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peep.c: Only remove expected empty if/else block structures #23512

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peep.c: Only remove expected empty if/else block structures #23512

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119 changes: 94 additions & 25 deletions peep.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3590,41 +3590,110 @@ Perl_rpeep(pTHX_ OP *o)
case OP_COND_EXPR:
if (o->op_type == OP_COND_EXPR) {
OP *stub = cLOGOP->op_other;
OP *trueop = OpSIBLING( cLOGOP->op_first );
OP *falseop = OpSIBLING(trueop);

/* Is there an empty "if" block or ternary true branch?
If so, optimise away the OP_STUB if safe to do so. */
if (stub->op_type == OP_STUB &&
((stub->op_flags & OPf_WANT) != OPf_WANT_SCALAR)
) {
OP *trueop = OpSIBLING( cLOGOP->op_first );

assert((stub == trueop ) || (OP_TYPE_IS(trueop, OP_SCOPE) &&
((stub == cUNOPx(trueop)->op_first)) && !OpSIBLING(stub))
);
assert(!(stub->op_flags & OPf_KIDS));

cLOGOP->op_other = (stub->op_next == trueop) ?
stub->op_next->op_next :
stub->op_next;

op_sibling_splice(o, cLOGOP->op_first, 1, NULL);

if (stub != trueop) op_free(stub);
op_free(trueop);
} else
if (stub == trueop) {
/* This is very unlikely:
* cond_expr
* -condition-
* stub
* -else-
*/
assert(!(stub->op_flags & OPf_KIDS));
cLOGOP->op_other = stub->op_next;
op_sibling_splice(o, cLOGOP->op_first, 1, NULL);
op_free(stub);
break;
} else if (OP_TYPE_IS(trueop, OP_SCOPE) &&
(stub == cUNOPx(trueop)->op_first) ) {
assert(!(stub->op_flags & OPf_KIDS));

OP *stubsib = OpSIBLING(stub);
if (!stubsib) {
/* cond_expr
* -condition-
* scope
* stub
* -else-
*/
cLOGOP->op_other = trueop->op_next;
op_sibling_splice(o, cLOGOP->op_first, 1, NULL);
op_free(stub);
op_free(trueop);
break;
} else {
/* Could be something like this:
* -condition-
* scope
* stub
* null
* -else-
* But it may be more desirable (but is less
* straightforward) to transform this earlier
* in the compiler. Ignoring it for now,
* pending further exploration. */
}
}
}

/* Is there an empty "else" block or ternary false branch?
If so, optimise away the OP_STUB if safe to do so. */
stub = o->op_next;
if (stub->op_type == OP_STUB &&
((stub->op_flags & OPf_WANT) != OPf_WANT_SCALAR)
) {
assert(stub == OpSIBLING(OpSIBLING( cLOGOP->op_first )));
assert(!(stub->op_flags & OPf_KIDS));
o->op_flags |= OPf_SPECIAL; /* For B::Deparse */
o->op_next = stub->op_next;
op_sibling_splice(o, OpSIBLING(cLOGOP->op_first), 1, NULL);
op_free(stub);
if ((stub->op_flags & OPf_WANT) != OPf_WANT_SCALAR) {
if (stub->op_type == OP_STUB && !OpSIBLING(stub) ){
OP *stubsib = OpSIBLING(stub);
if ((stub == falseop) && !stubsib) {
/* cond_expr
* -condition-
* - if -
* stub
*/
assert(!(stub->op_flags & OPf_KIDS));
o->op_flags |= OPf_SPECIAL; /* For B::Deparse */
o->op_next = stub->op_next;
op_sibling_splice(o, OpSIBLING(cLOGOP->op_first), 1, NULL);
op_free(stub);
} else { /* Unexpected */ }
} else if (OP_TYPE_IS(stub,OP_ENTER) &&
OP_TYPE_IS(falseop, OP_LEAVE)) {
OP *enter = stub;
OP *stub = OpSIBLING(enter);
if (stub && OP_TYPE_IS(stub, OP_STUB) ){
assert(!(stub->op_flags & OPf_KIDS));
OP *stubsib = OpSIBLING(stub);
assert(stubsib);
if (OP_TYPE_IS(stubsib, OP_NULL) &&
!OpSIBLING(stubsib) &&
!(stubsib->op_flags & OPf_KIDS) ) {
/* cond_expr
* -condition-
* - if -
* leave
* enter
* stub
* null
*/
/* Ignoring it for now, pending further exploration.*/
/*
o->op_flags |= OPf_SPECIAL; // For B::Deparse
o->op_next = falseop->op_next;
op_sibling_splice(o, OpSIBLING(cLOGOP->op_first), 1, NULL);
op_free(enter);
op_free(stub);
op_free(stubsib);
op_free(falseop);
*/
}
}
}
}

}
/* FALLTHROUGH */
case OP_MAPWHILE:
Expand Down
15 changes: 14 additions & 1 deletion t/perf/opcount.t
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Original file line number Diff line number Diff line change
Expand Up @@ -1233,13 +1233,26 @@ test_opcount(0, "defined(ABC) gets constant folded",
defined => 0,
});

# Empty condop other/next branch optimizations
test_opcount(0, "Empty if{} blocks are optimised away",
sub { my $x; if ($x) { } else { 1 } },
{
stub => 0
});

test_opcount(0, "Empty else{} blocks are optimised away",
sub { my $x; if ($x) { 1 } else { } },
{
stub => 0
});

test_opcount(0, "Empty ternary true blocks are optimised away",
sub { my $x; ($x) ? () : 1 },
{
stub => 0
});

test_opcount(0, "Empty else{} blocks are optimised away",
test_opcount(0, "Empty ternary false blocks are optimised away",
sub { my $x; ($x) ? 1 : () },
{
stub => 0
Expand Down
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