From 5b80069c7e65a3ed60ee16deac4a450a9c32efa6 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <aldyh@redhat.com>
Date: Mon, 19 Oct 2020 09:48:27 +0200
Subject: [PATCH] Handle right shifts by zero in range-ops.

If the shift amount in operator_lshift::op1_range was zero, an invalid range
of [1, 0] was being created.

gcc/ChangeLog:

	PR tree-optimization/97467
	* range-op.cc (operator_lshift::op1_range): Handle shifts by 0.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr97467.c: New test.
---
 gcc/range-op.cc                |  5 +++++
 gcc/testsuite/gcc.dg/pr97467.c | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr97467.c

diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index 0efa00186e8..30d2a4d3987 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -1579,6 +1579,11 @@ operator_lshift::op1_range (irange &r,
       wide_int shift = wi::to_wide (shift_amount);
       if (wi::lt_p (shift, 0, SIGNED))
 	return false;
+      if (shift == 0)
+	{
+	  r = lhs;
+	  return true;
+	}
 
       // Work completely in unsigned mode to start.
       tree utype = type;
diff --git a/gcc/testsuite/gcc.dg/pr97467.c b/gcc/testsuite/gcc.dg/pr97467.c
new file mode 100644
index 00000000000..dcbd218f733
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr97467.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+int a;
+long b;
+unsigned int c = 1;
+
+int main () {
+  int e;
+  for (; c <= 0; c++) {
+    int f = 0;
+    b = e;
+    a = f || b << c;
+  }
+  return 0;
+}
-- 
2.30.2