[llvm] [PowerPC] Optimize BUILD_VECTOR from load and zeros (PR #73609)

[Nemanja Ivanovic via llvm-commits]

================
@@ -3437,6 +3437,12 @@ def : Pat<(store (i32 (extractelt v4i32:$A, 1)), ForceXForm:$src),
 def : Pat<(store (f32 (extractelt v4f32:$A, 1)), ForceXForm:$src),
           (STIWX (EXTRACT_SUBREG $A, sub_64), ForceXForm:$src)>;
 
+// BUILD_VECTOR via loads and zeros.
+def : Pat<(v2f64 (build_vector (f64 (extloadf32 ForceXForm:$src)), (f64 fpimm0))),
----------------
nemanjai wrote:

Do we not have an opportunity to also improve the following:
- Non-extending load
- Single precision and i32 (other elements are zeros)
- Zero is at a different index
- Little endian

https://github.com/llvm/llvm-project/pull/73609