1 //===- RegAllocScore.cpp - evaluate regalloc policy quality ---------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 /// Calculate a measure of the register allocation policy quality. This is used
9 /// to construct a reward for the training of the ML-driven allocation policy.
10 /// Currently, the score is the sum of the machine basic block frequency-weighed
11 /// number of loads, stores, copies, and remat instructions, each factored with
12 /// a relative weight.
13 //===----------------------------------------------------------------------===//
14 
15 #include "RegAllocScore.h"
16 #include "llvm/ADT/ilist_iterator.h"
17 #include "llvm/CodeGen/MachineBasicBlock.h"
18 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
19 #include "llvm/CodeGen/MachineFunction.h"
20 #include "llvm/CodeGen/MachineInstr.h"
21 #include "llvm/CodeGen/MachineInstrBundleIterator.h"
22 #include "llvm/CodeGen/TargetInstrInfo.h"
23 #include "llvm/CodeGen/TargetSubtargetInfo.h"
24 #include "llvm/MC/MCInstrDesc.h"
25 #include "llvm/Support/CommandLine.h"
26 
27 using namespace llvm;
28 cl::opt<double> CopyWeight("regalloc-copy-weight", cl::init(0.2), cl::Hidden);
29 cl::opt<double> LoadWeight("regalloc-load-weight", cl::init(4.0), cl::Hidden);
30 cl::opt<double> StoreWeight("regalloc-store-weight", cl::init(1.0), cl::Hidden);
31 cl::opt<double> CheapRematWeight("regalloc-cheap-remat-weight", cl::init(0.2),
32                                  cl::Hidden);
33 cl::opt<double> ExpensiveRematWeight("regalloc-expensive-remat-weight",
34                                      cl::init(1.0), cl::Hidden);
35 #define DEBUG_TYPE "regalloc-score"
36 
37 RegAllocScore &RegAllocScore::operator+=(const RegAllocScore &Other) {
38   CopyCounts += Other.copyCounts();
39   LoadCounts += Other.loadCounts();
40   StoreCounts += Other.storeCounts();
41   LoadStoreCounts += Other.loadStoreCounts();
42   CheapRematCounts += Other.cheapRematCounts();
43   ExpensiveRematCounts += Other.expensiveRematCounts();
44   return *this;
45 }
46 
47 bool RegAllocScore::operator==(const RegAllocScore &Other) const {
48   return copyCounts() == Other.copyCounts() &&
49          loadCounts() == Other.loadCounts() &&
50          storeCounts() == Other.storeCounts() &&
51          loadStoreCounts() == Other.loadStoreCounts() &&
52          cheapRematCounts() == Other.cheapRematCounts() &&
53          expensiveRematCounts() == Other.expensiveRematCounts();
54 }
55 
56 bool RegAllocScore::operator!=(const RegAllocScore &Other) const {
57   return !(*this == Other);
58 }
59 
60 double RegAllocScore::getScore() const {
61   double Ret = 0.0;
62   Ret += CopyWeight * copyCounts();
63   Ret += LoadWeight * loadCounts();
64   Ret += StoreWeight * storeCounts();
65   Ret += (LoadWeight + StoreWeight) * loadStoreCounts();
66   Ret += CheapRematWeight * cheapRematCounts();
67   Ret += ExpensiveRematWeight * expensiveRematCounts();
68 
69   return Ret;
70 }
71 
72 RegAllocScore
73 llvm::calculateRegAllocScore(const MachineFunction &MF,
74                              const MachineBlockFrequencyInfo &MBFI) {
75   return calculateRegAllocScore(
76       MF,
77       [&](const MachineBasicBlock &MBB) {
78         return MBFI.getBlockFreqRelativeToEntryBlock(&MBB);
79       },
80       [&](const MachineInstr &MI) {
81         return MF.getSubtarget().getInstrInfo()->isTriviallyReMaterializable(
82             MI);
83       });
84 }
85 
86 RegAllocScore llvm::calculateRegAllocScore(
87     const MachineFunction &MF,
88     llvm::function_ref<double(const MachineBasicBlock &)> GetBBFreq,
89     llvm::function_ref<bool(const MachineInstr &)>
90         IsTriviallyRematerializable) {
91   RegAllocScore Total;
92 
93   for (const MachineBasicBlock &MBB : MF) {
94     double BlockFreqRelativeToEntrypoint = GetBBFreq(MBB);
95     RegAllocScore MBBScore;
96 
97     for (const MachineInstr &MI : MBB) {
98       if (MI.isDebugInstr() || MI.isKill() || MI.isInlineAsm()) {
99         continue;
100       }
101       if (MI.isCopy()) {
102         MBBScore.onCopy(BlockFreqRelativeToEntrypoint);
103       } else if (IsTriviallyRematerializable(MI)) {
104         if (MI.getDesc().isAsCheapAsAMove()) {
105           MBBScore.onCheapRemat(BlockFreqRelativeToEntrypoint);
106         } else {
107           MBBScore.onExpensiveRemat(BlockFreqRelativeToEntrypoint);
108         }
109       } else if (MI.mayLoad() && MI.mayStore()) {
110         MBBScore.onLoadStore(BlockFreqRelativeToEntrypoint);
111       } else if (MI.mayLoad()) {
112         MBBScore.onLoad(BlockFreqRelativeToEntrypoint);
113       } else if (MI.mayStore()) {
114         MBBScore.onStore(BlockFreqRelativeToEntrypoint);
115       }
116     }
117     Total += MBBScore;
118   }
119   return Total;
120 }
121