https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110946
Bug ID: 110946
Summary: 3x perf regression with -Os on M1 Pro
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
Assignee: unassigned at gcc dot gnu.org
Reporter: dave.rodgman at arm dot com
Target Milestone: ---
Please see
https://github.com/Mbed-TLS/mbedtls/pull/7784/commits/6cfd9b54ae0d06451c1a46a10e57fa099878bb03
for details.
On M1 Pro, under -Os, we see a 3.1x performance regression for AES-XTS, which
can be solved by forcing -O2 for two functions. For comparison, clang -Os gives
around 5% perf regression (which is more in the ballpark that I'd expect). So
it looks to me like gcc is getting something wrong when compiling these two
functions with -Os.
We measured a smaller but still significant difference (20-25%) on x86-64.
Affects all versions of gcc that I was able to test with (9 .. 12).
