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OP_SUBSTR_LEFT: GH#22914 - multiple pointers to replacement OP #22918

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Jan 16, 2025
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OP_SUBSTR_LEFT: GH#22914 - multiple pointers to replacement OP #22918

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17 changes: 11 additions & 6 deletions peep.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3869,7 +3869,7 @@ Perl_rpeep(pTHX_ OP *o)
break;

case OP_SUBSTR: {
OP *expr, *offs, *len;
OP *expr, *offs, *len, *repl = NULL;
/* Specialize substr($x, 0, $y) and substr($x,0,$y,"") */
/* Does this substr have 3-4 args and amiable flags? */
if (
Expand Down Expand Up @@ -3897,7 +3897,7 @@ Perl_rpeep(pTHX_ OP *o)

if (cMAXARG3x(o) == 4) {/* replacement */
/* Is the replacement string CONST ""? */
OP *repl = OpSIBLING(len);
repl = OpSIBLING(len);
if (repl->op_type != OP_CONST)
break;
SV *repl_sv = cSVOPx_sv(repl);
Expand All @@ -3908,12 +3908,10 @@ Perl_rpeep(pTHX_ OP *o)
break;
}
/* It's on! */
/* Take out the static LENGTH & REPLACMENT OPs */
/* Take out the static LENGTH OP. */
/* (The finalizer does not seem to change op_next here) */
expr->op_next = offs->op_next;
o->op_private = cMAXARG3x(o);
if (cMAXARG3x(o) == 4)
len->op_next = o;

/* We have a problem if padrange pushes the expr OP for us,
* then jumps straight to the offs CONST OP. For example:
Expand All @@ -3924,7 +3922,14 @@ Perl_rpeep(pTHX_ OP *o)
* B::Deparse. :/ */
op_null(offs);

/* repl status unchanged because it makes Deparsing easier. */
/* There can be multiple pointers to repl, see GH #22914.
* substr $x, 0, $y ? 2 : 3, "";
* So instead of rewriting all of len, null out repl. */
if (repl) {
op_null(repl);
/* We can still rewrite the simple len case though.*/
len->op_next = o;
}

/* Upgrade the SUBSTR to a SUBSTR_LEFT */
OpTYPE_set(o, OP_SUBSTR_LEFT);
Expand Down
7 changes: 7 additions & 0 deletions t/op/substr_left.t
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Expand Up @@ -104,5 +104,12 @@ $str = "\x00\x01\x02\x03\x04\x05";
$result = substr($str, 0, 3, "");
is($result, "\x00\x01\x02", 'hex EXPR: returns correct characters');
is($str, "\x03\x04\x05", 'hex EXPR: retains correct characters');
# GH #22914. LEN has more than one pointer to REPL.
$str = "perl";
# Hopefully $INC[0] ne '/dev/random' is a reasonable test assumption...
# (We need a condition that no future clever optimiser will strip)
$result = substr($str, 0, $INC[0] eq '/dev/random' ? 2: 3, '');
is($result, 'per', 'GH#22914: non-trivial LEN returns correct characters');
is($str, 'l', 'GH#22914: non-trivial LEN retains correct characters');

done_testing();
8 changes: 4 additions & 4 deletions t/perf/opcount.t
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Expand Up @@ -1034,15 +1034,15 @@ test_opcount(0, "substr with const zero offset and '' repl (void)",
{
substr => 0,
substr_left => 1,
const => 2,
const => 1,
});

test_opcount(0, "substr with const zero offset and '' repl (lexical)",
sub { my $z; my $x = substr($z, 0, 2, "") },
{
substr => 0,
substr_left => 1,
const => 2,
const => 1,
padsv => 3,
sassign => 1
});
Expand All @@ -1052,7 +1052,7 @@ test_opcount(0, "substr with const zero offset and '' repl (lexical TARGMY)",
{
substr => 0,
substr_left => 1,
const => 2,
const => 1,
padsv => 3,
padsv_store => 0,
sassign => 0
Expand All @@ -1063,7 +1063,7 @@ test_opcount(0, "substr with const zero offset and '' repl (gv)",
{
substr => 0,
substr_left => 1,
const => 2,
const => 1,
gvsv => 1,
sassign => 1
});
Expand Down
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