[LLVMdev] Thoughts about the llvm architecture

[Jochen Wilhelmy]

Hi!

The following thoughts about the llvm architecture I'd like to share 
with you
(from the perspective of a user):

- If a backend has no vector support, then I wonder why there is no 
de-vectorization
pass that operates on indermediate llvm-ir. I would think that if you 
use such a target
then you have to insert a target independent pass before it that it does 
not have to
care about vector code. The advantage is that constant vector components 
can already
be handled by instcombine. what do you think?

- If the integer width of a backend is smaller than the integers in the 
llvm-ir (e.g.
an 8 bit microcontroller) then i also would expect a target independent 
integer
splitting. the difficulty here is how to handle carry in the ir. but the 
advantage would
be that if i have e.g. int32_t a = 5 then three of the four bytes are 
zero and can
be optimized by instcombine. I have seen very bad code in the output of 
avr-gcc in this case.

-Jochen