LLVM Clang Compiler Optimization Benchmarks From -O0 To -O3 -march=native

[duby229]

I know what the flag does. The "package manager"'s debug mode removes -fomit-frame-pointer and adds -g, resulting in enough debug info when I need it. Easy enough to trigger a rebuild in such occasions.

What distro are you using? This package manager sounds interesting just based on what little you've said.

[chithanh]

t would've been nice if you threw in the -Ofast flag which you've been known to be using.

Using -Ofast will turn on optimizations which violate the C/C++ standard and may produce incorrect code. So when including in a benchmark the generated code needs to be checked for that, or it needs to be pointed out explicitly.

[howarth]

Comparing the optimization levels between gcc and clang is also greatly complicated by the fact that clang also vectorizes at -O1, -O2 and -Os whereas gcc only does that for -O3.

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

http://llvm.org/releases/3.7.0/docs/Vectorizers.html

[Krejzi]

What distro are you using? This package manager sounds interesting just based on what little you've said.

It's my own, based on Linux From Scratch. The "package manager" is just a bash script, which installs files to a destdir and generates a tarball and a small, install scriptlet to install the package to the system.

https://github.com/elkrejzi/system-management/blob/master/buildscripts/master.sh

[Krejzi]

Using -Ofast will turn on optimizations which violate the C/C++ standard and may produce incorrect code. So when including in a benchmark the generated code needs to be checked for that, or it needs to be pointed out explicitly.

Yes, I am aware of that. Some packages even complained about using -Ofast (it pulls -ffast-math), such as PostgreSQL, SQLite, Glibc, and so on. But so far, I haven't noticed any visible issues. One of Michael's GCC benchmarks showed -Ofast was a bit ahead of others.

[unquaid]

How about optimization with -fprofile-use ? http://clang.llvm.org/docs/UsersManu...d-optimization
The compiler must choose the best way to optimize each function!