LLVM  13.0.0git
SIInsertHardClauses.cpp
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1 //===- SIInsertHardClauses.cpp - Insert Hard Clauses ----------------------===//
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 //
9 /// \file
10 /// Insert s_clause instructions to form hard clauses.
11 ///
12 /// Clausing load instructions can give cache coherency benefits. Before gfx10,
13 /// the hardware automatically detected "soft clauses", which were sequences of
14 /// memory instructions of the same type. In gfx10 this detection was removed,
15 /// and the s_clause instruction was introduced to explicitly mark "hard
16 /// clauses".
17 ///
18 /// It's the scheduler's job to form the clauses by putting similar memory
19 /// instructions next to each other. Our job is just to insert an s_clause
20 /// instruction to mark the start of each clause.
21 ///
22 /// Note that hard clauses are very similar to, but logically distinct from, the
23 /// groups of instructions that have to be restartable when XNACK is enabled.
24 /// The rules are slightly different in each case. For example an s_nop
25 /// instruction breaks a restartable group, but can appear in the middle of a
26 /// hard clause. (Before gfx10 there wasn't a distinction, and both were called
27 /// "soft clauses" or just "clauses".)
28 ///
29 /// The SIFormMemoryClauses pass and GCNHazardRecognizer deal with restartable
30 /// groups, not hard clauses.
31 //
32 //===----------------------------------------------------------------------===//
33 
34 #include "AMDGPU.h"
35 #include "GCNSubtarget.h"
37 #include "llvm/ADT/SmallVector.h"
38 
39 using namespace llvm;
40 
41 #define DEBUG_TYPE "si-insert-hard-clauses"
42 
43 namespace {
44 
45 enum HardClauseType {
46  // Texture, buffer, global or scratch memory instructions.
47  HARDCLAUSE_VMEM,
48  // Flat (not global or scratch) memory instructions.
49  HARDCLAUSE_FLAT,
50  // Instructions that access LDS.
51  HARDCLAUSE_LDS,
52  // Scalar memory instructions.
53  HARDCLAUSE_SMEM,
54  // VALU instructions.
55  HARDCLAUSE_VALU,
56  LAST_REAL_HARDCLAUSE_TYPE = HARDCLAUSE_VALU,
57 
58  // Internal instructions, which are allowed in the middle of a hard clause,
59  // except for s_waitcnt.
60  HARDCLAUSE_INTERNAL,
61  // Instructions that are not allowed in a hard clause: SALU, export, branch,
62  // message, GDS, s_waitcnt and anything else not mentioned above.
63  HARDCLAUSE_ILLEGAL,
64 };
65 
66 class SIInsertHardClauses : public MachineFunctionPass {
67 public:
68  static char ID;
69  const GCNSubtarget *ST = nullptr;
70 
71  SIInsertHardClauses() : MachineFunctionPass(ID) {}
72 
73  void getAnalysisUsage(AnalysisUsage &AU) const override {
74  AU.setPreservesCFG();
76  }
77 
78  HardClauseType getHardClauseType(const MachineInstr &MI) {
79  // On current architectures we only get a benefit from clausing loads.
80  if (MI.mayLoad()) {
82  return HARDCLAUSE_VMEM;
84  return HARDCLAUSE_FLAT;
85  // TODO: LDS
87  return HARDCLAUSE_SMEM;
88  }
89 
90  // Don't form VALU clauses. It's not clear what benefit they give, if any.
91 
92  // In practice s_nop is the only internal instruction we're likely to see.
93  // It's safe to treat the rest as illegal.
94  if (MI.getOpcode() == AMDGPU::S_NOP)
95  return HARDCLAUSE_INTERNAL;
96  return HARDCLAUSE_ILLEGAL;
97  }
98 
99  // Track information about a clause as we discover it.
100  struct ClauseInfo {
101  // The type of all (non-internal) instructions in the clause.
102  HardClauseType Type = HARDCLAUSE_ILLEGAL;
103  // The first (necessarily non-internal) instruction in the clause.
