Comment 0 for bug 1667407

Dear Maintainer,

The sha256sum provided by coreutils (without openssl) is performing
poorly with gcc versions >= 4.9 until 7.0 (currently under development).
The reason for that is the -fschedule-insns optimization that is used
with -O2. By simply deactivating it, there is a performance improvement
of 2 to 3 times.

I'm using Ubuntu 16.10 and the coreutils package version 8.25-2ubuntu2.

Please check the following closed debian bug report:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=854053

Be aware of the following conditions that are required:
* If ppc64le
* If gcc being used is >= 4.9 and < 7.0

Notes:
1) gcc-7 is not affected by this bug (verified on 20170129 snapshot).
2) clang is not affected by this bug (verified on v3.8 and v3.9).
3) strangely the sha512 is not affected by this.

Below a demonstration of how it performs on my POWER8 machine:

===================================================
$ (./configure && make -j9) > /dev/null && time src/sha256sum ~/ubuntu-16.10-server-ppc64el.iso
configure: WARNING: libacl development library was not found or not usable.
configure: WARNING: GNU coreutils will be built without ACL support.
configure: WARNING: libattr development library was not found or not usable.
configure: WARNING: GNU coreutils will be built without xattr support.
configure: WARNING: libcap library was not found or not usable.
configure: WARNING: GNU coreutils will be built without capability support.
configure: WARNING: libgmp development library was not found or not usable.
configure: WARNING: GNU coreutils will be built without GMP support.
src/who.c: In function 'print_user':
src/who.c:454:20: warning: initialization discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
         int *a = utmp_ent->ut_addr_v6;
                    ^~~~~~~~
d14bdb413ea6cdc8d9354fcbc37a834b7de0c23f992deb0c6764d0fd5d65408e /home/gut/ubuntu-16.10-server-ppc64el.iso

real 0m18.670s
user 0m16.566s
sys 0m0.745s

$ # now with the following patch: ## Check Michael Stone's patch for an improved version.
$ diff Makefile.in ../Makefile.in
8989c8989
< @am__fastdepCC_TRUE@ $(COMPILE) -MT $@ -MD -MP -MF $$depbase.Tpo -c -o $@ $< &&\
---
> @am__fastdepCC_TRUE@ $(COMPILE) $$([ "$@" == "lib/sha256.o" ] && echo "-fno-schedule-insns") -MT $@ -MD -MP -MF $$depbase.Tpo -c -o $@ $< &&\
$ cp ../Makefile.in Makefile.in
$ (./configure && make -j9) > /dev/null && time src/sha256sum ~/ubuntu-16.10-server-ppc64el.iso
configure: WARNING: libacl development library was not found or not usable.
configure: WARNING: GNU coreutils will be built without ACL support.
configure: WARNING: libattr development library was not found or not usable.
configure: WARNING: GNU coreutils will be built without xattr support.
configure: WARNING: libcap library was not found or not usable.
configure: WARNING: GNU coreutils will be built without capability support.
configure: WARNING: libgmp development library was not found or not usable.
configure: WARNING: GNU coreutils will be built without GMP support.
src/who.c: In function 'print_user':
src/who.c:454:20: warning: initialization discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
         int *a = utmp_ent->ut_addr_v6;
                    ^~~~~~~~
d14bdb413ea6cdc8d9354fcbc37a834b7de0c23f992deb0c6764d0fd5d65408e /home/gut/ubuntu-16.10-server-ppc64el.iso

real 0m5.903s
user 0m5.560s
sys 0m0.255s