[llvm] [GlobalISel] Refactor extractParts() (PR #75223)

[via llvm-commits]

================
@@ -460,12 +460,14 @@ body:             |
     ; CHECK-NEXT: [[EVEC3:%[0-9]+]]:_(s32) = G_EXTRACT_VECTOR_ELT [[SHUF]](<4 x s32>), [[C3]](s64)
     ; CHECK-NEXT: [[EVEC4:%[0-9]+]]:_(s32) = G_EXTRACT_VECTOR_ELT [[SHUF1]](<4 x s32>), [[C]](s64)
     ; CHECK-NEXT: [[EVEC5:%[0-9]+]]:_(s32) = G_EXTRACT_VECTOR_ELT [[SHUF1]](<4 x s32>), [[C1]](s64)
-    ; CHECK-NEXT: [[BUILD_VECTOR2:%[0-9]+]]:_(<4 x s32>) = G_BUILD_VECTOR [[EVEC]](s32), [[EVEC1]](s32), [[EVEC2]](s32), [[EVEC3]](s32)
-    ; CHECK-NEXT: [[BUILD_VECTOR3:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[EVEC4]](s32), [[EVEC5]](s32)
-    ; CHECK-NEXT: G_STORE [[BUILD_VECTOR2]](<4 x s32>), [[COPY8]](p0) :: (store (<4 x s32>), align 32)
+    ; CHECK-NEXT: [[BUILD_VECTOR2:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[EVEC]](s32), [[EVEC1]](s32)
+    ; CHECK-NEXT: [[BUILD_VECTOR3:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[EVEC2]](s32), [[EVEC3]](s32)
+    ; CHECK-NEXT: [[BUILD_VECTOR4:%[0-9]+]]:_(<2 x s32>) = G_BUILD_VECTOR [[EVEC4]](s32), [[EVEC5]](s32)
+    ; CHECK-NEXT: [[CONCAT_VECTORS:%[0-9]+]]:_(<4 x s32>) = G_CONCAT_VECTORS [[BUILD_VECTOR2]](<2 x s32>), [[BUILD_VECTOR3]](<2 x s32>)
+    ; CHECK-NEXT: G_STORE [[CONCAT_VECTORS]](<4 x s32>), [[COPY8]](p0) :: (store (<4 x s32>), align 32)
----------------
chuongg3 wrote:

@davemgreen and I have been looking at this, to see if there is anywhere where it might cause problems. It looks like it can come up in some cases, but it usually limited to odd sized vectors. It looks like it would be a good optimization to add - I will add it to the list of things to do

https://github.com/llvm/llvm-project/pull/75223