enabling LTO by default is vastly inappropriate (was Re: Bug#1015386: dietlibc: ftbfs with LTO (link time optimization) enabled)

[Thorsten Glaser <tg@debian.org>]

Matthias Klose dixit:

>The goal is to enable this optimization by default in an upcoming
>Debian release in dpkg-buildflags for 64bit architectures.  The goal
>is to get this package to build with link time optimizations, or to
>explicitly disable link time optimizations for this package build.

This is daring, especially from the GCC maintainer.

GCC (both in Debian and upstream) have been ignoring many known
bugs related to LTO (both in the -fwhole-program --combine and
the -flto form) which I found due to mksh’s testsuite and reported
for *years*.

These bugs are subtile miscompilations. In mksh, only one test
by accident fails due to the GCC LTO bug. It’s definitely *not*
ripe for general use, *especially* not on software without a
large testsuite with large coverage.

(As for dietlibc, it’s inappropriate there anyway, so it opts out.)

Uploaded,
//mirabilos
-- 
„Cool, /usr/share/doc/mksh/examples/uhr.gz ist ja ein Grund,
mksh auf jedem System zu installieren.“
	-- XTaran auf der OpenRheinRuhr, ganz begeistert
(EN: “[…]uhr.gz is a reason to install mksh on every system.”)