Do not calculate new values when evaluating a debug statement.

Add a flag to enable/disable immediately improving poor values found during
cache propagation. Then disable it when processing debug statements.

	gcc/
	PR tree-optimization/100781
	* gimple-range-cache.cc (ranger_cache::ranger_cache): Enable new
	value calculation by default.
	(ranger_cache::enable_new_values): New.
	(ranger_cache::disable_new_values): New.
	(ranger_cache::push_poor_value): Check if new values are allowed.
	* gimple-range-cache.h (class ranger_cache): New member/methods.
	* gimple-range.cc (gimple_ranger::range_of_expr): Check for debug
	statement, and disable/renable new value calculation.

	gcc/testsuite/
	PR tree-optimization/100781
	* gcc.dg/pr100781.c: New.

1 files changed, 9 insertions, 0 deletions

diff --git a/gcc/gimple-range.cc b/gcc/gimple-range.cc
index d58e151..ed0a0c9 100644
--- a/gcc/gimple-range.cc
+++ b/gcc/gimple-range.cc
@@ -971,6 +971,15 @@ gimple_ranger::range_of_expr (irange &r, tree expr, gimple *stmt)
       return true;
     }
 
+  // For a debug stmt, pick the best value currently available, do not
+  // trigger new value calculations.  PR 100781.
+  if (is_gimple_debug (stmt))
+    {
+      m_cache.disable_new_values ();
+      m_cache.range_of_expr (r, expr, stmt);
+      m_cache.enable_new_values ();
+      return true;
+    }
   basic_block bb = gimple_bb (stmt);
   gimple *def_stmt = SSA_NAME_DEF_STMT (expr);