[gcc r12-9091] Correctly detect shifts out of range

[Andrew Macleod <amacleod@gcc.gnu.org>]

https://gcc.gnu.org/g:9dccaeaa586a1634e1f6a0f4c51806f3c3aea63b

commit r12-9091-g9dccaeaa586a1634e1f6a0f4c51806f3c3aea63b
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Mon Jan 30 14:59:30 2023 -0500

    Correctly detect shifts out of range
    
    get_shift_range was incorrectly communicating that it couldn't calculate
    a range when the shift values was always out fo range.  Fix this and
    alwasy return [0, 0] when the shift value is always out of range.
    
            PR tree-optimization/108306
            gcc/
            * range-op.cc (operator_lshift::fold_range): Return [0, 0] not
            varying for shifts that are always out of void range.
            (operator_rshift::fold_range): Return [0, 0] not
            varying for shifts that are always out of void range.
    
            gcc/testsuite/
            * gcc.dg/pr108306.c: New.

Diff:
---
 gcc/range-op.cc                 |  4 ++--
 gcc/testsuite/gcc.dg/pr108306.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index b5f4627fe2b..bf95f5fbaa1 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -1970,7 +1970,7 @@ operator_lshift::fold_range (irange &r, tree type,
       if (op2.undefined_p ())
 	r.set_undefined ();
       else
-	r.set_varying (type);
+	r.set_zero (type);
       return true;
     }
 
@@ -2240,7 +2240,7 @@ operator_rshift::fold_range (irange &r, tree type,
       if (op2.undefined_p ())
 	r.set_undefined ();
       else
-	r.set_varying (type);
+	r.set_zero (type);
       return true;
     }
 
diff --git a/gcc/testsuite/gcc.dg/pr108306.c b/gcc/testsuite/gcc.dg/pr108306.c
new file mode 100644
index 00000000000..1044c646de7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108306.c
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2  -fno-strict-overflow -fsanitize=shift -Warray-bounds" } */
+
+enum psi_task_count {
+	NR_IOWAIT,
+	NR_PSI_TASK_COUNTS = 4,
+};
+
+unsigned int tasks[NR_PSI_TASK_COUNTS];
+
+static void psi_group_change(unsigned int set)
+{
+	unsigned int t;
+	unsigned int state_mask = 0;
+
+	for (t = 0; set; set &= ~(1 << t), t++)
+		if (set & (1 << t))
+			tasks[t]++;
+}
+
+void psi_task_switch(int sleep)
+{
+	int set = 0;
+
+	if (sleep)
+		set |= (1 << NR_IOWAIT);
+
+	psi_group_change(set);
+}