Re: [PATCH] configure: Add --enable-lto

[Richard Henderson]

On 12/4/22 11:40, Peter Maydell wrote:
> On Sun, 4 Dec 2022 at 00:04, Richard Henderson
> <richard.henderson@linaro.org> wrote:
> > Separately control b_lto without --enable-cfi.
> > Also add --disable-lto for completeness.
>
> Before this patch, CFI defaults to false and therefore LTO
> also defaults to false. After this patch, LTO defaults to
> true even if CFI is false. Intentional change ?

Nope.  Oops.

> Do we have figures for whether LTO produces an interesting
> performance improvement ?

No idea.  I wrote this after finding a bug report in which someone tried to add -flto via 
--extra-cflags.

> We should probably complain if the user tries '--enable-cfi --disable-lto'
> rather than silently doing something that presumably doesn't work.

We do, in meson.build:

if get_option('cfi')
  cfi_flags=[]
  # Check for dependency on LTO
  if not get_option('b_lto')
    error('Selected Control-Flow Integrity but LTO is disabled')


r~