https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92999
--- Comment #1 from Jim Rees <jimreesma at gmail dot com> --- Reproduced on gcc-9.2 and figured out a fix, though I'm not savvy enough with this code to say it's a complete fix. In (gcc-9.2.0 release) gcc/config/arm/arm.c: 6226a6227 > int ag_mode_size; 6241c6242,6243 < shift = GET_MODE_SIZE(ag_mode) / GET_MODE_SIZE(SFmode); --- > ag_mode_size = MAX (GET_MODE_SIZE (ag_mode), GET_MODE_SIZE (SFmode)); > shift = ag_mode_size / GET_MODE_SIZE(SFmode); Prior to the patch, shift becomes 0 when ag_mode is HFmode, which is what causes every field of the struct to get mapped to the same floating-point register.
