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Re: [PATCH v2 3/6] configure: add option to enable LTO

From: Daniel P . Berrangé
Subject: Re: [PATCH v2 3/6] configure: add option to enable LTO
Date: Mon, 26 Oct 2020 15:50:06 +0000
User-agent: Mutt/1.14.6 (2020-07-11)

On Mon, Oct 26, 2020 at 10:51:43AM +0100, Paolo Bonzini wrote:
> On 23/10/20 22:06, Daniele Buono wrote:
> > This patch allows to compile QEMU with link-time optimization (LTO).
> > Compilation with LTO is handled directly by meson. This patch adds checks
> > in configure to make sure the toolchain supports LTO.
> > 
> > Currently, allow LTO only with clang, since I have found a couple of issues
> > with gcc-based LTO.
> > 
> > In case fuzzing is enabled, automatically switch to llvm's linker (lld).
> > The standard bfd linker has a bug where function wrapping (used by the fuzz*
> > targets) is used in conjunction with LTO.
> > 
> > Tested with all major versions of clang from 6 to 12
> > 
> > Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
> What are the problems like if you have GCC or you ar/linker are not up
> to the job?  I wouldn't mind omitting the tests since this has to be
> enabled explicitly by the user.

We temporarily disabled LTO in Fedora rawhide due to GCC bugs causing
wierd test suite asserts. Those were pre-release versions of GCC/binutils
though. I've just tested again and LTO works correctly, so I've enabled
LTO once again. 

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