From 4e82c85b1c9c9b30253b8624470da6f20a6c0604 Mon Sep 17 00:00:00 2001
From: Karl Williamson <khw@cpan.org>
Date: Mon, 15 Mar 2021 21:01:47 -0600
Subject: [PATCH] Fix broken left shift of IV_MIN under 'use integer'
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This fixes GH 18639

When I wrote this code, I conflated casting and complementing.

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 pp.c       | 3 ---
 t/op/bop.t | 9 ++++++++-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/pp.c b/pp.c
index d365afea4c..baf0777a47 100644
--- a/pp.c
+++ b/pp.c
@@ -2007,9 +2007,6 @@ static IV S_iv_shift(IV iv, int shift, bool left)
      * 18446744073709551552
      * */
     if (left) {
-        if (iv == IV_MIN) { /* Casting this to a UV is undefined behavior */
-            return 0;
-        }
         return (IV) (((UV) iv) << shift);
     }
 
diff --git a/t/op/bop.t b/t/op/bop.t
index 07f057d0a9..31b6531a03 100644
--- a/t/op/bop.t
+++ b/t/op/bop.t
@@ -18,7 +18,7 @@ BEGIN {
 # If you find tests are failing, please try adding names to tests to track
 # down where the failure is, and supply your new names as a patch.
 # (Just-in-time test naming)
-plan tests => 502;
+plan tests => 503;
 
 # numerics
 ok ((0xdead & 0xbeef) == 0x9ead);
@@ -33,6 +33,13 @@ ok ((33023 >> 7) == 257);
 # signed vs. unsigned
 ok ((~0 > 0 && do { use integer; ~0 } == -1));
 
+{   # GH #18639
+    my $iv_min = -(~0 >> 1) - 1;
+    my $shifted;
+    { use integer; $shifted = $iv_min << 0 };
+    is($shifted, $iv_min, "IV_MIN << 0 yields IV_MIN under 'use integer'");
+}
+
 my $bits = 0;
 for (my $i = ~0; $i; $i >>= 1) { ++$bits; }
 my $cusp = 1 << ($bits - 1);
-- 
2.26.3