[OptionsResolver] Optimize splitOutsideParenthesis() - 5.9x faster #61239

bendavies · 2025-07-25T16:09:21Z

Q	A
Branch?	7.4
Bug fix?	no
New feature?	no
Deprecations?	no
Issues	Fix #59354
License	MIT

This PR optimises the splitOutsideParenthesis method in OptionsResolver.php, achieving a 5.9x performance improvement.

I discovered this method as a performance hotspot while benchmarking a large Symfony form with many fields. Profiling revealed that splitOutsideParenthesis was consuming a significant portion of the form processing time.

The splitOutsideParenthesis method (introduced in PR #59354) is called frequently during options resolution and has several performance bottlenecks:

Character-by-character string concatenation creates new string objects on each iteration (particularly inefficient in PHP due to copy-on-write behavior)
All input strings are processed the same way, regardless of complexity - no fast path for simple types
Multiple conditional checks per character

Test Methodology

Here's how all performance measurements were conducted:

Benchmark tool: hyperfine (10 runs with 1 warmup run)
Test iterations: 100,000 iterations per test case
Test data: 16 different type patterns:
- Simple types: string, int, bool, array
- Union types: string|int, string|int|bool, string|int|bool|array
- Parentheses types: string|(int|bool), (string|int)|bool
- Nested types: string|(int|(bool|float)), (string|int)|(bool|float)
- Array types: string[], int[]
- Class types: MyClass, \\Namespace\\Class
- Complex union: string|int|bool|array|object|resource|callable

Each optimisation was tested in isolation to measure its individual impact, then all optimisations were combined for the final benchmark.

Optimisations

1. Fast Path for Simple Types (No Pipes)

Most type declarations are simple types like string, int, MyClass, etc. without any union types.

Implementation:

if (!\str_contains($type, '|')) {
    return [$type];
}

2. Fast Path for Union Types (No Parentheses)

Common union types like string|int|bool don't need complex parsing - PHP's explode() is much faster.

Implementation:

if (!\str_contains($type, '(') && !\str_contains($type, ')')) {
    return \explode('|', $type);
}

3. Eliminate String Concatenation

String concatenation in loops creates memory overhead. Using substr() avoids creating intermediate strings.

Implementation:

// Instead of: $currentPart .= $char;
// Use: $parts[] = \substr($type, $start, $i - $start);

4. Switch Statement Optimisation

Eliminates Multiple conditional checks per character.

Implementation:

switch ($char) {
    case '(':
        ++$parenthesisLevel;
        break;
    case ')':
        --$parenthesisLevel;
        break;
    case '|':
        // ...
}

Benchmark Results

Individual Optimisation Impact

Testing each optimisation in isolation:

hyperfine --warmup 1 --runs 10 \
  --sort=command \
  --reference 'php test_original.php' \
  'php test_opt1_fast_path_simple.php' \
  'php test_opt2_fast_path_union.php' \
  'php test_opt3_no_string_concat.php'  \
  'php test_opt4_switch_statement.php'

Relative speed comparison
        1.00          php test_original.php
        1.23 ±  0.02  php test_opt1_fast_path_simple.php
        1.95 ±  0.04  php test_opt2_fast_path_union.php
        1.13 ±  0.03  php test_opt3_no_string_concat.php
        1.35 ±  0.03  php test_opt4_switch_statement.php

Combined Optimisation Impact

Combining all optimisations:

hyperfine --warmup 1 --runs 10 \
  --sort=command \
  --reference 'php test_original.php' \
  'php test_optimised.php'

Relative speed comparison
        1.00          php test_original.php
        2.91 ±  0.03  php test_optimised.php

Further Optimization: Regex Solution

After achieving the 2.91x improvement with manual optimizations, I explored regex-based solutions for even better performance as suggested by @dunglas.
The challenge was maintaining correctness for deeply nested union types.

Final Solution: Recursive Regex

The solution uses PCRE's (?(DEFINE) syntax to create a recursive pattern supporting unlimited nesting:

Final Benchmark Results

hyperfine --warmup 1 --runs 10 --reference 'php test_original.php' \
  'php test_optimized.php' 'php test_recursive_final.php'

Summary
  php test_original.php ran
    5.85 ± 0.11 times slower than php test_recursive_final.php
    2.57 ± 0.12 times slower than php test_optimized.php

alexandre-daubois

Performance improvements are refactors, which means this should target 7.4. 7.3 being already released, the branch receives bug fixes only.

