Optimise out PUSHMARK/RETURN if return is the last statement in a sub.

This makes:

  sub baz { return $cat; }

Behave like:

  sub baz { $cat; }

Which is notably faster.

Unpatched:

  ./perl -Ilib/ ~/stuff/bench.pl
  Benchmark: timing 40000000 iterations of normal, ret...
    normal:  3 wallclock secs ( 1.60 usr +  0.01 sys =  1.61 CPU) @ 24844720.50/s (n=40000000)
       ret:  3 wallclock secs ( 2.08 usr +  0.00 sys =  2.08 CPU) @ 19230769.23/s (n=40000000)

Patched:

  ./perl -Ilib ~/stuff/bench.pl
  Benchmark: timing 40000000 iterations of aret, normal...
    normal:  2 wallclock secs ( 1.72 usr +  0.00 sys =  1.72 CPU) @ 23255813.95/s (n=40000000)
       ret:  2 wallclock secs ( 1.72 usr +  0.00 sys =  1.72 CPU) @ 23255813.95/s (n=40000000)

The difference in OP trees can be seen here:

Unpatched:

  $ perl  -MO=Concise,baz -e 'sub baz { return $cat }'
  main::baz:
  5  <1> leavesub[1 ref] K/REFC,1 ->(end)
  -     <@> lineseq KP ->5
  1        <;> nextstate(main 1 -e:1) v ->2
  4        <@> return K ->5
  2           <0> pushmark s ->3
  -           <1> ex-rv2sv sK/1 ->4
  3              <#> gvsv[*cat] s ->4
  -e syntax OK

Patched:

  $ ./perl -Ilib  -MO=Concise,baz -e 'sub baz { return $cat }'
  main::baz:
  3  <1> leavesub[1 ref] K/REFC,1 ->(end)
  -     <@> lineseq KP ->3
  1        <;> nextstate(main 1 -e:1) v ->2
  -        <@> return K ->-
  -           <0> pushmark s ->2
  -           <1> ex-rv2sv sK/1 ->-
  2              <$> gvsv(*cat) s ->3
  -e syntax OK

(Includes some modifications from Steffen)

1 files changed, 17 insertions, 1 deletions

diff --git a/ext/B/t/optree_samples.t b/ext/B/t/optree_samples.t
index 326e0ee617..a4f84c6e9f 100644
--- a/ext/B/t/optree_samples.t
+++ b/ext/B/t/optree_samples.t
@@ -14,7 +14,7 @@ BEGIN {
 }
 use OptreeCheck;
 use Config;
-plan tests	=> 34;
+plan tests	=> 37;
 
 pass("GENERAL OPTREE EXAMPLES");
 
@@ -637,6 +637,22 @@ EOT_EOT
 # 6  <@> leave[1 ref] vKP/REFC
 EONT_EONT
 
+pass("rpeep - return \$x at end of sub");
+
+checkOptree ( name	=> '-exec sub { return 1 }',
+	      code	=> sub { return 1 },
+	      bcopts	=> '-exec',
+	      strip_open_hints => 1,
+	      expect	=> <<'EOT_EOT', expect_nt => <<'EONT_EONT');
+# 1  <;> nextstate(main 1 -e:1) v
+# 2  <$> const[IV 1] s
+# 3  <1> leavesub[1 ref] K/REFC,1
+EOT_EOT
+# 1  <;> nextstate(main 1 -e:1) v
+# 2  <$> const(IV 1) s
+# 3  <1> leavesub[1 ref] K/REFC,1
+EONT_EONT
+
 __END__
 
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