Improve windows performance (php-src side)

[henderkes]

Describe your feature request

Php on windows is currently leaving a good 30%+ performance on the table by compiling with MSVC instead of Clang (preserve_none Tailcall VM). Contact php internals team and if they don't want to switch, recompile only php8ts.dll and php8embed.liv with Clang.

[henderkes]

Problem: the GL compiled dependencies make Clang fail when using Ltcg. The PGO profile is also only for msvc. The configure script also doesn't even perform the preserve_none check, but that was a quick fix.

Given the lack of ltcg and pgo, clang builds are actually ~30% slower in my testing, ~50% slower with call VM. It's probably not realistic to get Microsoft to change compiler for all the 40 dependencies, so this may be a dead end. Not giving up quite yet, but also don't have many ideas left.

[henderkes]

New approach, support for __preserve_none with msvc where possible. Will be a bit more extensive rework. Clang is essentially out of the question :/

[henderkes]

Msvc isn't stable enough with tail recursion, the majority of [[msvc::musttail]] fail with error C4737: Unable to perform required tail call. Performance may be degraded.. Not forcing tail recursion isn't an option either, because the opline handlers obviously blow the call stack.

I suppose I could attempt to switch the call VM to __preserve_none instead of using the tail call vm. Would likely help some register spilling, but I wouldn't expect huge gains.

[henderkes]

preserve_none over fastcall for CALL VM handlers and func handler = ~8% performance uplift.

However, something weird is going on there

configure --disable-all --enable-cli --enable-embed --enable-zts --enable-bcmath --enable-calendar --enable-ctype --enable-filter --with-iconv --with-libxml --with-mysqlnd --enable-phar --with-readline --enable-session --enable-tokenizer --enable-xmlreader --enable-zlib --with-curl --enable-intl --with-openssl --enable-pdo --with-pdo-sqlite --with-sqlite3 --enable-zip

^ the --disable-all improves performance by ~30%.

[henderkes]

It's --enable-security-flags (default enabled). What a bummer, that's a massive amount of performance.

Edit: specifically, it's only the /GUARD:CF. Together with the calling convention switch, we're looking at +40% performance if we could get that disabled. Probably not, though.

[henderkes]

php/php-src#21563

[henderkes]

I managed to get JIT working when /guard:cf is disabled:

# official 8.5.4
❯❯ ~  18:22 wrk -c20 -t4 -d15s http://localhost/en/
Running 15s test @ http://localhost/en/
  4 threads and 20 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   115.59ms  111.58ms 814.41ms   88.03%
    Req/Sec    59.05     26.35   111.00     66.67%
  3318 requests in 15.02s, 4.49MB read
Requests/sec:    220.86
Transfer/sec:    305.90KB
❯❯ ~  18:23 frankenphp stop && Start-Process -NoNewWindow -FilePath "frankenphp" -ArgumentList "php-server --root public"
# current 8.6.0-dev with __preserve_none
❯❯ ~  18:23 wrk -c20 -t4 -d15s http://localhost/en/
Running 15s test @ http://localhost/en/
  4 threads and 20 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    62.23ms   16.05ms 257.80ms   90.11%
    Req/Sec    81.24     14.09   110.00     75.42%
  4843 requests in 15.02s, 6.58MB read
Requests/sec:    322.49
Transfer/sec:    448.71KB

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