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.

8 files changed, 73 insertions, 9 deletions

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-16.c b/gcc/testsuite/gcc.dg/tree-ssa/scev-16.c
new file mode 100644
index 0000000..120f40c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-16.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-details" } */
+
+int A[1024 * 2];
+
+int foo (unsigned offset, unsigned N)
+{
+  int sum = 0;
+
+  for (unsigned i = 0; i < N; i++)
+    sum += A[i + offset];
+
+  return sum;
+}
+
+/* Loop can be vectorized by referring "i + offset" is nonwrapping from array.  */
+/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" { target { ! { avr-*-* msp430-*-* pru-*-* } } } } } */
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 65e51b9..04c04cf 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1387,6 +1387,9 @@ struct GTY(()) tree_base {
        DECL_NONALIASED in
 	  VAR_DECL
 
+       CHREC_NOWRAP in
+	  POLYNOMIAL_CHREC
+
    deprecated_flag:
 
        TREE_DEPRECATED in
diff --git a/gcc/tree-pretty-print.cc b/gcc/tree-pretty-print.cc
index 1fadd75..0dabb6d 100644
--- a/gcc/tree-pretty-print.cc
+++ b/gcc/tree-pretty-print.cc
@@ -3488,7 +3488,7 @@ dump_generic_node (pretty_printer *pp, tree node, int spc, dump_flags_t flags,
       dump_generic_node (pp, CHREC_LEFT (node), spc, flags, false);
       pp_string (pp, ", +, ");
       dump_generic_node (pp, CHREC_RIGHT (node), spc, flags, false);
-      pp_string (pp, "}_");
+      pp_string (pp, !CHREC_NOWRAP (node) ? "}_" : "}<nw>_");
       pp_scalar (pp, "%u", CHREC_VARIABLE (node));
       is_stmt = false;
       break;
diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 385fc64..94250b1 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -2050,6 +2050,30 @@ analyze_scalar_evolution (class loop *loop, tree var)
   return res;
 }
 
+/* If CHREC doesn't overflow, set the nonwrapping flag.  */
+
+void record_nonwrapping_chrec (tree chrec)
+{
+  CHREC_NOWRAP(chrec) = 1;
+
+  if (dump_file && (dump_flags & TDF_SCEV))
+    {
+      fprintf (dump_file, "(record_nonwrapping_chrec: ");
+      print_generic_expr (dump_file, chrec);
+      fprintf (dump_file, ")\n");
+    }
+}
+
+/* Return true if CHREC's nonwrapping flag is set.  */
+
+bool nonwrapping_chrec_p (tree chrec)
+{
+  if (!chrec || TREE_CODE(chrec) != POLYNOMIAL_CHREC)
+    return false;
+
+  return CHREC_NOWRAP(chrec);
+}
+
 /* Analyzes and returns the scalar evolution of VAR address in LOOP.  */
 
 static tree
diff --git a/gcc/tree-scalar-evolution.h b/gcc/tree-scalar-evolution.h
index a64ed78..f57fde1 100644
--- a/gcc/tree-scalar-evolution.h
+++ b/gcc/tree-scalar-evolution.h
@@ -43,6 +43,8 @@ extern bool simple_iv (class loop *, class loop *, tree, struct affine_iv *,
 		       bool);
 extern bool iv_can_overflow_p (class loop *, tree, tree, tree);
 extern tree compute_overall_effect_of_inner_loop (class loop *, tree);
+extern void record_nonwrapping_chrec (tree);
+extern bool nonwrapping_chrec_p (tree);
 
 /* Returns the basic block preceding LOOP, or the CFG entry block when
    the loop is function's body.  */
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;
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index dd584ab..6261cd1 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -3570,6 +3570,10 @@ vect_analyze_loop (class loop *loop, vec_info_shared *shared)
 	 analysis are done under the assumptions.  */
       loop_constraint_set (loop, LOOP_C_FINITE);
     }
+  else
+    /* Clear the existing niter information to make sure the nonwrapping flag
+       will be calculated and set propriately.  */
+    free_numbers_of_iterations_estimates (loop);
 
   auto_vector_modes vector_modes;
   /* Autodetect first vector size we try.  */
diff --git a/gcc/tree.h b/gcc/tree.h
index 086b55f..59af892 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1438,9 +1438,11 @@ class auto_suppress_location_wrappers
 #define COND_EXPR_ELSE(NODE)	(TREE_OPERAND (COND_EXPR_CHECK (NODE), 2))
 
 /* Accessors for the chains of recurrences.  */
-#define CHREC_LEFT(NODE)          TREE_OPERAND (POLYNOMIAL_CHREC_CHECK (NODE), 0)
-#define CHREC_RIGHT(NODE)         TREE_OPERAND (POLYNOMIAL_CHREC_CHECK (NODE), 1)
-#define CHREC_VARIABLE(NODE)      POLYNOMIAL_CHREC_CHECK (NODE)->base.u.chrec_var
+#define CHREC_LEFT(NODE)        TREE_OPERAND (POLYNOMIAL_CHREC_CHECK (NODE), 0)
+#define CHREC_RIGHT(NODE)       TREE_OPERAND (POLYNOMIAL_CHREC_CHECK (NODE), 1)
+#define CHREC_VARIABLE(NODE)    POLYNOMIAL_CHREC_CHECK (NODE)->base.u.chrec_var
+/* Nonzero if this chrec doesn't overflow (i.e., nonwrapping).  */
+#define CHREC_NOWRAP(NODE)      POLYNOMIAL_CHREC_CHECK (NODE)->base.nothrow_flag
 
 /* LABEL_EXPR accessor. This gives access to the label associated with
    the given label expression.  */