> > But then why is the mode QImode in the first place? The access is > definitely of SImode. >
that's in the test case: s->arr[0] = 0x12345678; it is QImode from that in expand_assignment: to_rtx = expand_expr (tem, NULL_RTX, VOIDmode, EXPAND_WRITE); tem is "s", a MEM_REF, of QImode, perfectly aligned. the mode is only OK to access *s or s->pad. It is wrong for s->srr[0]. in store_bit_field the mode is used in store_fixed_bit_field: mode = GET_MODE (op0); if (GET_MODE_BITSIZE (mode) == 0 || GET_MODE_BITSIZE (mode)> GET_MODE_BITSIZE (word_mode)) mode = word_mode; mode = get_best_mode (bitsize, bitnum, bitregion_start, bitregion_end, MEM_ALIGN (op0), mode, MEM_VOLATILE_P (op0)); if (mode == VOIDmode) goto boom; so this restricts the possible access mode. word_mode, means no restriction. Everything would be OK if MEM_ALIGN(op0) was byte-aligned, but we have a problem if MEM_ALIGN(op0)>=WORD_MODE. Do you understand? Bernd.
