[Bug target/100340] Bootstrap fails with Clang 12.0.5 (XCode 12.5)

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100340

--- Comment #7 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Iain Sandoe from comment #6)
> (In reply to Richard Biener from comment #5)
> > Does it work when you use STAGE1_CFLAGS="-O0" (I think clang defaults to
> > optimizing?).  To rule out compare-debug issues also try
> > --without-build-config

> I am discussing with OSS folks at Apple whether this is an intentional
> change (i.e to produce better optimised code) or an accidental one.

If the result comes back "we intended to do this" then there are a couple of
options.

1) ask them to implement some option to disable this (and we can trigger that
option from -gtoggle)  Which would mean that the production compiler had the
advantage of the additional optimisation - but we could still prove that our
code-gen was the same with/without debug.

2) We can implement (1) ourselves using the llas driver I wrote - which drives
the LLVM backend, but presents command line options like cctools (i.e. more
like GAS).

for now I guess we have to wait for a reply,