Also, would you mind sharing the test set you used to run benchmarks? In addition to the methodology used as explained in the description, having the opportunity to see the benchmark code would be a plus!

src/Symfony/Component/OptionsResolver/OptionsResolver.php

yceruto · 2025-07-25T16:21:24Z

Hey @bendavies thanks for this optimization proposal! For performance refactoring PRs, we usually target the latest dev branch, in this case, 7.4

bendavies · 2025-07-25T16:45:27Z

Performance improvements are refactors, which means this should target 7.4. 7.3 being already released, the branch receives bug fixes only.

Also, would you mind sharing the test set you used to run benchmarks? In addition to the methodology used as explained in the description, having the opportunity to see the benchmark code would be a plus!

# Test individual optimizations
hyperfine --warmup 1 --runs 10 \
  --reference 'php test_original.php' \
  'php test_opt1_fast_path_simple.php' \
  'php test_opt2_fast_path_union.php' \
  'php test_opt3_no_string_concat.php' \
  'php test_opt4_switch_statement.php'

# Test combined optimization
hyperfine --warmup 1 --runs 10 \
  --reference 'php test_original.php' \
  'php test_optimized.php'

test_original.php - Original implementation

<?php

function splitOutsideParenthesis(string $type): array
{
    $parts = [];
    $currentPart = '';
    $parenthesisLevel = 0;

    $typeLength = \strlen($type);
    for ($i = 0; $i < $typeLength; ++$i) {
        $char = $type[$i];

        if ('(' === $char) {
            ++$parenthesisLevel;
        } elseif (')' === $char) {
            --$parenthesisLevel;
        }

        if ('|' === $char && 0 === $parenthesisLevel) {
            $parts[] = $currentPart;
            $currentPart = '';
        } else {
            $currentPart .= $char;
        }
    }

    if ('' !== $currentPart) {
        $parts[] = $currentPart;
    }

    return $parts;
}

$testCases = [
    'string',
    'int',
    'bool',
    'array',
    'string|int',
    'string|int|bool',
    'string|int|bool|array',
    'string|(int|bool)',
    '(string|int)|bool',
    'string|(int|(bool|float))',
    '(string|int)|(bool|float)',
    'MyClass',
    'string[]',
    'int[]',
    '\\Namespace\\Class',
    'string|int|bool|array|object|resource|callable',
];

$iterations = 100000;

$start = microtime(true);

for ($i = 0; $i < $iterations; $i++) {
    foreach ($testCases as $testCase) {
        splitOutsideParenthesis($testCase);
    }
}

$end = microtime(true);
$duration = ($end - $start) * 1000;

$peakMemory = memory_get_peak_usage(true) / 1024 / 1024;

echo "Original implementation: " . number_format($duration, 2) . "ms for " . ($iterations * count($testCases)) . " operations\n";
echo "Peak memory usage: " . number_format($peakMemory, 2) . " MB\n";

test_opt1_fast_path_simple.php - Optimization 1: Fast path for simple types

<?php

function splitOutsideParenthesis(string $type): array
{
    if (!\str_contains($type, '|')) {
        return [$type];
    }
    
    $parts = [];
    $currentPart = '';
    $parenthesisLevel = 0;

    $typeLength = \strlen($type);
    for ($i = 0; $i < $typeLength; ++$i) {
        $char = $type[$i];

        if ('(' === $char) {
            ++$parenthesisLevel;
        } elseif (')' === $char) {
            --$parenthesisLevel;
        }

        if ('|' === $char && 0 === $parenthesisLevel) {
            $parts[] = $currentPart;
            $currentPart = '';
        } else {
            $currentPart .= $char;
        }
    }

    if ('' !== $currentPart) {
        $parts[] = $currentPart;
    }

    return $parts;
}

$testCases = [
    'string',
    'int',
    'bool',
    'array',
    'string|int',
    'string|int|bool',
    'string|int|bool|array',
    'string|(int|bool)',
    '(string|int)|bool',
    'string|(int|(bool|float))',
    '(string|int)|(bool|float)',
    'MyClass',
    'string[]',
    'int[]',
    '\\Namespace\\Class',
    'string|int|bool|array|object|resource|callable',
];

