[llvm-dev] Does specifying -O2 affect *0.0.preopt.bc when LDFLAGS=" -flto -fuse-ld=gold -Wl, -plugin-opt=save-temps "?

[Tim Northover via llvm-dev]

On Sun, 20 Jan 2019 at 17:28, Peng Yu via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> For the final executable myprog, I got the following files. But the
> original make toolchain may specify options like -O2. In this case, is
> myprog.0.0.preopt.bc still the same as if -O2 were not specified? Or
> myprog.0.0.preopt.bc would not be the same whether -O2 is specified or
> not.

Clang generates slightly different code based on the optimization
level. It attaches specific attributes to each function generated for
certain levels:

-Oz --> "minsize"
-Os --> "optsize"
-O0 --> "optnone" (this is also the default).

At -O, -O1, -O2 and -O3 no attribute gets attached. They're just
handled by configuring LLVM slightly differently while running its
passes.

There may be other differences, but if so I'm not aware of them.
Another question more suited for cfe-dev really.

Cheers.

Tim.