[PHP] Recompile PHP.wasm ASYNCIFY with MAIN_MODULE set to 2

[mho22]

Motivation for the change, related issues

Following-up on : #3332

This pull request sets MAIN_MODULE=2 to PHP.wasm Node Asyncify and PHP.wasm Web Asyncify.

Implementation details

1. Updated the php/Dockerfile script to enable MAIN_MODULE=2 by default.

2. Ran the following commands

nx run php-wasm-compile-shared-intl:node:asyncify:all
nx run php-wasm-compile-shared-xdebug:asyncify:all
nx run php-wasm-node:recompile-php:asyncify:all

nx run php-wasm-compile-shared-intl:web:asyncify:all
nx run php-wasm-web:recompile-php:asyncify:all

Now the entire PHP.wasm builds are dead code eliminated. 🎉

Size Reduction

Metric	Before	After	Saved
Total binary size	888 MB	766 MB	122 MB (13.7%)
.wasm files	680 MB	571 MB	109 MB (16%)
JS glue code	22.7 MB	8.2 MB	14.5 MB (63%)

Per-version .wasm reduction

PHP Version	Before (avg)	After (avg)	Reduction
7.4	~20 MB	~17 MB	17–19%
8.0	~21 MB	~17 MB	17–19%
8.1	~24 MB	~20 MB	15–17%
8.2	~25 MB	~21 MB	15–17%
8.3	~25 MB	~21 MB	15–17%
8.4	~27 MB	~23 MB	14–16%
8.5	~28 MB	~24 MB	14–15%

Web vs Node Build Comparison

Platform	Before	After	Saved	Reduction
Node builds	468.8 MB	402.2 MB	66.6 MB	14.2%
Web builds	419.4 MB	364.0 MB	55.4 MB	13.2%

Breakdown by file type

Platform	.wasm saved	JS glue saved	.so delta
Node builds	59.4 MB (16.5%)	8.0 MB (62.4%)	+0.7 MB
Web builds	49.6 MB (15.4%)	6.5 MB (65.4%)	+0.7 MB

The slight .so increase (~0.7 MB per platform) is due to the rebuilt Intl extension now including additional symbols needed for MAIN_MODULE=2 compatibility.

Breakdown by variant

Build	Before	After	Saved	Reduction
Node Asyncify	241.6 MB	208.4 MB	33.2 MB	13.7%
Node JSPI	227.2 MB	193.8 MB	33.4 MB	14.7%
Web Asyncify	219.1 MB	191.7 MB	27.4 MB	12.5%
Web JSPI	200.3 MB	172.4 MB	28.0 MB	13.9%

JS glue code reduction

Build	Before	After	Saved	Reduction
Node Asyncify	~957 KB	~360 KB	~597 KB	62%
Node JSPI	~912 KB	~340 KB	~572 KB	63%
Web Asyncify	~735 KB	~263 KB	~472 KB	64%
Web JSPI	~716 KB	~236 KB	~480 KB	67%

---

Line Changes

PR	JS Glue Lines Before	JS Glue Lines After	Net
#3332 (JSPI)	422,100	146,463	-275,637
#3335 (Asyncify)	439,850	160,694	-279,156
Combined	861,950	307,157	-554,793

---

Performance Implications

MAIN_MODULE=2 tells Emscripten to only export symbols actually needed for dynamic linking, rather than exporting everything. This yields:

1. Smaller download size — 122 MB less across all builds means faster CI, faster clones, and faster deployments
2. Faster WebAssembly instantiation — Smaller .wasm files take less time to compile and instantiate in the browser (compilation cost is roughly proportional to binary size)
3. Lower memory usage — Fewer exported symbols means a smaller function table and less memory overhead at runtime
4. Smaller JS glue code — 63% smaller JS files means faster parsing and less memory for the JavaScript engine

Testing Instructions (or ideally a Blueprint)

CI

[brandonpayton]

@mho22, this looks good. Thank you!

