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Prevent nested foreach unrolling to fix exponential blowup #5732

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Prevent nested foreach unrolling to fix exponential blowup #5732

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Prevent nested foreach unrolling to fix exponential blowup
staabm May 22, 2026
c82b6f0
Use factor-based nested foreach unroll limit instead of boolean flag
phpstan-bot May 23, 2026
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14 changes: 9 additions & 5 deletions src/Analyser/NodeScopeResolver.php
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Original file line number Diff line number Diff line change
Expand Up @@ -193,7 +193,7 @@ class NodeScopeResolver
private const LOOP_SCOPE_ITERATIONS = 3;
private const GENERALIZE_AFTER_ITERATION = 1;
private const FOREACH_UNROLL_LIMIT = 16;
private const FOREACH_UNROLL_NESTED_LIMIT = 16;
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@staabm staabm May 23, 2026 •
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instead of removing this feature as a whole, would it be enough to reduce the threshold to a lower value, so we can still have the more precise results in some cases.

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@phpstan-bot phpstan-bot May 23, 2026

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Done. Here's a summary of the changes:

Instead of completely disabling nested foreach unrolling, restored the factor-based approach with a lower limit:

  • FOREACH_UNROLL_NESTED_LIMIT = 8 (reduced from original 16) — only checked when already inside an unrolled foreach (factor > 1), so top-level foreaches are unaffected
  • The factor is now properly propagated through the final convergence pass via enterUnrolledForeach(totalKeys), fixing a bug in the original code where the final pass reset the factor to 1, allowing exponential re-unrolling
  • This allows 2-3 levels of nesting with small constant arrays while preventing the exponential blowup for deeper nesting
  • All three test cases (bug-7978, bug-9332, bug-14489) regain their precise type expectations
  • Benchmark (bug-14674.php with 13 nested levels) still completes in ~3.4s

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@staabm staabm May 23, 2026

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add a test which demonstrates the type degradation happens at the configured threshold

private const FOREACH_UNROLL_NESTED_LIMIT = 8;

/** @var array<string, true> filePath(string) => bool(true) */
private array $analysedFiles = [];
Expand Down Expand Up @@ -1450,6 +1450,7 @@ public function processStmtNode(

$originalStorage = $storage;
$unrolledEndScope = null;
$unrolledTotalKeys = null;
if ($context->isTopLevel()) {
$storage = $originalStorage->duplicate();

Expand All @@ -1458,6 +1459,7 @@ public function processStmtNode(
if ($unrolledResult !== null) {
$bodyScope = $unrolledResult['bodyScope'];
$unrolledEndScope = $unrolledResult['endScope'];
$unrolledTotalKeys = $unrolledResult['totalKeys'];
} else {
$bodyScope = $this->enterForeach($originalScope, $storage, $originalScope, $stmt, $nodeCallback);
$count = 0;
Expand Down Expand Up @@ -1486,7 +1488,8 @@ public function processStmtNode(
$bodyScope = $bodyScope->mergeWith($this->polluteScopeWithAlwaysIterableForeach ? $scope->filterByTruthyValue($arrayComparisonExpr) : $scope);
$storage = $originalStorage;
$bodyScope = $this->enterForeach($bodyScope, $storage, $originalScope, $stmt, $nodeCallback);
$finalScopeResult = $this->processStmtNodesInternal($stmt, $stmt->stmts, $bodyScope, $storage, $nodeCallback, $context)->filterOutLoopExitPoints();
$finalPassContext = $unrolledTotalKeys !== null ? $context->enterUnrolledForeach($unrolledTotalKeys) : $context;
$finalScopeResult = $this->processStmtNodesInternal($stmt, $stmt->stmts, $bodyScope, $storage, $nodeCallback, $finalPassContext)->filterOutLoopExitPoints();
$finalScope = $finalScopeResult->getScope();
$scopesWithIterableValueType = [];

Expand Down Expand Up @@ -4079,7 +4082,7 @@ public function processVarAnnotation(MutatingScope $scope, array $variableNames,
}

/**
* @return array{bodyScope: MutatingScope, endScope: MutatingScope}|null
* @return array{bodyScope: MutatingScope, endScope: MutatingScope, totalKeys: int}|null
*/
private function tryProcessUnrolledConstantArrayForeach(
Foreach_ $stmt,
Expand Down Expand Up @@ -4114,7 +4117,8 @@ private function tryProcessUnrolledConstantArrayForeach(
if ($totalKeys === 0 || $totalKeys > self::FOREACH_UNROLL_LIMIT) {
return null;
}
if ($context->getForeachUnrollFactor() * $totalKeys > self::FOREACH_UNROLL_NESTED_LIMIT) {
$foreachUnrollFactor = $context->getForeachUnrollFactor();
if ($foreachUnrollFactor > 1 && $foreachUnrollFactor * $totalKeys > self::FOREACH_UNROLL_NESTED_LIMIT) {
return null;
}

Expand Down Expand Up @@ -4242,7 +4246,7 @@ private function tryProcessUnrolledConstantArrayForeach(
$endScope = $endScope->mergeWith($breakScope);
}

return ['bodyScope' => $bodyScope, 'endScope' => $endScope];
return ['bodyScope' => $bodyScope, 'endScope' => $endScope, 'totalKeys' => $totalKeys];
}

private function getTraversableForeachThrowPoint(MutatingScope $scope, Expr $iteratee): ?InternalThrowPoint
Expand Down
83 changes: 83 additions & 0 deletions tests/bench/data/bug-14674.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,83 @@
<?php declare(strict_types = 1);

namespace Bug14674;

use PHPUnit\Framework\Attributes\DataProvider;
use PHPUnit\Framework\TestCase;

class PhpStanPerformanceTest extends TestCase {

/**
* @param \Closure $closure
*/
#[DataProvider('performanceProvider')]
public function testPerformance(\Closure $closure): void {
$this->assertTrue($closure());
}

/**
* @return iterable<string, array{closure: \Closure}>
*/
public static function performanceProvider(): iterable {
foreach(['0', '1'] as $level_1) {
$keys = [$level_1];

foreach(['0', '1'] as $level_2) {
$keys[] = $level_2;

foreach(['0', '1'] as $level_3) {
$keys[] = $level_3;

foreach(['0', '1'] as $level_4) {
$keys[] = $level_4;

foreach(['0', '1'] as $level_5) {
$keys[] = $level_5;

foreach(['0', '1'] as $level_6) {
$keys[] = $level_6;

foreach(['0', '1'] as $level_7) {
$keys[] = $level_7;

foreach(['0', '1'] as $level_8) {
$keys[] = $level_8;

foreach(['0', '1'] as $level_9) {
$keys[] = $level_9;

foreach(['0', '1'] as $level_10) {
$keys[] = $level_10;

foreach(['0', '1'] as $level_11) {
$keys[] = $level_11;

foreach(['0', '1'] as $level_12) {
$keys[] = $level_12;

foreach(['0', '1'] as $level_13) {
$keys[] = $level_13;

$case = [
'closure' => function () use ($level_1, $level_3, $level_5, $level_13) {
return $level_1 === '1' && $level_3 === '1' && $level_5 === '1' && $level_13 === '1';
},
];

yield implode('-', $keys) => $case;
}
}
}
}
}
}
}
}
}
}
}
}
}
}

}
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