[AArch64] Use PerfectShuffle costs in AArch64TTIImpl::getShuffleCost

[dmgreen]

Summary

Given a shuffle with 4 elements size 16 or 32, we can use the costs directly from the PerfectShuffle tables to get a slightly more accurate cost for the resulting shuffle.

[samtebbs]

llvm/lib/Target/AArch64/AArch64PerfectShuffle.h

6590

Why do we have to limit this to 4x16 or 4x32 shuffles?

6602–6609

A comment about what is being done here would be beneficial.

6611–6617

A bit more elaboration here would be nice too.

[dmgreen]

llvm/lib/Target/AArch64/AArch64PerfectShuffle.h

6590

There is a comment in the summary of D123379 that might help explain perfect shuffles. The quick version is that they only support 4 entry shuffles, because otherwise the tables we store would just be too large.

6611–6617

I'm not sure exactly what else to say, other than this is how perfect shuffle tables work :)

[samtebbs]

LGTM!

llvm/lib/Target/AArch64/AArch64PerfectShuffle.h

6590

Ah thanks for the link, that explains it.

6611–6617

The comment in the post you linked did help a lot! cheers

[fhahn]

Just a heads up, I'm seeing a few 4-8% regressions on different AArch64 CPUs with this change for a few benchmarks. I still need to isolate the binary changes.

[dmgreen]

Did you ever manage to come up with a reproducer? I'm hope this new cost model is generally more accurate, but you know cost modelling.. The codegen might be off or their might be any number of second order effects going wrong. Let me know.

[fhahn]

In D123409#3496279, @dmgreen wrote:

Did you ever manage to come up with a reproducer? I'm hope this new cost model is generally more accurate, but you know cost modelling.. The codegen might be off or their might be any number of second order effects going wrong. Let me know.

The issue was that after this patch some code got vectorized when it wasn't profitable, but it looked like a general SLP issue. Previously it just didn't get vectorized because some ridiculously high costs where used for some shuffles. It looks like D115750 fixed the underlying issue and the code is back to not getting vectorized and original performance is restored :)

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

 
 bool AArch64TargetLowering::isShuffleMaskLegal(ArrayRef<int> M, EVT VT) const {
   // Currently no fixed length shuffles that require SVE are legal.
   if (useSVEForFixedLengthVectorVT(VT))
     return false;
 
   if (VT.getVectorNumElements() == 4 &&
       (VT.is128BitVector() || VT.is64BitVector())) {
-    unsigned PFIndexes[4];
-    for (unsigned i = 0; i != 4; ++i) {
-      if (M[i] < 0)
-        PFIndexes[i] = 8;
-      else
-        PFIndexes[i] = M[i];
-    }
-
-    // Compute the index in the perfect shuffle table.
-    unsigned PFTableIndex = PFIndexes[0] * 9 * 9 * 9 + PFIndexes[1] * 9 * 9 +
-                            PFIndexes[2] * 9 + PFIndexes[3];
-    unsigned PFEntry = PerfectShuffleTable[PFTableIndex];
-    unsigned Cost = (PFEntry >> 30);
-
-    // The cost tables encode cost 1 (or 0) shuffles using the value 0.
-    if (Cost == 0)
+    unsigned Cost = getPerfectShuffleCost(M);
+    if (Cost <= 1)
       return true;
   }
 
   bool DummyBool;
   int DummyInt;
   unsigned DummyUnsigned;
 
   return (ShuffleVectorSDNode::isSplatMask(&M[0], VT) || isREVMask(M, VT, 64) ||

llvm/lib/Target/AArch64/AArch64PerfectShuffle.h

 //===-- AArch64PerfectShuffle.h - AdvSIMD Perfect Shuffle Table -----------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file, which was autogenerated by llvm-PerfectShuffle, contains data
 // for the optimal way to build a perfect shuffle using AdvSIMD instructions.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIB_TARGET_AARCH64_AARCH64PERFECTSHUFFLE_H
 #define LLVM_LIB_TARGET_AARCH64_AARCH64PERFECTSHUFFLE_H
 
