epilogue.

However on epilogues the range doesn't make sense.  In particular we are setting
ranged to help niters analysis. But the epilogue doesn't iterate.

Secondly the bounds variable hasn't been adjusted to vector iterations:

In the epilogue this is calculated as

  <bb 13> [local count: 81467476]:
  # i_127 = PHI <tmp.7_131(10), 0(5)>
  # _132 = PHI <_133(10), 0(5)>
  _181 = (unsigned int) n_41(D);
  bnd.31_180 = _181 - _132;

where

  _133 = niters_vector_mult_vf.6_130;

but _132 is a phi node, and if coming from the vector loop skip edge
_181 will be <1, VF>.

But this is a range VRP or Ranger can easily report due to the guard on the
skip_vector loop.

Previously, non-const VF would skip this code entirely due to the .is_constant()
check.

Non-partial vector loop would also skip it because the bounds would fold to a
constant. so it doesn't enter the !gimple_value check.

When support for partial vector ranges was added, this accidentally enabled
ranges on partial vector epilogues.

This patch now makes it explicit that ranges shouldn't be set for epilogues, as
they don't seem to be useful anyway.

Bootstrapped Regtested on aarch64-none-linux-gnu,
arm-none-linux-gnueabihf, x86_64-pc-linux-gnu
-m32, -m64 and no issues.

Also bootstrapped and Regtested powerpc64-unknown-linux-gnu
and failing tests now pass.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

        PR tree-optimization/120805
        * tree-vect-loop-manip.cc (vect_gen_vector_loop_niters): Skip setting
        bounds on epilogues.

---
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 
2d01a4b0ed1c8431510ad5e6e2175dbe89371618..c81aff76efa59a2424162b564010d44908f2b778
 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -2857,7 +2857,7 @@ vect_gen_vector_loop_niters (loop_vec_info loop_vinfo, 
tree niters,
         we set range information to make niters analyzer's life easier.
         Note the number of latch iteration value can be TYPE_MAX_VALUE so
         we have to represent the vector niter TYPE_MAX_VALUE + 1 / vf.  */
-      if (stmts != NULL && const_vf > 0)
+      if (stmts != NULL && const_vf > 0 && !LOOP_VINFO_EPILOGUE_P (loop_vinfo))
        {
          if (niters_no_overflow
              && LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo))


-- 

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 2d01a4b0ed1c8431510ad5e6e2175dbe89371618..c81aff76efa59a2424162b564010d44908f2b778 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -2857,7 +2857,7 @@ vect_gen_vector_loop_niters (loop_vec_info loop_vinfo, tree niters,
 	 we set range information to make niters analyzer's life easier.
 	 Note the number of latch iteration value can be TYPE_MAX_VALUE so
 	 we have to represent the vector niter TYPE_MAX_VALUE + 1 / vf.  */
-      if (stmts != NULL && const_vf > 0)
+      if (stmts != NULL && const_vf > 0 && !LOOP_VINFO_EPILOGUE_P (loop_vinfo))
 	{
 	  if (niters_no_overflow
 	      && LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo))