Use const repl optimisation with s///e where possible

In those cases where s///e contains a single variable or a sequence
that is folded to a const op, we can do away with substcont.

PMf_EVAL means that there was an /e.  But we don’t actually need to
check that; instead we can just examine the op tree, which we have to
do anyway.

The op tree that s//$x/e and s//"constant"/e compile down to have a
null (a do-block) containing a scope op (block with a single state-
ment, as opposed to op_leave which represents multiple statements)
containing a null followed by the constant or variable.

2 files changed, 8 insertions, 6 deletions

diff --git a/dist/B-Deparse/Deparse.pm b/dist/B-Deparse/Deparse.pm
index 2a768c0e5a..07386d5626 100644
--- a/dist/B-Deparse/Deparse.pm
+++ b/dist/B-Deparse/Deparse.pm
@@ -4726,19 +4726,19 @@ sub pp_subst {
     my $flags = "";
     my $pmflags = $op->pmflags;
     if (null($op->pmreplroot)) {
-	$repl = $self->dq($kid);
+	$repl = $kid;
 	$kid = $kid->sibling;
     } else {
 	$repl = $op->pmreplroot->first; # skip substcont
-	while ($repl->name eq "entereval") {
+    }
+    while ($repl->name eq "entereval") {
 	    $repl = $repl->first;
 	    $flags .= "e";
-	}
-	if ($pmflags & PMf_EVAL) {
+    }
+    if ($pmflags & PMf_EVAL) {
 	    $repl = $self->deparse($repl->first, 0);
-	} else {
+    } else {
 	    $repl = $self->dq($repl);	
-	}
     }
     my $extended = ($pmflags & PMf_EXTENDED);
     if (null $kid) {
diff --git a/dist/B-Deparse/t/deparse.t b/dist/B-Deparse/t/deparse.t
index 3500d5b38c..d1c6cb0a1f 100644
--- a/dist/B-Deparse/t/deparse.t
+++ b/dist/B-Deparse/t/deparse.t
@@ -322,6 +322,8 @@ my $foo = "Ab\x{100}\200\x{200}\237Cd\000Ef\x{1000}\cA\x{2000}\cZ";
 ####
 # s///e
 s/x/'y';/e;
+s/x/$a;/e;
+s/x/complex_expression();/e;
 ####
 # block
 { my $x; }