$iterations = 100000;

$start = microtime(true);

for ($i = 0; $i < $iterations; $i++) {
    foreach ($testCases as $testCase) {
        splitOutsideParenthesis($testCase);
    }
}

$end = microtime(true);
$duration = ($end - $start) * 1000;

$peakMemory = memory_get_peak_usage(true) / 1024 / 1024;

echo "Optimization 1 (fast path simple): " . number_format($duration, 2) . "ms for " . ($iterations * count($testCases)) . " operations\n";
echo "Peak memory usage: " . number_format($peakMemory, 2) . " MB\n";

test_opt2_fast_path_union.php - Optimization 2: Fast path for union types

<?php

function splitOutsideParenthesis(string $type): array
{
    if (!\str_contains($type, '(') && !\str_contains($type, ')')) {
        return \explode('|', $type);
    }

    $parts = [];
    $currentPart = '';
    $parenthesisLevel = 0;

    $typeLength = \strlen($type);
    for ($i = 0; $i < $typeLength; ++$i) {
        $char = $type[$i];

        if ('(' === $char) {
            ++$parenthesisLevel;
        } elseif (')' === $char) {
            --$parenthesisLevel;
        }

        if ('|' === $char && 0 === $parenthesisLevel) {
            $parts[] = $currentPart;
            $currentPart = '';
        } else {
            $currentPart .= $char;
        }
    }

    if ('' !== $currentPart) {
        $parts[] = $currentPart;
    }

    return $parts;
}

$testCases = [
    'string',
    'int',
    'bool',
    'array',
    'string|int',
    'string|int|bool',
    'string|int|bool|array',
    'string|(int|bool)',
    '(string|int)|bool',
    'string|(int|(bool|float))',
    '(string|int)|(bool|float)',
    'MyClass',
    'string[]',
    'int[]',
    '\\Namespace\\Class',
    'string|int|bool|array|object|resource|callable',
];

$iterations = 100000;

$start = microtime(true);

for ($i = 0; $i < $iterations; $i++) {
    foreach ($testCases as $testCase) {
        splitOutsideParenthesis($testCase);
    }
}

$end = microtime(true);
$duration = ($end - $start) * 1000;

$peakMemory = memory_get_peak_usage(true) / 1024 / 1024;

echo "Optimization 2 (fast path union): " . number_format($duration, 2) . "ms for " . ($iterations * count($testCases)) . " operations\n";
echo "Peak memory usage: " . number_format($peakMemory, 2) . " MB\n";

test_opt3_no_string_concat.php - Optimization 3: Eliminate string concatenation

<?php

function splitOutsideParenthesis(string $type): array
{
    $parts = [];
    $start = 0;
    $parenthesisLevel = 0;
    $length = \strlen($type);
    
    for ($i = 0; $i < $length; ++$i) {
        $char = $type[$i];

        if ('(' === $char) {
            ++$parenthesisLevel;
        } elseif (')' === $char) {
            --$parenthesisLevel;
        } elseif ('|' === $char && 0 === $parenthesisLevel) {
            $parts[] = \substr($type, $start, $i - $start);
            $start = $i + 1;
        }
    }

    if ($start < $length) {
        $parts[] = \substr($type, $start);
    }
    
    return $parts;
}

$testCases = [
    'string',
    'int',
    'bool',
    'array',
    'string|int',
    'string|int|bool',
    'string|int|bool|array',
    'string|(int|bool)',
    '(string|int)|bool',
    'string|(int|(bool|float))',
    '(string|int)|(bool|float)',
    'MyClass',
    'string[]',
    'int[]',
    '\\Namespace\\Class',
    'string|int|bool|array|object|resource|callable',
];

$iterations = 100000;

$start = microtime(true);

for ($i = 0; $i < $iterations; $i++) {
    foreach ($testCases as $testCase) {
        splitOutsideParenthesis($testCase);
    }
}

$end = microtime(true);
$duration = ($end - $start) * 1000;

$peakMemory = memory_get_peak_usage(true) / 1024 / 1024;

echo "Optimization 3 (no string concat): " . number_format($duration, 2) . "ms for " . ($iterations * count($testCases)) . " operations\n";
echo "Peak memory usage: " . number_format($peakMemory, 2) . " MB\n";

test_opt4_switch_statement.php - Optimization 4: Switch statement

<?php

function splitOutsideParenthesis(string $type): array
{
    $parts = [];
    $currentPart = '';
    $parenthesisLevel = 0;

