Reduce library size

[vitaut]

Need to revisit library size optimizations (https://www.zverovich.net/2020/05/21/reducing-library-size.html) since there was a bit of a regression compared to 7.0:

% clang++ -std=c++17  -I include -O2 -DNDEBUG test.cc src/format.cc
% strip a.out
% ls -l a.out
-rwxr-xr-x  1 viz  staff  193960 May 20 11:50 a.out

For comparison 7.0 generates

-rwxr-xr-x  1 viz  staff  127472 May 20 11:53 a.out

with the latest clang and libc++. Looks like some of the regression is due to newer clang and standard library.

[vitaut]

7.1 is ~20k bigger because of adding Dragonbox (0c8ffe9). Maybe we can reuse powers of 10 table between Grisu and Dragonbox.

[vitaut]

Most of the regression happened between 7.1.0 and 7.1.1 so should be easy to track down.

[vitaut]

The regression between 7.1.0 and 7.1.1 was to preserve ABI compatibility (4081b2f) and is fixed now.

[vitaut]

~30k regression was caused by b268f88.

[sergiud]

Following #2293, I would suggest enabling -fvisibility=hidden and -fvisibility-inlines-hidden by default in CMakeLists.txt:

set (CMAKE_CXX_VISIBILITY_PRESET hidden)
set (CMAKE_VISIBILITY_INLINES_HIDDEN ON)

$ du -h build-before/libfmt.so.7.1.4
244K
$ du -h build-after/libfmt.so.7.1.4
212K

I can provide a PR.

[vitaut]

I would suggest enabling -fvisibility=hidden and -fvisibility-inlines-hidden by default

Good idea but I would suggest using target properties instead of global CMake flags.

I can provide a PR.

Please do.

[vitaut]

With b268f88 regression fixed:

% clang++ -std=c++17  -I include -O2 -DNDEBUG test.cc src/format.cc && strip a.out && ls -l a.out
-rwxr-xr-x  1 viz  staff  161168 May 21 06:27 a.out

[sergiud]

CMake target properties would not provide any benefit here. On contrary, users will not be able to override the default choice by passing CMAKE_CXX_VISIBILITY_PRESET and CMAKE_VISIBILITY_INLINES_HIDDEN as cache variables.

[vitaut]

OK, just make sure that it works well with fmt used as a subproject, i.e. something like

fmt/CMakeLists.txt

Line 60 in 18af1dc

if (FMT_MASTER_PROJECT AND NOT CMAKE_BUILD_TYPE)

[vitaut]

The remaining two ~15k regressions (each):

• a457e16
• eef4ba9

[alexezeder]

Brag time 😉

Some of the regressions can be found here - https://alexezeder.github.io/fmt_bnchmrk/
There are the results generated by fmt_bnchmrk_gnrtr with fmt_bnchmrk for {fmt}.
But I don't want to make any promises about the website (aka Pages) because it's running on Raspberry Pi, and if it dies, then there won't be any updates for the website. But the code will be available, I hope, forever.

[vitaut]

This is amazing, thanks for putting it together.

[vitaut]

After 5a2b88f:

% clang++ -std=c++17 -I include -O2 -DNDEBUG test.cc src/format.cc && strip a.out && ls -l a.out
-rwxr-xr-x  1 viz  staff  143632 May 30 06:17 a.out

[vitaut]

This is slightly smaller than 7.1.0 so I think it's good enough and we could look at floating point separately.

[vitaut]

Here are results with LTO and -Os:

% clang++ -std=c++17 -I include -Os -flto -DNDEBUG test.cc src/format.cc && strip a.out && ls -l a.out
-rwxr-xr-x  1 viz  staff  101776 May 30 06:23 a.out