From 7f59654d9926053143b357cbca6f7a6d661051da Mon Sep 17 00:00:00 2001
From: James E Keenan <jkeenan@cpan.org>
Date: Wed, 7 Jun 2017 19:00:39 -0400
Subject: [PATCH 1/2] Add debugging statements to Benchmark::timeit() and
 ::runloop().

For: RT #131531
---
 lib/Benchmark.pm | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/lib/Benchmark.pm b/lib/Benchmark.pm
index 3eeba798730e..81c3054a45e5 100644
--- a/lib/Benchmark.pm
+++ b/lib/Benchmark.pm
@@ -699,7 +699,7 @@ sub runloop {
         $subref  = _doeval($subcode);
     }
     croak "runloop unable to compile '$c': $@\ncode: $subcode\n" if $@;
-    print STDERR "runloop $n '$subcode'\n" if $Debug;
+    print STDERR "XXX1: runloop $n '$subcode'\n" if $Debug;
 
     # Wait for the user timer to tick.  This makes the error range more like
     # -0.01, +0.  If we don't wait, then it's more like -0.01, +0.01.  This
@@ -719,10 +719,13 @@ sub runloop {
         for (my $i=0; $i < $limit; $i++) { my $x = $i / 1.5 } # burn user CPU
         $limit *= 1.1;
     }
+    print STDERR "XXX2:\n" if $Debug;
     $subref->();
+    print STDERR "XXX3:\n" if $Debug;
     $t1 = Benchmark->new($n);
     $td = &timediff($t1, $t0);
     timedebug("runloop:",$td);
+    print STDERR "XXX4:\n" if $Debug;
     $td;
 }
 
@@ -741,15 +744,19 @@ sub timeit {
     printf STDERR "timeit $n $code\n" if $Debug;
     my $cache_key = $n . ( ref( $code ) ? 'c' : 's' );
     if ($Do_Cache && exists $Cache{$cache_key} ) {
-	$wn = $Cache{$cache_key};
-    } else {
-	$wn = &runloop($n, ref( $code ) ? sub { } : '' );
-	# Can't let our baseline have any iterations, or they get subtracted
-	# out of the result.
-	$wn->[5] = 0;
-	$Cache{$cache_key} = $wn;
+        print STDERR "CCC: Why do I think I have a cache?\n" if $Debug;
+	    $wn = $Cache{$cache_key};
+    }
+    else {
+        print STDERR "AAA: About to call runloop for 'wn'\n" if $Debug;
+	    $wn = &runloop($n, ref( $code ) ? sub { } : '' );
+	    # Can't let our baseline have any iterations, or they get subtracted
+	    # out of the result.
+	    $wn->[5] = 0;
+	    $Cache{$cache_key} = $wn;
     }
 
+    print STDERR "BBB: About to call runloop for 'wc'\n" if $Debug;
     $wc = &runloop($n, $code);
 
     $wd = timediff($wc, $wn);

From 824df2b4512858176d3eb1633c14922be23cf028 Mon Sep 17 00:00:00 2001
From: James E Keenan <jkeenan@cpan.org>
Date: Wed, 7 Jun 2017 19:47:48 -0400
Subject: [PATCH 2/2] Add test file which is stripped-down version of
 lib/Benchmark.t.

What was bug report RT #131531 is now GH issue
https://github.com/Perl/perl5/issues/16003.
---
 lib/yBenchmark.t | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 lib/yBenchmark.t

diff --git a/lib/yBenchmark.t b/lib/yBenchmark.t
new file mode 100644
index 000000000000..15b6cdf681df
--- /dev/null
+++ b/lib/yBenchmark.t
@@ -0,0 +1,23 @@
+#!./perl -w
+# https://rt.perl.org/Ticket/Display.html?id=131531
+BEGIN {
+    chdir 't' if -d 't';
+    @INC = ('../lib');
+}
+
+use warnings;
+use strict;
+
+use Benchmark qw(:all);
+$Benchmark::Debug++;
+
+my $foo = 0;
+my $reps = 5;
+my $coderef = sub {++$foo};
+my $t = timeit($reps, $coderef);
+($t->isa('Benchmark'))
+    ? print "timeit CODEREF returned a Benchmark object\n"
+    : print "timeit CODEREF did NOT return a Benchmark object\n";
+($foo == $reps)
+    ? print "benchmarked code was run $reps times\n"
+    : print "FAIL: requested $reps reps, but $foo were run\n";