tree-optimization/112774: extend the SCEV CHREC tree with a nonwrapping flag

The flag is defined as CHREC_NOWRAP(tree), and will be dumped from
"{offset, +, 1}_1" to "{offset, +, 1}<nw>_1" (nw is short for nonwrapping).
Two SCEV interfaces record_nonwrapping_chrec and nonwrapping_chrec_p are
added to set and check the flag respectively.

As resetting the SCEV cache (i.e., the chrec trees) may not reset the
loop->estimate_state, free_numbers_of_iterations_estimates is called
explicitly in loop vectorization to make sure the flag can be
calculated propriately by niter.

gcc/ChangeLog:

	PR tree-optimization/112774
	* tree-pretty-print.cc: if nonwrapping flag is set, chrec will be
	printed with additional <nw> info.
	* tree-scalar-evolution.cc: add record_nonwrapping_chrec and
	nonwrapping_chrec_p to set and check the new flag respectively.
	* tree-scalar-evolution.h: Likewise.
	* tree-ssa-loop-niter.cc (idx_infer_loop_bounds,
	infer_loop_bounds_from_pointer_arith, infer_loop_bounds_from_signedness,
	scev_probably_wraps_p): call record_nonwrapping_chrec before
	record_nonwrapping_iv, call nonwrapping_chrec_p to check the flag is
	set and	return false from scev_probably_wraps_p.
	* tree-vect-loop.cc (vect_analyze_loop): call
	free_numbers_of_iterations_estimates explicitly.
	* tree-core.h: document the nothrow_flag usage in CHREC_NOWRAP
	* tree.h: add CHREC_NOWRAP(NODE), base.nothrow_flag is used to
	represent the nonwrapping info.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/scev-16.c: New test.

1 files changed, 16 insertions, 5 deletions

diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 2098bef..d465e0e 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -4206,11 +4206,15 @@ idx_infer_loop_bounds (tree base, tree *idx, void *dta)
 
   /* If access is not executed on every iteration, we must ensure that overlow
      may not make the access valid later.  */
-  if (!dominated_by_p (CDI_DOMINATORS, loop->latch, gimple_bb (data->stmt))
-      && scev_probably_wraps_p (NULL_TREE,
-				initial_condition_in_loop_num (ev, loop->num),
-				step, data->stmt, loop, true))
-    upper = false;
+  if (!dominated_by_p (CDI_DOMINATORS, loop->latch, gimple_bb (data->stmt)))
+    {
+      if (scev_probably_wraps_p (NULL_TREE,
+				 initial_condition_in_loop_num (ev, loop->num),
+				 step, data->stmt, loop, true))
+	upper = false;
+    }
+  else
+    record_nonwrapping_chrec (ev);
 
   record_nonwrapping_iv (loop, init, step, data->stmt, low, high, false, upper);
   return true;
@@ -4324,6 +4328,7 @@ infer_loop_bounds_from_pointer_arith (class loop *loop, gimple *stmt)
   if (flag_delete_null_pointer_checks && int_cst_value (low) == 0)
     low = build_int_cstu (TREE_TYPE (low), TYPE_ALIGN_UNIT (TREE_TYPE (type)));
 
+  record_nonwrapping_chrec (scev);
   record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true);
 }
 
@@ -4371,6 +4376,7 @@ infer_loop_bounds_from_signedness (class loop *loop, gimple *stmt)
       high = wide_int_to_tree (type, r.upper_bound ());
     }
 
+  record_nonwrapping_chrec (scev);
   record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true);
 }
 
@@ -5505,6 +5511,11 @@ scev_probably_wraps_p (tree var, tree base, tree step,
   if (loop_exits_before_overflow (base, step, at_stmt, loop))
     return false;
 
+  /* Check the nonwrapping flag, which may be set by niter analysis (e.g., the
+     above loop exits before overflow).  */
+  if (var && nonwrapping_chrec_p (analyze_scalar_evolution (loop, var)))
+    return false;
+
   /* At this point we still don't have a proof that the iv does not
      overflow: give up.  */
   return true;