    $typeLength = \strlen($type);
    for ($i = 0; $i < $typeLength; ++$i) {
        $char = $type[$i];

        switch ($char) {
            case '(':
                ++$parenthesisLevel;
                $currentPart .= $char;
                break;
            case ')':
                --$parenthesisLevel;
                $currentPart .= $char;
                break;
            case '|':
                if (0 === $parenthesisLevel) {
                    $parts[] = $currentPart;
                    $currentPart = '';
                } else {
                    $currentPart .= $char;
                }
                break;
            default:
                $currentPart .= $char;
                break;
        }
    }

    if ('' !== $currentPart) {
        $parts[] = $currentPart;
    }

    return $parts;
}

$testCases = [
    'string',
    'int',
    'bool',
    'array',
    'string|int',
    'string|int|bool',
    'string|int|bool|array',
    'string|(int|bool)',
    '(string|int)|bool',
    'string|(int|(bool|float))',
    '(string|int)|(bool|float)',
    'MyClass',
    'string[]',
    'int[]',
    '\\Namespace\\Class',
    'string|int|bool|array|object|resource|callable',
];

$iterations = 100000;

$start = microtime(true);

for ($i = 0; $i < $iterations; $i++) {
    foreach ($testCases as $testCase) {
        splitOutsideParenthesis($testCase);
    }
}

$end = microtime(true);
$duration = ($end - $start) * 1000;

$peakMemory = memory_get_peak_usage(true) / 1024 / 1024;

echo "Optimization 4 (switch statement): " . number_format($duration, 2) . "ms for " . ($iterations * count($testCases)) . " operations\n";
echo "Peak memory usage: " . number_format($peakMemory, 2) . " MB\n";

test_optimized.php - Final optimized implementation (all optimizations combined)

<?php

function splitOutsideParenthesis(string $type): array
{
    if (!\str_contains($type, '|')) {
        return [$type];
    }
    
    if (!\str_contains($type, '(') && !\str_contains($type, ')')) {
        return \explode('|', $type);
    }
    
    $parts = [];
    $start = 0;
    $parenthesisLevel = 0;
    $length = \strlen($type);
    
    for ($i = 0; $i < $length; ++$i) {
        $char = $type[$i];
        
        switch ($char) {
            case '(':
                ++$parenthesisLevel;
                break;
            case ')':
                --$parenthesisLevel;
                break;
            case '|':
                if (0 === $parenthesisLevel) {
                    $parts[] = \substr($type, $start, $i - $start);
                    $start = $i + 1;
                }
                break;
        }
    }
    
    if ($start < $length) {
        $parts[] = \substr($type, $start);
    }
    
    return $parts;
}

$testCases = [
    'string',
    'int',
    'bool',
    'array',
    'string|int',
    'string|int|bool',
    'string|int|bool|array',
    'string|(int|bool)',
    '(string|int)|bool',
    'string|(int|(bool|float))',
    '(string|int)|(bool|float)',
    'MyClass',
    'string[]',
    'int[]',
    '\\Namespace\\Class',
    'string|int|bool|array|object|resource|callable',
];

$iterations = 100000;

$start = microtime(true);

for ($i = 0; $i < $iterations; $i++) {
    foreach ($testCases as $testCase) {
        splitOutsideParenthesis($testCase);
    }
}

$end = microtime(true);
$duration = ($end - $start) * 1000;

$peakMemory = memory_get_peak_usage(true) / 1024 / 1024;

echo "Optimized implementation: " . number_format($duration, 2) . "ms for " . ($iterations * count($testCases)) . " operations\n";
echo "Peak memory usage: " . number_format($peakMemory, 2) . " MB\n";

src/Symfony/Component/OptionsResolver/OptionsResolver.php

bendavies · 2025-07-26T21:39:56Z

i investigated @dunglas suggestion to use regex.
a pure regex solution appears to be almost twice as fast as my current solution.
I'll update this PR on Monday

