https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61929
--- Comment #4 from Charles Greathouse <gcc at crg4 dot com> --- I now have a testcase for failure with -floop-parallelize-all (without -fcheck-data-deps). I believe this is the same bug, or at least related, because this testcase also fails with the previous compile command. int main() {} void generateICE2(char *s, int i) { for (; i >= 2; i--) s[i] = s[i-1]; } This fails with gcc testcase.c -lm -O2 -floop-parallelize-all -floop-nest-optimize or even gcc testcase.c -lm -O2 -floop-parallelize-all -floop-nest-optimize -fno-aggressive-loop-optimizations -fno-align-functions -fno-align-jumps -fno-align-labels -fno-align-loops -fno-asynchronous-unwind-tables -fno-branch-count-reg -fno-caller-saves -fno-combine-stack-adjustments -fno-common -fno-compare-elim -fno-cprop-registers -fno-crossjumping -fno-cse-follow-jumps -fno-dce -fno-defer-pop -fno-delete-null-pointer-checks -fno-devirtualize -fno-dse -fno-early-inlining -fno-expensive-optimizations -fno-forward-propagate -fno-gcse -fno-gcse-lm -fno-guess-branch-probability -fno-hoist-adjacent-loads -fno-if-conversion -fno-if-conversion2 -fno-inline -fno-inline-atomics -fno-inline-functions-called-once -fno-inline-small-functions -fno-ipa-cp -fno-ipa-profile -fno-ipa-pure-const -fno-ipa-reference -fno-ipa-sra -fno-ira-hoist-pressure -fno-ivopts -fno-jump-tables -fno-math-errno -fno-merge-constants -fno-move-loop-invariants -fno-optimize-register-move -fno-optimize-sibling-calls -fno-optimize-strlen -fno-peephole -fno-peephole2 -fno-prefetch-loop-arrays -fno-regmove -fno-rename-registers -fno-reorder-blocks -fno-reorder-functions -fno-rerun-cse-after-loop -fno-sched-critical-path-heuristic -fno-sched-dep-count-heuristic -fno-sched-group-heuristic -fno-sched-interblock -fno-sched-last-insn-heuristic -fno-sched-rank-heuristic -fno-sched-spec -fno-sched-spec-insn-heuristic -fno-sched-stalled-insns-dep -fno-schedule-insns2 -fno-set-stack-executable -fno-short-enums -fno-shrink-wrap -fno-signed-zeros -fno-split-ivs-in-unroller -fno-split-wide-types -fno-strict-aliasing -fno-thread-jumps -fno-trapping-math -fno-tree-bit-ccp -fno-toplevel-reorder -fno-tree-builtin-call-dce -fno-tree-ccp -fno-tree-coalesce-vars -fno-tree-copy-prop -fno-tree-copyrename -fno-tree-cselim -fno-tree-dce -fno-tree-dominator-opts -fno-tree-dse -fno-tree-forwprop -fno-tree-fre -fno-tree-loop-if-convert -fno-tree-loop-im -fno-tree-loop-ivcanon -fno-tree-phiprop -fno-tree-pre -fno-tree-pta -fno-tree-reassoc -fno-tree-scev-cprop -fno-tree-sink -fno-tree-slp-vectorize -fno-tree-slsr -fno-tree-sra -fno-tree-switch-conversion -fno-tree-tail-merge -fno-tree-ter -fno-tree-vect-loop-version -fno-tree-vrp -fno-unit-at-a-time -fno-var-tracking -fno-var-tracking-assignments -fno-web which is -O2 with everything but floop-parallelize-all -floop-nest-optimize -ftree-loop-optimize -ftree-ch -fthreadsafe-statics turned off. However the bug does not appear at -O1 and below even with these options.