[RFA,PATCH] Bail in bounds_of_var_in_loop if no step found.

[Aldy Hernandez]

[Neither Andrew nor I are familiar with the SCEV code.  We treat it as a
black box :).  So we could use a SCEV expert here.]

In bounds_of_var_in_loop, evolution_part_in_loop_num is returning NULL:

   step = evolution_part_in_loop_num (chrec, loop->num);

and we ICE while trying to calculate the range for STEP.

This is for:

(gdb) dd stmt
qx.0_3 = PHI <qx.0_1(3)>
(gdb) dd var
qx.0_3

It looks like NULL is a perfectly valid response from
evolution_part_in_loop_num.  Should we just bail if NULL?

If bailing is the correct solution, the following patch fixes the PR and
passes tests.

Thanks.
Aldy

gcc/ChangeLog:

	PR tree-optimization/97396
	* vr-values.c (bounds_of_var_in_loop): Bail on no step.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr97396.c: New test.
---
 gcc/testsuite/gcc.dg/pr97396.c | 23 +++++++++++++++++++++++
 gcc/vr-values.c                |  2 ++
 2 files changed, 25 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr97396.c

diff --git a/gcc/testsuite/gcc.dg/pr97396.c b/gcc/testsuite/gcc.dg/pr97396.c
new file mode 100644
index 00000000000..d992c11f238
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr97396.c
@@ -0,0 +1,23 @@
+// { dg-do compile }
+// { dg-options "-O1 -ftree-vrp" }
+// { dg-additional-options "-m32" { target { i?86-*-* x86_64-*-* } } }
+
+unsigned int
+po (char *os, unsigned int al)
+{
+  for (;;)
+    {
+      int qx = 0;
+
+      while (al < 1)
+        {
+          char *cw;
+
+          cw = os + qx;
+          if (cw)
+            return al + qx;
+
+          qx += sizeof *cw;
+        }
+    }
+}
diff --git a/gcc/vr-values.c b/gcc/vr-values.c
index da0b249278b..16f6c629f29 100644
--- a/gcc/vr-values.c
+++ b/gcc/vr-values.c
@@ -1827,6 +1827,8 @@ bounds_of_var_in_loop (tree *min, tree *max, range_query *query,
 
   init = initial_condition_in_loop_num (chrec, loop->num);
   step = evolution_part_in_loop_num (chrec, loop->num);
+  if (step == NULL_TREE)
+    return false;
 
   /* If INIT is an SSA with a singleton range, set INIT to said
      singleton, otherwise leave INIT alone.  */
-- 
2.25.4