Disappeared flag: -maes on -march=ivybridge, present in -march=native

[Kevin Weidemann]

On Monday, 29 July 2019, Marc Glisse wrote:
>> This is a repeat of commit r263989, which commit r264052 
>> accidentally reverted.
> (...) As you can see, this is very much on purpose. See 
> https://gcc.gnu.org/ml/gcc-patches/2018-08/msg01940.html for the 
> explanation that came with the patch.

D'oh! I shouldn't have investigated this in the middle of the night,
apparently. I grepped the history for `r263989`, but the commit doesn't
contain that string, but instead
> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263989
(so without the `r` prefix). I didn't find the commit so I discarded the
idea of trying to find it way too quickly. Especially given the fact, 
that the repeated commit was found by the bisect and not the original 
one, I randomly decided to stop looking for it. Should've investigated 
this further after starting the day clear-headed!

On Monday, 29 July 2019 07:47 CEST Thiago Macieira wrote:
> Older versions of GCC turned AES on for -march=westmere and up, but 
> not anymore. The commit you found changed that.
Ok, gotcha! I didn't know that not all machines with those platforms
have AES.

> if you ran GCC [...] you'd get a fully working build for your CPU 
> using all CPU features you can use.
> 
> That's different from LLVM, which attempts to find which CPU most 
> closely matches yours. In that VM scenario, it would either disable 
> some features you could use or enable ones you can't.

Thanks for the interesting pointers, and both of your answers!

--
Kevin Weidemann