https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62077
--- Comment #6 from Sven C. Dack <sven.c.dack at virginmedia dot com> --- It seems the problem is caused by the use of the jobserver. Changing bootstrap-lto.mk from: ... STAGE2_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1 -ffat-lto-objects ... to: ... STAGE2_CFLAGS += -flto=1 -flto-partition=none -frandom-seed=1 -ffat-lto-objects STAGE3_CFLAGS += -flto=1 -flto-partition=none -frandom-seed=1 -ffat-lto-objects ... Results in a success without using an additional compare script: ... Comparing stages 2 and 3 warning: gcc/cc1obj-checksum.o differs warning: gcc/cc1-checksum.o differs warning: gcc/cc1plus-checksum.o differs Comparison successful. ...