[llvm] [SLP]Fix graph traversal in getSpillCost (PR #124984)

[Alexey Bataev via llvm-commits]

================
@@ -149,37 +149,27 @@ define <4 x float> @exp_4x(ptr %a) {
 ; CHECK-SAME: (ptr [[A:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP0:%.*]] = load <4 x float>, ptr [[A]], align 16
-; CHECK-NEXT:    [[VECEXT:%.*]] = extractelement <4 x float> [[TMP0]], i32 0
-; CHECK-NEXT:    [[TMP1:%.*]] = tail call fast float @expf(float [[VECEXT]])
-; CHECK-NEXT:    [[VECINS:%.*]] = insertelement <4 x float> undef, float [[TMP1]], i32 0
-; CHECK-NEXT:    [[VECEXT_1:%.*]] = extractelement <4 x float> [[TMP0]], i32 1
-; CHECK-NEXT:    [[TMP2:%.*]] = tail call fast float @expf(float [[VECEXT_1]])
-; CHECK-NEXT:    [[VECINS_1:%.*]] = insertelement <4 x float> [[VECINS]], float [[TMP2]], i32 1
-; CHECK-NEXT:    [[VECEXT_2:%.*]] = extractelement <4 x float> [[TMP0]], i32 2
-; CHECK-NEXT:    [[TMP3:%.*]] = tail call fast float @expf(float [[VECEXT_2]])
-; CHECK-NEXT:    [[VECINS_2:%.*]] = insertelement <4 x float> [[VECINS_1]], float [[TMP3]], i32 2
-; CHECK-NEXT:    [[VECEXT_3:%.*]] = extractelement <4 x float> [[TMP0]], i32 3
-; CHECK-NEXT:    [[TMP4:%.*]] = tail call fast float @expf(float [[VECEXT_3]])
-; CHECK-NEXT:    [[VECINS_3:%.*]] = insertelement <4 x float> [[VECINS_2]], float [[TMP4]], i32 3
-; CHECK-NEXT:    ret <4 x float> [[VECINS_3]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x float> [[TMP0]], <4 x float> poison, <2 x i32> <i32 0, i32 1>
----------------
alexey-bataev wrote:

It is not related to comment above, the cost of sclararized vector calls misses spill cost. I can add this extra cost, it will avoid the vectorization. But generally speaking, such nodes should not be vectorized at all, should be marked as buildvector nodes

https://github.com/llvm/llvm-project/pull/124984