+#include "llvm/ADT/ArrayRef.h"
+
 // 31 entries have cost 0
 // 434 entries have cost 1
 // 2326 entries have cost 2
 // 3253 entries have cost 3
 // 517 entries have cost 4
 
 static const unsigned PerfectShuffleTable[6561 + 1] = {
     135053414U,  // <0,0,0,0>: Cost 1 vdup0 LHS

     835584U,     // <u,u,u,3>: Cost 0 copy LHS
     408620342U,  // <u,u,u,4>: Cost 1 vext1 LHS, RHS
     471087258U,  // <u,u,u,5>: Cost 1 vext2 LHS, RHS
     537753997U,  // <u,u,u,6>: Cost 1 vext3 LHS, RHS
     27705344U,   // <u,u,u,7>: Cost 0 copy RHS
     835584U,     // <u,u,u,u>: Cost 0 copy LHS
     0};
 
+static unsigned getPerfectShuffleCost(llvm::ArrayRef<int> M) {
+  assert(M.size() == 4 && "Expected a 4 entry perfect shuffle");
+
+  // Special case zero-cost nop copies, from either LHS or RHS.
+  if (llvm::all_of(llvm::enumerate(M), [](auto &E) {
+        return E.value() < 0 || E.value() == (int)E.index();
+      }))
+    return 0;
+  if (llvm::all_of(llvm::enumerate(M), [](auto &E) {
+        return E.value() < 0 || E.value() == (int)E.index() + 4;
+      }))
+    return 0;
+
+  // Get the four mask elementd from the 2 inputs. Perfect shuffles encode undef
+  // elements with value 8.
+  unsigned PFIndexes[4];
+  for (unsigned i = 0; i != 4; ++i) {
+    assert(M[i] < 8 && "Expected a maximum entry of 8 for shuffle mask");
+    if (M[i] < 0)
+      PFIndexes[i] = 8;
+    else
+      PFIndexes[i] = M[i];
+  }
+
+  // Compute the index in the perfect shuffle table.
+  unsigned PFTableIndex = PFIndexes[0] * 9 * 9 * 9 + PFIndexes[1] * 9 * 9 +
+                          PFIndexes[2] * 9 + PFIndexes[3];
+  unsigned PFEntry = PerfectShuffleTable[PFTableIndex];
+  // And extract the cost from the upper bits. The cost is encoded as Cost-1.
+  return (PFEntry >> 30) + 1;
+}
+
 #endif

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

 //===-- AArch64TargetTransformInfo.cpp - AArch64 specific TTI -------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "AArch64TargetTransformInfo.h"
 #include "AArch64ExpandImm.h"
+#include "AArch64PerfectShuffle.h"
 #include "MCTargetDesc/AArch64AddressingModes.h"
 #include "llvm/Analysis/IVDescriptors.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/CodeGen/BasicTTIImpl.h"
 #include "llvm/CodeGen/CostTable.h"
 #include "llvm/CodeGen/TargetLowering.h"
 #include "llvm/IR/Intrinsics.h"
InstructionCost AArch64TTIImpl::getSpliceCost(VectorType *Tp, int Index) {
   return LegalizationCost * LT.first;
 }
 
 InstructionCost AArch64TTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
                                                VectorType *Tp,
                                                ArrayRef<int> Mask, int Index,
                                                VectorType *SubTp,
                                                ArrayRef<Value *> Args) {
+  // If we have 4 elements for the shuffle and a Mask, get the cost straight
+  // from the perfect shuffle tables.
+  if (Mask.size() == 4 && Tp->getElementCount() == ElementCount::getFixed(4) &&
+      (Tp->getScalarSizeInBits() == 16 || Tp->getScalarSizeInBits() == 32) &&
+      all_of(Mask, [](int E) { return E < 8; }))
+    return getPerfectShuffleCost(Mask);
+
   Kind = improveShuffleKindFromMask(Kind, Mask);
   std::pair<InstructionCost, MVT> LT = TLI->getTypeLegalizationCost(DL, Tp);
   if (Kind == TTI::SK_Broadcast || Kind == TTI::SK_Transpose ||
       Kind == TTI::SK_Select || Kind == TTI::SK_PermuteSingleSrc ||
       Kind == TTI::SK_Reverse) {
     static const CostTblEntry ShuffleTbl[] = {
       // Broadcast shuffle kinds can be performed with 'dup'.
       { TTI::SK_Broadcast, MVT::v8i8,  1 },

