[llvm] [SLP][REVEC] Fix ShuffleVector does not consider alternate instruction. (PR #134599)

[Han-Kuan Chen via llvm-commits]

================
@@ -1,14 +1,28 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -passes=slp-vectorizer,instcombine -S -slp-revec -slp-max-reg-size=1024 -slp-threshold=-100 %s | FileCheck %s
+; RUN: opt -passes=slp-vectorizer -S -slp-revec -slp-max-reg-size=1024 -slp-threshold=-100 %s | FileCheck %s
+; RUN: opt -passes=slp-vectorizer,instcombine -S -slp-revec -slp-max-reg-size=1024 -slp-threshold=-100 %s | FileCheck %s --check-prefix COMBINE
 
 define void @test1(ptr %in, ptr %out) {
 ; CHECK-LABEL: @test1(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = load <8 x i32>, ptr [[IN:%.*]], align 1
-; CHECK-NEXT:    [[TMP1:%.*]] = zext <8 x i32> [[TMP0]] to <8 x i64>
-; CHECK-NEXT:    store <8 x i64> [[TMP1]], ptr [[OUT:%.*]], align 8
+; CHECK-NEXT:    [[OUT:%.*]] = getelementptr inbounds i64, ptr [[OUT1:%.*]], i64 0
+; CHECK-NEXT:    [[TMP2:%.*]] = call <16 x i32> @llvm.vector.insert.v16i32.v8i32(<16 x i32> poison, <8 x i32> [[TMP0]], i64 0)
+; CHECK-NEXT:    [[TMP3:%.*]] = shufflevector <16 x i32> [[TMP2]], <16 x i32> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
----------------
HanKuanChen wrote:

We need to gather %0 since %1 and %2 use it. It is <16 x i32> eventually.
```
3.
Operand 0:
    %0 = load <8 x i32>, ptr %in, align 1
    %0 = load <8 x i32>, ptr %in, align 1
Operand 1:
  <8 x i32> poison
  <8 x i32> poison
Scalars:
    %6 = shufflevector <8 x i32> %0, <8 x i32> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
    %5 = shufflevector <8 x i32> %0, <8 x i32> poison, <4 x i32> <i32 4, i32 5, i32 6, i32 7>
State: Vectorize
MainOp:   %6 = shufflevector <8 x i32> %0, <8 x i32> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
AltOp:   %6 = shufflevector <8 x i32> %0, <8 x i32> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
VectorizedValue: NULL
ReuseShuffleIndices: Empty
ReorderIndices:
UserTreeIndex: {User:2 EdgeIdx:0}

4.
Scalars:
    %0 = load <8 x i32>, ptr %in, align 1
    %0 = load <8 x i32>, ptr %in, align 1
State: NeedToGather
MainOp:   %0 = load <8 x i32>, ptr %in, align 1
AltOp:   %0 = load <8 x i32>, ptr %in, align 1
VectorizedValue: NULL
ReuseShuffleIndices: Empty
ReorderIndices:
UserTreeIndex: {User:3 EdgeIdx:0}
```

https://github.com/llvm/llvm-project/pull/134599