[llvm] [X86] lowerBuildVectorToBitOp - build_vector(trunc(x),trunc(y),...) -> trunc(build_vector(x,y,...)) (PR #88945)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@topperc This is what I was working on when the build_pair issue arose - the setcc-wide-types.ll tests in particular use wide integer types as part of an is_all_zero test, which end up as a huge tree of:

`build_vector(build_pair(build_pair(), build_pair()), build_pair(build_pair(), build_pair()))`

https://github.com/llvm/llvm-project/pull/88945