llvm/test/Analysis/CostModel/AArch64/shuffle-other.ll

 ; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
 ; RUN: opt < %s -mtriple=aarch64--linux-gnu -passes='print<cost-model>' 2>&1 -disable-output | FileCheck %s
 
 define void @shuffle() {
 ; CHECK-LABEL: 'shuffle'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v7 = shufflevector <2 x i8> undef, <2 x i8> undef, <2 x i32> <i32 1, i32 0>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %v8 = shufflevector <4 x i8> undef, <4 x i8> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %v9 = shufflevector <8 x i8> undef, <8 x i8> undef, <8 x i32> <i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %v10 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v11 = shufflevector <2 x i16> undef, <2 x i16> undef, <2 x i32> <i32 1, i32 0>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %v12 = shufflevector <4 x i16> undef, <4 x i16> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v12 = shufflevector <4 x i16> undef, <4 x i16> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %v13 = shufflevector <8 x i16> undef, <8 x i16> undef, <8 x i32> <i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v14 = shufflevector <2 x i32> undef, <2 x i32> undef, <2 x i32> <i32 1, i32 0>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %v15 = shufflevector <4 x i32> undef, <4 x i32> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v15 = shufflevector <4 x i32> undef, <4 x i32> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16 = shufflevector <2 x float> undef, <2 x float> undef, <2 x i32> <i32 1, i32 0>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 3 for instruction: %v17 = shufflevector <4 x float> undef, <4 x float> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v17 = shufflevector <4 x float> undef, <4 x float> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
   %v7 = shufflevector <2 x i8> undef, <2 x i8> undef, <2 x i32> <i32 1, i32 0>
   %v8 = shufflevector <4 x i8> undef, <4 x i8> undef, <4 x i32> <i32 1, i32 3, i32 2, i32 0>
   %v9 = shufflevector <8 x i8> undef, <8 x i8> undef, <8 x i32> <i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1>
   %v10 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3, i32 0, i32 1>
 
   %v11 = shufflevector <2 x i16> undef, <2 x i16> undef, <2 x i32> <i32 1, i32 0>
;
   ret void
 }
 
 define void @concat() {
 ; CHECK-LABEL: 'concat'
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4i8 = shufflevector <2 x i8> undef, <2 x i8> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i8 = shufflevector <4 x i8> undef, <4 x i8> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i8 = shufflevector <8 x i8> undef, <8 x i8> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4i16 = shufflevector <2 x i16> undef, <2 x i16> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v4i16 = shufflevector <2 x i16> undef, <2 x i16> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i16 = shufflevector <4 x i16> undef, <4 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i16 = shufflevector <8 x i16> undef, <8 x i16> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4i32 = shufflevector <2 x i32> undef, <2 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v4i32 = shufflevector <2 x i32> undef, <2 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i32 = shufflevector <4 x i32> undef, <4 x i32> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4i64 = shufflevector <2 x i64> undef, <2 x i64> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 9 for instruction: %v4f16 = shufflevector <2 x half> undef, <2 x half> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v4f16 = shufflevector <2 x half> undef, <2 x half> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8f16 = shufflevector <4 x half> undef, <4 x half> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16f16 = shufflevector <8 x half> undef, <8 x half> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4f32 = shufflevector <2 x float> undef, <2 x float> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: %v4f32 = shufflevector <2 x float> undef, <2 x float> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8f32 = shufflevector <4 x float> undef, <4 x float> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4f64 = shufflevector <2 x double> undef, <2 x double> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 0 for instruction: ret void
 ;
   %v4i8 = shufflevector <2 x i8> undef, <2 x i8> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
   %v8i8 = shufflevector <4 x i8> undef, <4 x i8> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
   %v16i8 = shufflevector <8 x i8> undef, <8 x i8> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 

