Hello everyone,
I have recently randomly discovered the fact, that building with
`-march=ivybridge` does not necessarily produce the same output as
`-march=native` on an Intel Core i7 3770K (Ivy Bridge).
In particular, `-march=native` sets `-maes` whilst `-march=ivybridge`
does not.
After carefully considering the option that I'm in fact turning crazy
(e.g. I triple-checked that `-march=native` really does set
`-march=ivybridge` and `-mtune=ivybridge`), it seems like while this is
the case on the GCC version that I'm actively using (9.1.0), it is not
on a different machine (6.3.0 20170516 (Debian 6.3.0-18+deb9u1)).
Consider this method that yields a `test.s` file result:
$ touch test.cc
$ gcc -fverbose-asm -march=ivybridge test.cc -S
$ sed -i 1,/options\ enabled/d test.s
Given the 6.3.0 compiler, test.s contains `-maes`.
The 9.1.0 compiler's test.s does not contain `-maes`.
In fact, when you use the 9.1.0 compiler on the CPU mentioned before to
create `test1.s` with `-march=native` and `test2.s` with
`-march=ivybridge` as before, this is the only difference:
$ diff test1.s test.s
21c21
< # -m128bit-long-double -m64 -m80387 -maes -malign-stringops -mavx
---
> # -m128bit-long-double -m64 -m80387 -malign-stringops -mavx
I have run a git bisect starting with
4b5e15daff8b54440e3fda451c318ad31e532fab as the last known good commit and
12b43fabe5fc5aa7d6217a6736409e180d13db6e as the first known bad commit [1].
If I'm understanding the commit correctly, the change that causes this
is the removal of `PTA_AES` in
const wide_int_bitmask PTA_WESTMERE = PTA_NEHALEM | PTA_AES | PTA_PCLMUL;
as PTA_IVYBRIDGE contains PTA_SANDYBRIDGE which in turn contains
PTA_WESTMERE.
Is this an oversight or mistake?
Best regards,
Kevin Weidemann
References:
[1] git bisect result:
71c8e4e2f720bc7155ba2da7c0ee9136a9ab3283 is the first bad commit
commit 71c8e4e2f720bc7155ba2da7c0ee9136a9ab3283
Author: hjl <hjl@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Fri Feb 22 12:49:21 2019 +0000
x86: (Reapply) Move AESNI generation to Skylake and Goldmont
This is a repeat of commit r263989, which commit r264052 accidentally
reverted.
2019-02-22 Thiago Macieira <thiago.macie...@intel.com>
PR target/89444
* config/i386/i386.h (PTA_WESTMERE): Remove PTA_AES.
(PTA_SKYLAKE): Add PTA_AES.
(PTA_GOLDMONT): Likewise.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@269114
138bc75d-0d04-0410-961f-82ee72b054a4
:040000 040000 2c24ae2c6c6074acd52215a3340240989b3c1f6a
479b008acd81e383293abb23a69c9fa5da4afdc6 M gcc
bisect run success
