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Fix GH-25061: $x = $x - 1 on null is optimized to PRE_DEC #25074

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Fix GH-25061: $x = $x - 1 on null is optimized to PRE_DEC #25074

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9636ca4
Fix GH-25061: $x = $x - 1 on null is optimized to PRE_DEC
lazerg Oct 31, 2026
1727b55
Add comment on the null exclusion in SUB to PRE_DEC rewrite
lazerg Oct 31, 2026
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6 changes: 4 additions & 2 deletions Zend/Optimizer/dfa_pass.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1359,7 +1359,8 @@ void zend_dfa_optimize_op_array(zend_op_array *op_array, zend_optimizer_ctx *ctx
&& Z_TYPE_P(CT_CONSTANT_EX(op_array, op_array->opcodes[op_2].op2.constant)) == IS_LONG
&& Z_LVAL_P(CT_CONSTANT_EX(op_array, op_array->opcodes[op_2].op2.constant)) == 1
&& ssa->ops[op_2].op1_use >= 0
&& !(ssa->var_info[ssa->ops[op_2].op1_use].type & (MAY_BE_FALSE|MAY_BE_TRUE|MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_OBJECT|MAY_BE_RESOURCE|MAY_BE_REF))) {
/* MAY_BE_UNDEF|MAY_BE_NULL is excluded because of the currently inconsistent behaviour, revisit in PHP 9 once it is fixed */
&& !(ssa->var_info[ssa->ops[op_2].op1_use].type & (MAY_BE_UNDEF|MAY_BE_NULL|MAY_BE_FALSE|MAY_BE_TRUE|MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_OBJECT|MAY_BE_RESOURCE|MAY_BE_REF))) {

op_array->opcodes[op_2].opcode = ZEND_PRE_DEC;
SET_UNUSED(op_array->opcodes[op_2].op2);
Expand Down Expand Up @@ -1513,7 +1514,8 @@ void zend_dfa_optimize_op_array(zend_op_array *op_array, zend_optimizer_ctx *ctx
&& Z_TYPE_P(CT_CONSTANT_EX(op_array, op_array->opcodes[op_2].op2.constant)) == IS_LONG
&& Z_LVAL_P(CT_CONSTANT_EX(op_array, op_array->opcodes[op_2].op2.constant)) == 1
&& ssa->ops[op_2].op1_use >= 0
&& !(ssa->var_info[ssa->ops[op_2].op1_use].type & (MAY_BE_FALSE|MAY_BE_TRUE|MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_OBJECT|MAY_BE_RESOURCE|MAY_BE_REF))) {
/* MAY_BE_UNDEF|MAY_BE_NULL is excluded because of the currently inconsistent behaviour, revisit in PHP 9 once it is fixed */
&& !(ssa->var_info[ssa->ops[op_2].op1_use].type & (MAY_BE_UNDEF|MAY_BE_NULL|MAY_BE_FALSE|MAY_BE_TRUE|MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_OBJECT|MAY_BE_RESOURCE|MAY_BE_REF))) {

op_array->opcodes[op_2].opcode = ZEND_PRE_DEC;
SET_UNUSED(op_array->opcodes[op_2].op2);
Expand Down
43 changes: 43 additions & 0 deletions ext/opcache/tests/opt/gh25061.phpt
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@@ -0,0 +1,43 @@
--TEST--
GH-25061 ($x = $x - 1 on null is optimized to PRE_DEC)
--EXTENSIONS--
opcache
--INI--
opcache.enable=1
opcache.enable_cli=1
opcache.optimization_level=-1
--FILE--
<?php

function nullable(?int $x)
{
$x = $x - 1;
return $x;
}

function undef()
{
$x = $x - 1;
return $x;
}

function twice(?int $x)
{
$x = $x - 1;
$x = $x - 1;
return $x;
}

var_dump(nullable(null));
var_dump(nullable(5));
var_dump(undef());
var_dump(twice(null));

?>
--EXPECTF--
int(-1)
int(4)

Warning: Undefined variable $x in %s on line %d
int(-1)
int(-2)
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