fix common assign issue on @a = (split(), 1)

RT #127999 Slowdown in split + list assign

The compile-time common-value detection mechanism for OP_ASSIGN
was getting OP_SPLIT wrong.

It was assuming that OP_SPLIT was always dangerous. In fact,
OP_SPLIT is usually completely safe, not passing though any of its
arguments, except where the assign in (@a = split()) has been optimised
away and the array attached directly to the OP_SPLIT op, or the ops that
produce the array have been appended as an extra child of the OP_SPLIT op
(OPf_STACKED).

2 files changed, 11 insertions, 1 deletions

diff --git a/t/perf/benchmarks b/t/perf/benchmarks
index f02a06a299..56987bcf27 100644
--- a/t/perf/benchmarks
+++ b/t/perf/benchmarks
@@ -993,6 +993,11 @@
         setup   => 'my $s = "abc:def"; my $r = []',
         code    => '@$r = split /:/, $s, 2;',
     },
+    'func::split::arraylist' => {
+        desc    => 'split into an array with extra arg',
+        setup   => 'my @a; my $s = "abc:def";',
+        code    => '@a = (split(/:/, $s, 2), 1);',
+    },
 
 
     'loop::block' => {
diff --git a/t/perf/optree.t b/t/perf/optree.t
index a2ff7f283c..49959ce666 100644
--- a/t/perf/optree.t
+++ b/t/perf/optree.t
@@ -10,7 +10,7 @@ BEGIN {
     @INC = '../lib';
 }
 
-plan 54;
+plan 59;
 
 use v5.10; # state
 use B qw(svref_2object
@@ -74,6 +74,11 @@ for my $test (
     [ "---", '(undef,$x) = f()', 'single scalar on LHS' ],
     [ "---", '($x,$y) = ($x)', 'single scalar on RHS, no AGG' ],
     [ "--A", '($x,@b) = ($x)', 'single scalar on RHS' ],
+    [ "--A", 'my @a; @a = (@a = split())',      'split a/a'   ],
+    [ "--A", 'my (@a,@b); @a = (@b = split())', 'split a/b'   ],
+    [ "---", 'my @a; @a = (split(), 1)',        '(split(),1)' ],
+    [ "---", '@a = (split(//, @a), 1)',         'split(@a)'   ],
+    [ "--A", 'my @a; my $ar = @a; @a = (@$ar = split())', 'a/ar split'  ],
 ) {
     my ($exp, $code, $desc) = @$test;
     my $sub = eval "sub { $code }"