[AArch64] Reduce vector insert/extract cost for Kryo

[mssimpso]

Summary

Kryo can perform vector inserts and extracts very efficiently. This patch lowers the default insert/extract cost for Kryo from 3 to 2. Some performance results are given below (positive difference are performance improvements).

Benchmark              Diff (%) 
-------------------    --------
spec2000/eon               1.74
spec2000/gcc               1.17
spec2000/mesa              0.97
spec2000/vortex            0.26
spec2006/dealII            0.76
spec2006/gcc               0.07
spec2006/h264ref           1.63
spec2006/libquantum        2.88
spec2006/milc              0.25
spec2006/namd             -0.17
spec2006/soplex            1.43

[mcrosier]

LGTM. Thanks, Matt.

lib/Target/AArch64/AArch64TargetTransformInfo.cpp

if (Index != -1U) {
     Index = Index % Width;
 
     // The element at index zero is already inside the vector.
     if (Index == 0)
       return 0;
   }
 
   // All other insert/extracts cost this much.
+  if (ST->isKryo())
+    return 2;
   return 3;
 }
 
 int AArch64TTIImpl::getArithmeticInstrCost(
     unsigned Opcode, Type *Ty, TTI::OperandValueKind Opd1Info,
     TTI::OperandValueKind Opd2Info, TTI::OperandValueProperties Opd1PropInfo,
     TTI::OperandValueProperties Opd2PropInfo) {
   // Legalize the type.

test/Analysis/CostModel/AArch64/kryo.ll

+; RUN: opt < %s -cost-model -analyze -mcpu=kryo | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64--linux-gnu"
+
+; CHECK-LABEL: vectorInstrCost
+define void @vectorInstrCost() {
+
+    ; Vector extracts - extracting the first element should have a zero cost;
+    ; all other elements should have a cost of two.
+    ;
+    ; CHECK: cost of 0 {{.*}} extractelement <2 x i64> undef, i32 0
+    ; CHECK: cost of 2 {{.*}} extractelement <2 x i64> undef, i32 1
+    %t1 = extractelement <2 x i64> undef, i32 0
+    %t2 = extractelement <2 x i64> undef, i32 1
+
+    ; Vector inserts - inserting the first element should have a zero cost; all
+    ; other elements should have a cost of two.
+    ;
+    ; CHECK: cost of 0 {{.*}} insertelement <2 x i64> undef, i64 undef, i32 0
+    ; CHECK: cost of 2 {{.*}} insertelement <2 x i64> undef, i64 undef, i32 1
+    %t3 = insertelement <2 x i64> undef, i64 undef, i32 0
+    %t4 = insertelement <2 x i64> undef, i64 undef, i32 1
+
+    ret void
+}