[PATCH] D79818: [lld] Support size levels with (Thin)LTO

Wed May 13 17:29:42 PDT 2020

MaskRay added a comment.

In D79818#2035448 <https://reviews.llvm.org/D79818#2035448>, @pcc wrote:

> In D79818#2035301 <https://reviews.llvm.org/D79818#2035301>, @phosek wrote:
>
> > In D79818#2035232 <https://reviews.llvm.org/D79818#2035232>, @MaskRay wrote:
> >
> > > @mehdi_amini @pcc @tejohnson
> > >
> > > I just saw another issue saying that `clang -Os -flto=thin a.c` does not work https://bugs.llvm.org/show_bug.cgi?id=45913 (+ @manojgupta)
> > >  I marked it as yet another duplicate of PR42445
> > >
> > > For -Os, clang driver passes -plugin-opt=Os (https://github.com/llvm/llvm-project/blob/master/clang/lib/Driver/ToolChains/CommonArgs.cpp#L402) but neither LLVMgold.so nor LLD recognizes `-plugin-opt=Os`. 
> > >  -Oz is similar. What is the concrete suggestion here? For quick reference, the `-plugin-opt=O` logic was added by rL256146 <https://reviews.llvm.org/rL256146>.
> >
> >
> > The issue form my perspective is the inconsistency. Today, lld accepts `-plugin-opt=O<number>` but it doesn't accept `-plugin-opt=O<letter>`, but Clang automatically translates `-O<anything>` to `-plugin-opt=O<anything>` which results in a failure when your try to use `-Os`, `-Oz` or `-Og` with (Thin)LTO.
>
>
> This is where the bug is then. The clang driver should be translating these arguments to `-plugin-opt O2`.

Thanks. Preparing a patch to address -Os -Oz -Og -O.

Repository:
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https://reviews.llvm.org/D79818