On Fri, Nov 15, 2013 at 2:24 PM, Bernd Edlinger <bernd.edlin...@hotmail.de> wrote: >> >> 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].
I undestand that, but why isn't that immediately adjusted to use TYPE_MODE (TREE_TYPE (to))? The above expands *s, not s->arr[0]. Using the mode of *s if it is not equal to that of the destination doesn't make any sense (usually it will be BLKmode anyway). This seems to be the source of multiple problems. > 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.
