[llvm] r251904 - [X86] Generate .cfi_adjust_cfa_offset correctly when pushing arguments

[Reid Kleckner via llvm-commits]

I agree with Rafael, but it's a bit of a policy change for LLVM. For
example, I don't think we currently describe our epilogues with CFI.

On Tue, Nov 3, 2015 at 8:08 AM, Rafael Espíndola <
llvm-commits at lists.llvm.org> wrote:

> On 3 November 2015 at 10:55, Kuperstein, Michael M
> <michael.m.kuperstein at intel.com> wrote:
> > GCC is always precise, but that seems unnecessary when we only care
> about performing unwinding for synchronous EH (since in this case, we only
> need to be right at call sites), and inflates the module size.
> >
> > It's actually a bit hard to compare apples-to-apples here, since for
> -O2, there's no definitely harm in emitting extra CFI, but clang doesn't
> use pushes, and for -Os, GCC defaults to -no-omit-frame-pointer, so the
> issue does not arise.
>
> -Os -fomit-frame-pointers?
>
> I think it is incorrect to say that we don't care about asynchronous
> unwinding (not exceptions). The .eh_frame is part of the ABI and any
> tool wanting to unwind can depend on it being precise.
>
> Cheers,
> Rafael
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