[Bug middle-end/78994] New: -Ofast makes aarch64 C++ benchmark slower

[tulipawn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78994

            Bug ID: 78994
           Summary: -Ofast makes aarch64 C++ benchmark slower
           Product: gcc
           Version: 5.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tulipawn at gmail dot com
  Target Milestone: ---

Created attachment 40463
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40463&action=edit
Preprocessed source + assembly files

After make && ./build/dsp-bench, the results look as follows

@ -O3 -mcpu=cortex-a53 -ftree-vectorize

iir:    67945 ns per loop
iir_2:  67952 ns per loop

@ -Ofast -mcpu=cortex-a53 -ftree-vectorize

iir:    73367 ns per loop
iir_2:  73349 ns per loop