Porting/bench.pl: fix broken --bisect option

This option had bit-rotted: checks for the right number of perl executables
weren't taking account of --bisect.

Fix, and add tests.

2 files changed, 14 insertions, 3 deletions

diff --git a/Porting/bench.pl b/Porting/bench.pl
index 333835e3d9..bf1e32beb3 100755
--- a/Porting/bench.pl
+++ b/Porting/bench.pl
@@ -740,7 +740,7 @@ sub do_grind {
         my @run_perls= process_puts($perls, @$perl_args);
         push @$perls, @run_perls;
         die "Error: Not enough perls to run a report, and --write not specified.\n"
-            if @$perls < 2 and !$OPTS{write};
+            if @$perls < 2 and !($OPTS{write} || $OPTS{bisect});
         $results = grind_run($tests, $order, \@run_perls, $loop_counts, $results);
     }
 
@@ -776,7 +776,7 @@ sub do_grind {
         close $out       or die "Error: closing file '$OPTS{write}': $!\n";
     }
     if (!$OPTS{write} or $OPTS{show}) {
-        if (@$perls < 2 && !$OPTS{raw}) {
+        if (@$perls < 2 && !($OPTS{raw} || $OPTS{bisect})) {
             die "Error: need more than one perl to do a report.\n";
         }
         my ($processed, $averages) =
diff --git a/t/porting/bench.t b/t/porting/bench.t
index 46a293781b..2aa7d06245 100644
--- a/t/porting/bench.t
+++ b/t/porting/bench.t
@@ -93,7 +93,8 @@ ok -s $resultfile1, "--write should create a non-empty results file (1 perl)";
 
 note("running cachegrind for 2nd perl; may be slow...");
 $out = qx($bench_cmd -j 2 --read=$resultfile1 --write=$resultfile2 $^X=p1 2>&1);
-is length($out), 0, "--write should produce no output (2 perls)";
+is length($out), 0, "--write should produce no output (2 perls)"
+    or diag("got: $out");
 ok -s $resultfile2, "--write should create a non-empty results file (2 perls)";
 
 # 1 perl:
@@ -126,6 +127,16 @@ $out = qx($bench_cmd --read=$resultfile2 --compact=1 2>&1);
 like $out, $format_qrs{compact}, "basic cachegrind compact format; 2 perls";
 
 
+# bisect
+
+note("running cachegrind bisect on 1 perl; may be slow...");
+
+# the Ir range here is intended such that the bisect will always fail
+$out = qx($bench_cmd --tests=call::sub::empty --bisect=Ir,100000,100001 $^X=p0 2>&1);
+
+is $?, 1 << 8, "--bisect should not match";
+is length($out), 0, "--bisect should produce no output"
+    or diag("got: $out");
 
 done_testing();