https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62173
--- Comment #36 from Jiong Wang <jiwang at gcc dot gnu.org> --- and for rtl level improvement, need to enable DF_DU_CHAIN build on top of existing DF_UD_CHAIN (may cause extra compile time resource consumption). one draft patch is here, no feedback yet. https://gcc.gnu.org/ml/gcc-patches/2015-02/msg00736.html as both tree and rtl fix contain generic code modifications, I think it's better to defer it to next stage-1 given the issue itself is enhancement not bug.
