https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123972
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- Another surprising thing might be that VIEW_CONVERT_EXPR can be int<->float "conversion" as well and for vectors before vector lowering such can be tree_nop_conversion_p because the vector mode might be BLKmode for both. Likewise a vector short <-> vector int conversion can appear as nop conversion iff both vector modes are BLKmode.
