[DAGCombiner] Add support for scalarising extracts of a vector setcc (#116031)

For IR like this:

  %icmp = icmp ult <4 x i32> %a, splat (i32 5)
  %res = extractelement <4 x i1> %icmp, i32 1

where there is only one use of %icmp we can take a similar approach
to what we already do for binary ops such add, sub, etc. and convert
this into

  %ext = extractelement <4 x i32> %a, i32 1
  %res = icmp ult i32 %ext, 5

For AArch64 targets at least the scalar boolean result will almost
certainly need to be in a GPR anyway, since it will probably be
used by branches for control flow. I've tried to reuse existing code
in scalarizeExtractedBinop to also work for setcc.

NOTE: The optimisations don't apply for tests such as
extract_icmp_v4i32_splat_rhs in the file

CodeGen/AArch64/extract-vector-cmp.ll

because scalarizeExtractedBinOp only works if one of the input
operands is a constant.

0 files changed, 0 insertions, 0 deletions