https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107675
Bug ID: 107675
Summary: [13 Regression] GCC-13 is significantly slower to
startup on C++ programs
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
Target Milestone: ---
Target: aarch64*
The following simple testcase:
#include <cstdio>
int main(int argc, char** argv) {
printf("Hello world\n");
return 0;
}
is on average twice as slow as GCC 12 during startup:
> perf diff perf.data.gcc.12 perf.data.gcc.13
# Event 'cycles'
#
# Baseline Delta Abs Shared Object Symbol
# ........ ......... ................ ...............................
#
100.00% +42.66% gcc-13.exe [.] fde_single_encoding_compare
Looking at perf the entirety of of the difference is spent in __libc_start_main
which on GCC 13 calls __libc_csu_init which calls init_object.constprop.0.
This constprop function spends half the time in frame_heapsort and the other
half in fde_single_encoding_compare. Together these two calls are responsible
for the 2x slower startup.
Is it possible to mitigate this? At startup it's currently executing more than
6.5x the number of instructions as GCC-12 which is quite noticeable on small
devices.