Summary
  php test_original.php ran
    5.53 ± 0.15 times slower than php test_optimized_v2.php <-- pure regex, no loops
    3.12 ± 0.08 times slower than php test_optimized.php

bendavies · 2025-07-29T15:29:31Z

@dunglas pure regex solution added. reproducing commit message here for completeness:

[OptionsResolver] optimize splitOutsideParenthesis with regex (5.88x faster)

Replace manual string parsing with regex-based implementation using PCRE's
(*SKIP)(*FAIL) backtracking control verbs. This approach:

Achieves 5.88x performance improvement over the original implementation

The regex pattern '\([^()]*(?:\([^()]*\)[^()]*)*\)(*SKIP)(*FAIL)|\|' works by:
 1. Matching parentheses and their contents (including nested parentheses)
 2. Using (*SKIP)(*FAIL) to skip these matches entirely
 3. Then splitting on the remaining pipe characters outside parentheses

nicolas-grekas · 2025-07-29T18:13:10Z

src/Symfony/Component/OptionsResolver/OptionsResolver.php

+                | # OR
+
+                \| # Match the pipe delimiter. This will only be matched if it was not inside a skipped group.
+                /x


can you try using a recursive regexp? this will remove the current limitation of parsing only the first 2 levels of nesting:

/ # Match a recursively balanced parenthetical group, then skip it \( # Match an opening parenthesis (?: # Start a non-capturing group for the contents [^()] # Match any character that is not a parenthesis | # OR (?R) # Recurse the entire pattern to match a nested group )* # Repeat the group for all contents \) # Match the final closing parenthesis (*SKIP)(*FAIL) # Discard the match and find the next one | # OR \| # Match the pipe delimiter (only if not inside a skipped group) /x

this didnt work because i think (?R) is trying to match the entire pattern (including the (*SKIP)(*FAIL) part i think?

fixed it by defining a recursive subroutine.

OskarStark · 2025-07-29T18:23:49Z

PR title and body would need an update then for the 5. optimization

bendavies · 2025-07-29T20:06:23Z

Got a bit scared after @nicolas-grekas pointed out that my regex only worked for 2 levels, so added a bunch of regression tests a first commit.

then added a new recursive regex which supports unlimited depth while maintaining the performance improvement.

nicolas-grekas · 2025-07-29T20:10:29Z

Thank you @bendavies.

bendavies · 2025-07-29T20:12:03Z

@nicolas-grekas sheesh that was fast 😆. I didn't have time to update the PR body

nicolas-grekas · 2025-07-29T20:13:51Z

You can still do it after the merge ;)

bendavies requested a review from yceruto as a code owner July 25, 2025 16:09

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bendavies force-pushed the optionresolver-splitOutsideParenthesis-performance branch from 1312319 to e01b177 Compare July 25, 2025 16:10

bendavies changed the title ~~[OptionsResolver] Optimize splitOutsideParenthesis() - 2.90x faster~~ [OptionsResolver] Optimize splitOutsideParenthesis() - 2.91x faster Jul 25, 2025

bendavies changed the base branch from 7.4 to 7.3 July 25, 2025 16:11

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bendavies requested review from xabbuh, lyrixx, dunglas, welcoMattic, kbond, chalasr, OskarStark and jderusse as code owners July 25, 2025 16:26

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bendavies changed the title ~~[OptionsResolver] Optimize splitOutsideParenthesis() - 2.91x faster~~ [OptionsResolver] Optimize splitOutsideParenthesis() - 5.9x faster Jul 29, 2025

[OptionsResolver] Optimize splitOutsideParenthesis() - 5.9x faster

b568fef

nicolas-grekas force-pushed the optionresolver-splitOutsideParenthesis-performance branch from 3aa0c9d to b568fef Compare July 29, 2025 20:10

nicolas-grekas merged commit 9977966 into symfony:7.4 Jul 29, 2025
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[OptionsResolver] Optimize splitOutsideParenthesis() - 5.9x faster #61239

[OptionsResolver] Optimize splitOutsideParenthesis() - 5.9x faster #61239

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Test Methodology

Optimisations

1. Fast Path for Simple Types (No Pipes)

2. Fast Path for Union Types (No Parentheses)

3. Eliminate String Concatenation

4. Switch Statement Optimisation

Benchmark Results

Individual Optimisation Impact

Combined Optimisation Impact

Further Optimization: Regex Solution

Final Solution: Recursive Regex

Final Benchmark Results

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