[llvm] [VPlan] Implement interleaving as VPlan-to-VPlan transform. (PR #95842)

[via llvm-commits]

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@@ -143,15 +143,17 @@ define void @test_induction_step_needs_expansion(ptr noalias %j, ptr %k, i64 %l,
 ; CHECK:       vector.ph:
 ; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[L]], 64
 ; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[L]], [[N_MOD_VF]]
+; CHECK-NEXT:    [[DOTSPLATINSERT2:%.*]] = insertelement <16 x i16> poison, i16 [[TMP0]], i64 0
+; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <16 x i16> [[DOTSPLATINSERT2]], <16 x i16> poison, <16 x i32> zeroinitializer
+; CHECK-NEXT:    [[DOTSPLAT3:%.*]] = mul <16 x i16> <i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16>, [[TMP2]]
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ayalz wrote:

Mul by a vector of 16's after broadcast, versus mul by single scalar 16 before broadcast.

https://github.com/llvm/llvm-project/pull/95842