Drop overflow from constants while building ranges in ranger.

Sometimes the overflow flag will leak into the IL.  Drop it while
creating ranges.

There are various places we could plug this.  This patch just plugs things
at get_tree_range which is the entry point for ranges from tree expressions.
It fixes the PR, and probably fixes the ranger entirely, but we may need
to revisit this.

For example, I looked to see if there were other places that created
ranges with TREE_OVERFLOW set, and there are various.  For example,
the following code pattern appears multiple times in vr-values.c:

  else if (is_gimple_min_invariant (op0))
    vr0.set (op0);

This can pick up TREE_OVERFLOW from the IL if present.  However, the
ranger won't see them so we're good.

At some point we should audit all this.  Or perhaps just nuke all
TREE_OVERFLOW's at irange::set.

For now, this will do.

gcc/ChangeLog:

	PR tree-optimization/97721
	* gimple-range.cc (get_tree_range): Drop overflow from constants.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr97721.c: New test.

2 files changed, 15 insertions, 0 deletions

diff --git a/gcc/gimple-range.cc b/gcc/gimple-range.cc
index ef65e00..0c8ec40 100644
--- a/gcc/gimple-range.cc
+++ b/gcc/gimple-range.cc
@@ -165,6 +165,8 @@ get_tree_range (irange &r, tree expr)
   switch (TREE_CODE (expr))
     {
       case INTEGER_CST:
+	if (TREE_OVERFLOW_P (expr))
+	  expr = drop_tree_overflow (expr);
 	r.set (expr, expr);
 	return true;
 
diff --git a/gcc/testsuite/gcc.dg/pr97721.c b/gcc/testsuite/gcc.dg/pr97721.c
new file mode 100644
index 0000000..c2a2848
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr97721.c
@@ -0,0 +1,13 @@
+// { dg-do compile }
+// { dg-options "-O -fno-tree-dominator-opts" }
+
+int ot;
+
+void
+z6 (char *tw)
+{ 
+  while (ot >= 0)
+    --ot;
+
+  __builtin_strcpy (&tw[ot], tw);
+}