[llvm] [LV] Remove common extends and selects in CSE (PR #147731)

[Sam Tebbs via llvm-commits]

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@@ -1295,8 +1295,7 @@ define i32 @predicated_not_dominates_reduction_twoadd(ptr nocapture noundef read
 ; CHECK-NEXT:    [[TMP5:%.*]] = zext nneg <4 x i8> [[TMP4]] to <4 x i32>
 ; CHECK-NEXT:    [[TMP7:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP5]])
 ; CHECK-NEXT:    [[TMP8:%.*]] = add i32 [[TMP7]], [[VEC_PHI]]
-; CHECK-NEXT:    [[TMP9:%.*]] = zext nneg <4 x i8> [[TMP4]] to <4 x i32>
-; CHECK-NEXT:    [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP9]])
+; CHECK-NEXT:    [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP5]])
----------------
SamTebbs33 wrote:

Without removing selects, the diff looks like this:
```
 ; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[INDEX]] to i64
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[H:%.*]], i64 [[TMP0]]
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i8>, ptr [[TMP1]], align 1
+; CHECK-NEXT:    [[DOTNOT:%.*]] = icmp eq <4 x i8> [[WIDE_LOAD]], zeroinitializer
 ; CHECK-NEXT:    [[TMP2:%.*]] = udiv <4 x i8> [[WIDE_LOAD]], splat (i8 31)
 ; CHECK-NEXT:    [[TMP3:%.*]] = shl nuw nsw <4 x i8> [[TMP2]], splat (i8 3)
 ; CHECK-NEXT:    [[TMP4:%.*]] = udiv <4 x i8> [[TMP3]], splat (i8 31)
 ; CHECK-NEXT:    [[TMP5:%.*]] = zext nneg <4 x i8> [[TMP4]] to <4 x i32>
-; CHECK-NEXT:    [[TMP7:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP5]])
+; CHECK-NEXT:    [[TMP6:%.*]] = select <4 x i1> [[DOTNOT]], <4 x i32> zeroinitializer, <4 x i32> [[TMP5]]
+; CHECK-NEXT:    [[TMP7:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP6]])
 ; CHECK-NEXT:    [[TMP8:%.*]] = add i32 [[TMP7]], [[VEC_PHI]]
-; CHECK-NEXT:    [[TMP9:%.*]] = zext nneg <4 x i8> [[TMP4]] to <4 x i32>
+; CHECK-NEXT:    [[TMP9:%.*]] = select <4 x i1> [[DOTNOT]], <4 x i32> zeroinitializer, <4 x i32> [[TMP5]]
 ; CHECK-NEXT:    [[TMP10:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[TMP9]])
 ; CHECK-NEXT:    [[TMP11]] = add i32 [[TMP10]], [[TMP8]]
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4
```
which is a lot worse.

https://github.com/llvm/llvm-project/pull/147731