 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i8_2_2 = shufflevector <8 x i8> undef, <8 x i8> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 8, i32 9, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i8_2_3 = shufflevector <8 x i8> undef, <8 x i8> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 8, i32 9>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 9 for instruction: %v8i8_2_05 = shufflevector <8 x i8> undef, <8 x i8> undef, <8 x i32> <i32 0, i32 8, i32 9, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 90 for instruction: %v16i8_4_0 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 16, i32 17, i32 18, i32 19, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i8_4_1 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 16, i32 17, i32 18, i32 19, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i8_4_2 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 16, i32 17, i32 18, i32 19, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i8_4_3 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 16, i32 17, i32 18, i32 19>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 21 for instruction: %v16i8_4_05 = shufflevector <16 x i8> undef, <16 x i8> undef, <16 x i32> <i32 0, i32 1, i32 16, i32 17, i32 18, i32 19, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 18 for instruction: %v4i16_2_0 = shufflevector <4 x i16> undef, <4 x i16> undef, <4 x i32> <i32 0, i32 1, i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4i16_2_1 = shufflevector <4 x i16> undef, <4 x i16> undef, <4 x i32> <i32 4, i32 5, i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v4i16_2_0 = shufflevector <4 x i16> undef, <4 x i16> undef, <4 x i32> <i32 0, i32 1, i32 6, i32 7>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v4i16_2_1 = shufflevector <4 x i16> undef, <4 x i16> undef, <4 x i32> <i32 4, i32 5, i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 42 for instruction: %v8i16_2_0 = shufflevector <8 x i16> undef, <8 x i16> undef, <8 x i32> <i32 8, i32 9, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i16_2_1 = shufflevector <8 x i16> undef, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 8, i32 9, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i16_2_2 = shufflevector <8 x i16> undef, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 8, i32 9, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i16_2_3 = shufflevector <8 x i16> undef, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 8, i32 9>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 9 for instruction: %v8i16_2_05 = shufflevector <8 x i16> undef, <8 x i16> undef, <8 x i32> <i32 0, i32 8, i32 9, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 84 for instruction: %v16i16_4_0 = shufflevector <16 x i16> undef, <16 x i16> undef, <16 x i32> <i32 16, i32 17, i32 18, i32 19, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i16_4_1 = shufflevector <16 x i16> undef, <16 x i16> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 16, i32 17, i32 18, i32 19, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i16_4_2 = shufflevector <16 x i16> undef, <16 x i16> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 16, i32 17, i32 18, i32 19, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i16_4_3 = shufflevector <16 x i16> undef, <16 x i16> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 16, i32 17, i32 18, i32 19>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 21 for instruction: %v16i16_4_05 = shufflevector <16 x i16> undef, <16 x i16> undef, <16 x i32> <i32 0, i32 1, i32 16, i32 17, i32 18, i32 19, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v4i32_2_0 = shufflevector <4 x i32> undef, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 6, i32 7>
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v4i32_2_1 = shufflevector <4 x i32> undef, <4 x i32> undef, <4 x i32> <i32 4, i32 5, i32 0, i32 1>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %v4i32_2_1 = shufflevector <4 x i32> undef, <4 x i32> undef, <4 x i32> <i32 4, i32 5, i32 0, i32 1>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %v8i32_2_0 = shufflevector <8 x i32> undef, <8 x i32> undef, <8 x i32> <i32 8, i32 9, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i32_2_1 = shufflevector <8 x i32> undef, <8 x i32> undef, <8 x i32> <i32 0, i32 1, i32 8, i32 9, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i32_2_2 = shufflevector <8 x i32> undef, <8 x i32> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 8, i32 9, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v8i32_2_3 = shufflevector <8 x i32> undef, <8 x i32> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 8, i32 9>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 9 for instruction: %v8i32_2_05 = shufflevector <8 x i32> undef, <8 x i32> undef, <8 x i32> <i32 0, i32 8, i32 9, i32 3, i32 4, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 8 for instruction: %v16i32_4_0 = shufflevector <16 x i32> undef, <16 x i32> undef, <16 x i32> <i32 16, i32 17, i32 18, i32 19, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i32_4_1 = shufflevector <16 x i32> undef, <16 x i32> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 16, i32 17, i32 18, i32 19, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: %v16i32_4_2 = shufflevector <16 x i32> undef, <16 x i32> undef, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 16, i32 17, i32 18, i32 19, i32 12, i32 13, i32 14, i32 15>

