[X86][AVX] Match broadcast loads through a bitcast

AVX1 v8i32/v4i64 shuffles are bitcasted to v8f32/v4f64, this patch peeks through any bitcast to check for a load node to allow broadcasts to occur.

This is a re-commit of r257055 after r257264 fixed 32-bit broadcast loads of i64 scalars.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257266 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed