[Bug gold/21062] Building GCC in LTO mode fails when using ld.gold on AARCH64

[tulipawn at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=21062

--- Comment #4 from PeteVine <tulipawn at gmail dot com> ---
OK, so I've managed to identify the root cause of this bug, namely, the
-mfix-cortex-a53-843419 erratum workaround, which happens via the linker.

To recap, ld.gold produces crashing code if both LTO and
-mfix-cortex-a53-843419 are used at the same time. Removing the workaround
switch or using ld.bfd allows to bootstrap GCC using LTO
(--with-build-config=bootstrap-lto).

So, a compiler built with --enable-fix-cortex-a53-843419 needs just
-mcpu/mtune=cortex-a53 to trigger the workaround. 

In my tests, it made code produced that way slower on a currently available
revision of A53, which is not mentioned in the documentation. Otherwise I would
have found out if it was still necessary a long time ago :)

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