llvm/test/Analysis/CostModel/AArch64/shuffle-select.ll

 ; CODE-LABEL: sel.v16i8
 ; CODE:       tbl v0.16b, { v0.16b, v1.16b }, v2.16b
 define <16 x i8> @sel.v16i8(<16 x i8> %v0, <16 x i8> %v1) {
   %tmp0 = shufflevector <16 x i8> %v0, <16 x i8> %v1, <16 x i32> <i32 0, i32 17, i32 2, i32 19, i32 4, i32 21, i32 6, i32 23, i32 8, i32 25, i32 10, i32 27, i32 12, i32 29, i32 14, i32 31>
   ret <16 x i8> %tmp0
 }
 
 ; COST-LABEL: sel.v4i16
-; COST:       Found an estimated cost of 18 for instruction: %tmp0 = shufflevector <4 x i16> %v0, <4 x i16> %v1, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
+; COST:       Found an estimated cost of 2 for instruction: %tmp0 = shufflevector <4 x i16> %v0, <4 x i16> %v1, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
 ; CODE-LABEL: sel.v4i16
 ; CODE:       rev32 v0.4h, v0.4h
 ; CODE:       trn2 v0.4h, v0.4h, v1.4h
 define <4 x i16> @sel.v4i16(<4 x i16> %v0, <4 x i16> %v1) {
   %tmp0 = shufflevector <4 x i16> %v0, <4 x i16> %v1, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
   ret <4 x i16> %tmp0
 }
 

llvm/test/Transforms/PhaseOrdering/AArch64/matrix-extract-insert.ll

 
 ; Function Attrs: argmemonly nofree nosync nounwind willreturn
 declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
 
 ; Function Attrs: nounwind ssp uwtable mustprogress
 
 define <4 x float> @reverse_hadd_v4f32(<4 x float> %a, <4 x float> %b) {
 ; CHECK-LABEL: @reverse_hadd_v4f32(
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x float> [[A:%.*]], <4 x float> undef, <2 x i32> <i32 2, i32 0>
-; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x float> [[A]], <4 x float> undef, <2 x i32> <i32 3, i32 1>
-; CHECK-NEXT:    [[TMP3:%.*]] = fadd <2 x float> [[TMP1]], [[TMP2]]
-; CHECK-NEXT:    [[TMP4:%.*]] = shufflevector <2 x float> [[TMP3]], <2 x float> poison, <4 x i32> <i32 undef, i32 undef, i32 0, i32 1>
-; CHECK-NEXT:    [[TMP5:%.*]] = shufflevector <4 x float> [[B:%.*]], <4 x float> undef, <2 x i32> <i32 2, i32 0>
-; CHECK-NEXT:    [[TMP6:%.*]] = shufflevector <4 x float> [[B]], <4 x float> undef, <2 x i32> <i32 3, i32 1>
-; CHECK-NEXT:    [[TMP7:%.*]] = fadd <2 x float> [[TMP5]], [[TMP6]]
-; CHECK-NEXT:    [[TMP8:%.*]] = shufflevector <2 x float> [[TMP7]], <2 x float> poison, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
-; CHECK-NEXT:    [[TMP9:%.*]] = shufflevector <4 x float> [[TMP8]], <4 x float> [[TMP4]], <4 x i32> <i32 0, i32 1, i32 6, i32 7>
-; CHECK-NEXT:    ret <4 x float> [[TMP9]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x float> [[B:%.*]], <4 x float> [[A:%.*]], <4 x i32> <i32 2, i32 0, i32 6, i32 4>
+; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x float> [[B]], <4 x float> [[A]], <4 x i32> <i32 3, i32 1, i32 7, i32 5>
+; CHECK-NEXT:    [[TMP3:%.*]] = fadd <4 x float> [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    ret <4 x float> [[TMP3]]
 ;
   %vecext = extractelement <4 x float> %a, i32 0
   %vecext1 = extractelement <4 x float> %a, i32 1
   %add = fadd float %vecext, %vecext1
   %vecinit = insertelement <4 x float> undef, float %add, i32 0
   %vecext2 = extractelement <4 x float> %a, i32 2
   %vecext3 = extractelement <4 x float> %a, i32 3
   %add4 = fadd float %vecext2, %vecext3