On Thu, Aug 9, 2018 at 2:24 PM Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> wrote: > > I must say that I'm struggling a bit lately with the simplification > of bitfield accesses and I'm more and more inclined to add bitfield > insert & bit field extract instruction. It would help a lot but it > would also force to duplicate or redo a lot of the simplifications > already done for ASR/LSR/SH/AND/OR. I would really suggest against it. Turning bitfields into just plain memory accesses and shift-and-mask operations as quickly as possible is almost certainly the right thing to do. gcc special-cases bitfields way too much, and it has caused some very nasty issues. See for example my ancient bug-report at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48696 which is also a strong argument for the whole "keep the base type around, and do *not* think of it as just bits X-Y access", because it turns out that the base type matters for both access size and for access rules (ie volatile). Now, I'm assuming you were thinking of just an "arithmetic" insert/extract model (so separate from the memory access), and while that at least avoids the access issues, I can pretty much guarantee that it just makes for even more special cases and combinations than just turning them into shift-and-mask operations. Linus