How cool is this, especially for php-wasm/web download sizes?

[mho22]

@brandonpayton Well, not as light as Node builds but, still :

Now the entire PHP.wasm builds are dead code eliminated. 🎉

Size Reduction

Metric	Before	After	Saved
Total binary size	888 MB	766 MB	122 MB (13.7%)
.wasm files	680 MB	571 MB	109 MB (16%)
JS glue code	22.7 MB	8.2 MB	14.5 MB (63%)

Per-version .wasm reduction

PHP Version	Before (avg)	After (avg)	Reduction
7.4	~20 MB	~17 MB	17–19%
8.0	~21 MB	~17 MB	17–19%
8.1	~24 MB	~20 MB	15–17%
8.2	~25 MB	~21 MB	15–17%
8.3	~25 MB	~21 MB	15–17%
8.4	~27 MB	~23 MB	14–16%
8.5	~28 MB	~24 MB	14–15%

Web vs Node Build Comparison

Platform	Before	After	Saved	Reduction
Node builds	468.8 MB	402.2 MB	66.6 MB	14.2%
Web builds	419.4 MB	364.0 MB	55.4 MB	13.2%

Breakdown by file type

Platform	.wasm saved	JS glue saved	.so delta
Node builds	59.4 MB (16.5%)	8.0 MB (62.4%)	+0.7 MB
Web builds	49.6 MB (15.4%)	6.5 MB (65.4%)	+0.7 MB

The slight .so increase (~0.7 MB per platform) is due to the rebuilt Intl extension now including additional symbols needed for MAIN_MODULE=2 compatibility.

Breakdown by variant

Build	Before	After	Saved	Reduction
Node Asyncify	241.6 MB	208.4 MB	33.2 MB	13.7%
Node JSPI	227.2 MB	193.8 MB	33.4 MB	14.7%
Web Asyncify	219.1 MB	191.7 MB	27.4 MB	12.5%
Web JSPI	200.3 MB	172.4 MB	28.0 MB	13.9%

JS glue code reduction

Build	Before	After	Saved	Reduction
Node Asyncify	~957 KB	~360 KB	~597 KB	62%
Node JSPI	~912 KB	~340 KB	~572 KB	63%
Web Asyncify	~735 KB	~263 KB	~472 KB	64%
Web JSPI	~716 KB	~236 KB	~480 KB	67%

---

Line Changes

PR	JS Glue Lines Before	JS Glue Lines After	Net
#3332 (JSPI)	422,100	146,463	-275,637
#3335 (Asyncify)	439,850	160,694	-279,156
Combined	861,950	307,157	-554,793

---

Performance Implications

MAIN_MODULE=2 tells Emscripten to only export symbols actually needed for dynamic linking, rather than exporting everything. This yields:

1. Smaller download size — 122 MB less across all builds means faster CI, faster clones, and faster deployments
2. Faster WebAssembly instantiation — Smaller .wasm files take less time to compile and instantiate in the browser (compilation cost is roughly proportional to binary size)
3. Lower memory usage — Fewer exported symbols means a smaller function table and less memory overhead at runtime
4. Smaller JS glue code — 63% smaller JS files means faster parsing and less memory for the JavaScript engine

It would be interesting to benchmark the runtime impact, particularly WebAssembly instantiation time, time-to-first-PHP-response, and memory usage, to quantify the performance gains beyond file size.

[adamziel]

This is amazing ❤️ Thank you so much @mho22! @fellyph – let's highlight the smaller download sizes somewhere, could be with a few other recent updates.

[fellyph]

@adamziel I have posted about it https://make.wordpress.org/playground/2026/03/11/how-wordpress-playground-cut-php-wasm-binary-sizes-by-122-mb/

[brandonpayton]

@brandonpayton Well, not as light as Node builds but, still :
Now the entire PHP.wasm builds are dead code eliminated. 🎉

This is great, @mho22! Thank you!