A build_vector is the canonical representation rather than multiple
insert_vector_elts.
Unfortunately, this regresses quite a few tests now primarily due to not
having a vmv.s.x special case, but I hope we can improve this with future
patches.
Stress testing in our downstream found an infinite loop in DAG combine.
This patch breaks the infinite loop.
The insert_vector_element chain starts with a fixed vector undef.
Fixed vector undef is currently expanded to a build_vector of 0s
which gets lowered to a vmv.v.i. The insert chain overwrites all
elements so SimplifyDemandedVectorElts turns the vmv.v.i back into
undef and the cycle repeats.
We probably should custom lower fixed vector undef to scalable
vector undef. I think that would also fix the infinite loop, but
I didn't test that.
clang-format not found in user’s local PATH; not linting file.