104  MachineInstr *First = nullptr;
105  // The last non-internal instruction in the clause.
106  MachineInstr *Last = nullptr;
107  // The length of the clause including any internal instructions in the
108  // middle or after the end of the clause.
109  unsigned Length = 0;
110  // The base operands of *Last.
112  };
113 
114  bool emitClause(const ClauseInfo &CI, const SIInstrInfo *SII) {
115  // Get the size of the clause excluding any internal instructions at the
116  // end.
117  unsigned Size =
118  std::distance(CI.First->getIterator(), CI.Last->getIterator()) + 1;
119  if (Size < 2)
120  return false;
121  assert(Size <= 64 && "Hard clause is too long!");
122 
123  auto &MBB = *CI.First->getParent();
124  auto ClauseMI =
125  BuildMI(MBB, *CI.First, DebugLoc(), SII->get(AMDGPU::S_CLAUSE))
126  .addImm(Size - 1);
127  finalizeBundle(MBB, ClauseMI->getIterator(),
128  std::next(CI.Last->getIterator()));
129  return true;
130  }
131 
132  bool runOnMachineFunction(MachineFunction &MF) override {
133  if (skipFunction(MF.getFunction()))
134  return false;
135 
136  ST = &MF.getSubtarget<GCNSubtarget>();
137  if (!ST->hasHardClauses())
138  return false;
139 
140  const SIInstrInfo *SII = ST->getInstrInfo();
141  const TargetRegisterInfo *TRI = ST->getRegisterInfo();
142 
143  bool Changed = false;
144  for (auto &MBB : MF) {
145  ClauseInfo CI;
146  for (auto &MI : MBB) {
147  HardClauseType Type = getHardClauseType(MI);
148 
149  int64_t Dummy1;
150  bool Dummy2;
151  unsigned Dummy3;
153  if (Type <= LAST_REAL_HARDCLAUSE_TYPE) {
154  if (!SII->getMemOperandsWithOffsetWidth(MI, BaseOps, Dummy1, Dummy2,
155  Dummy3, TRI)) {
156  // We failed to get the base operands, so we'll never clause this
157  // instruction with any other, so pretend it's illegal.
158  Type = HARDCLAUSE_ILLEGAL;
159  }
160  }
161 
162  if (CI.Length == 64 ||
163  (CI.Length && Type != HARDCLAUSE_INTERNAL &&
164  (Type != CI.Type ||
165  // Note that we lie to shouldClusterMemOps about the size of the
166  // cluster. When shouldClusterMemOps is called from the machine
167  // scheduler it limits the size of the cluster to avoid increasing
168  // register pressure too much, but this pass runs after register
169  // allocation so there is no need for that kind of limit.
170  !SII->shouldClusterMemOps(CI.BaseOps, BaseOps, 2, 2)))) {
171  // Finish the current clause.
172  Changed |= emitClause(CI, SII);
173  CI = ClauseInfo();
174  }
175 
176  if (CI.Length) {
177  // Extend the current clause.
178  ++CI.Length;
179  if (Type != HARDCLAUSE_INTERNAL) {
180  CI.Last = &MI;
181  CI.BaseOps = std::move(BaseOps);
182  }
183  } else if (Type <= LAST_REAL_HARDCLAUSE_TYPE) {
184  // Start a new clause.
185  CI = ClauseInfo{Type, &MI, &MI, 1, std::move(BaseOps)};
186  }
187  }
188 
189  // Finish the last clause in the basic block if any.
190  if (CI.Length)
191  Changed |= emitClause(CI, SII);
192  }
193 
194  return Changed;
195  }
196 };
197 
198 } // namespace
199 
200 char SIInsertHardClauses::ID = 0;
201 
203 
204 INITIALIZE_PASS(SIInsertHardClauses, DEBUG_TYPE, "SI Insert Hard Clauses",
205  false, false)
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Definition: SIInsertHardClauses.cpp:202
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