LTO support View as Markdown

In fact, it does not seem to work very well.

Hi Go Kudo,

I read about the LTO feature from GCC in the past, and in my opinion,
LTO works have many years of improvement in the GCC, it works pretty
good nowadays. But programmers of Open Source projects were really
clever the last twenty years. I read about bench tests where larger
projects changes from normal compiling to -lto in GCC and after large
benchmarking, they do not have much performance benefits from LTO. They
said in these reports that mostly the bottleneck which -lto solves, were
not existing in these projects: Developers for example move critical
codes in the past from the .c-files into the .h-headers, so GCC can
inline them without having such a feature like -lto. Or there use parts
of "single-file" approaches for projects in C which have same compiling
results as with the feature -lto.

So, I think LTO works fine now, but you need projects which have these
kind of bottlenecks to benefit from LTO. :)

Best regards,
Thomas

ps:
Sorry, for two e-mails, Go, I was not able to press the right answer
button in my email program. ^^

Am 12.03.2022 19:17 schrieb Go Kudo:

At present, PHP cannot be built using LTO (Link Time Optimization).

LTO is a compiler feature that can improve performance by optimizing at
link time.
Chromium is also using this feature.

https://gcc.gnu.org/onlinedocs/gccint/LTO-Overview.html

The reason for the LTO failure appears to be the Zend Engine's use of
GCC's
global register variables. Conversely, it is otherwise compatible with
LTO.
(except: opcache).

I modified toolchain too to enable and validate LTOs outside of Zend
Engine
and OPcache:

https://github.com/zeriyoshi/php-src/commit/b25c237837fec2f82d268d8dbd45ec886baf474f

I tested the following compilation options:

gcc: (Debian 10.2.1-6) 10.2.1 20210110
CFLAGS="-fstack-protector-strong -fpic -fpie -O3 -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1 -pie"
$ ./sapi/cli/php ./Zend/bench.php
simple             0.010
simplecall         0.005
simpleucall        0.010
simpleudcall       0.013
mandel             0.052
mandel2            0.049
ackermann(7)       0.012
ary(50000)         0.003
ary2(50000)        0.002
ary3(2000)         0.020
fibo(30)           0.035
hash1(50000)       0.004
hash2(500)         0.004
heapsort(20000)    0.012
matrix(20)         0.012
nestedloop(12)     0.010
sieve(30)          0.006
strcat(200000)     0.002
------------------------
Total              0.261

vs

gcc: (Debian 10.2.1-6) 10.2.1 20210110
CFLAGS="-fstack-protector-strong -fpic -fpie -O3 -flto 
-fuse-linker-plugin
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1 -pie -flto -fuse-linker-plugin"
$ ./sapi/cli/php ./Zend/bench.php
simple             0.006
simplecall         0.003
simpleucall        0.010
simpleudcall       0.014
mandel             0.050
mandel2            0.049
ackermann(7)       0.012
ary(50000)         0.003
ary2(50000)        0.002
ary3(2000)         0.020
fibo(30)           0.035
hash1(50000)       0.004
hash2(500)         0.004
heapsort(20000)    0.012
matrix(20)         0.011
nestedloop(12)     0.010
sieve(30)          0.007
strcat(200000)     0.002
------------------------
Total              0.255

In fact, it does not seem to work very well. However, it may be
effective
when large numbers of extensions are built into PHP.

Is anyone interested in supporting this?