[llvm] [LV] Improve cost model for some replicating recipes (PR #192056)

[Florian Hahn via llvm-commits]

================
@@ -380,22 +380,70 @@ exit:
 define void @sdiv_power_of_2_divisor_in_replicate_region(i32 %x, ptr %dst, i64 %n) {
 ; CHECK-LABEL: define void @sdiv_power_of_2_divisor_in_replicate_region(
 ; CHECK-SAME: i32 [[X:%.*]], ptr [[DST:%.*]], i64 [[N:%.*]]) {
-; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:  [[ENTRY:.*:]]
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp sgt i64 [[N]], 0
 ; CHECK-NEXT:    [[C_2:%.*]] = icmp slt i64 [[N]], 9
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[C_1]])
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[C_2]])
 ; CHECK-NEXT:    br label %[[LOOP:.*]]
 ; CHECK:       [[LOOP]]:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[N_RND_UP:%.*]] = add i64 [[N]], 3
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[N_RND_UP]], 4
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[N_RND_UP]], [[N_MOD_VF]]
+; CHECK-NEXT:    [[TRIP_COUNT_MINUS_1:%.*]] = sub i64 [[N]], 1
+; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[TRIP_COUNT_MINUS_1]], i64 0
+; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x i64> [[BROADCAST_SPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK:       [[VECTOR_BODY]]:
----------------
fhahn wrote:

It's not obvious to me that his change here is profitable? AFAICT there is no benefit from vectorization (everything is secularized), but we introduce extra overhead compared to the scalar loop by predication

https://github.com/llvm/llvm-project/pull/192056