[llvm] [SLP][REVEC] Make SLP vectorize shufflevector. (PR #102489)

[Han-Kuan Chen via llvm-commits]

================
@@ -10116,6 +10212,13 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
       // TODO: Check the reverse order too.
       return VecCost;
     };
+    if (SLPReVec && !E->isAltShuffle())
+      return GetCostDiff(GetScalarCost, [](InstructionCost) {
+        // shufflevector will be eliminated by instcombine because the
+        // shufflevector masks are used in order (guaranteed by
+        // getShufflevectorNumGroups). The vector cost is 0.
----------------
HanKuanChen wrote:

The first test?
```
; 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:    ret void
;
```
shufflevector is eliminated.

https://github.com/llvm/llvm-project/pull/102489