[llvm] [VectorCombine] Scalarize extracts of ZExt if profitable. (PR #142976)

[Florian Hahn via llvm-commits]

================
@@ -9,15 +9,25 @@ define void @zext_v4i8_all_lanes_used(<4 x i8> %src) {
 ; CHECK-LABEL: define void @zext_v4i8_all_lanes_used(
 ; CHECK-SAME: <4 x i8> [[SRC:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[TMP0:%.*]] = freeze <4 x i8> [[SRC]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast <4 x i8> [[TMP0]] to i32
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr i32 [[TMP1]], 24
+; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 255
+; CHECK-NEXT:    [[TMP4:%.*]] = lshr i32 [[TMP1]], 16
+; CHECK-NEXT:    [[TMP5:%.*]] = and i32 [[TMP4]], 255
+; CHECK-NEXT:    [[TMP6:%.*]] = lshr i32 [[TMP1]], 8
+; CHECK-NEXT:    [[TMP7:%.*]] = and i32 [[TMP6]], 255
+; CHECK-NEXT:    [[TMP8:%.*]] = lshr i32 [[TMP1]], 0
----------------
fhahn wrote:

Could add a special case, although I'm nto sure if that's the best way to go about it. It is probably better to just use InstSimplifyFolder to handle this generally: https://github.com/llvm/llvm-project/pull/146350

https://github.com/llvm/llvm-project/pull/142976