1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
| //===-- SIOptimizeExecMaskingPreRA.cpp ------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This pass removes redundant S_OR_B64 instructions enabling lanes in
/// the exec. If two SI_END_CF (lowered as S_OR_B64) come together without any
/// vector instructions between them we can only keep outer SI_END_CF, given
/// that CFG is structured and exec bits of the outer end statement are always
/// not less than exec bit of the inner one.
///
/// This needs to be done before the RA to eliminate saved exec bits registers
/// but after register coalescer to have no vector registers copies in between
/// of different end cf statements.
///
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "AMDGPUSubtarget.h"
#include "SIInstrInfo.h"
#include "MCTargetDesc/AMDGPUMCTargetDesc.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
using namespace llvm;
#define DEBUG_TYPE "si-optimize-exec-masking-pre-ra"
namespace {
class SIOptimizeExecMaskingPreRA : public MachineFunctionPass {
private:
const SIRegisterInfo *TRI;
const SIInstrInfo *TII;
MachineRegisterInfo *MRI;
public:
MachineBasicBlock::iterator skipIgnoreExecInsts(
MachineBasicBlock::iterator I, MachineBasicBlock::iterator E) const;
MachineBasicBlock::iterator skipIgnoreExecInstsTrivialSucc(
MachineBasicBlock *&MBB,
MachineBasicBlock::iterator It) const;
public:
static char ID;
SIOptimizeExecMaskingPreRA() : MachineFunctionPass(ID) {
initializeSIOptimizeExecMaskingPreRAPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
StringRef getPassName() const override {
return "SI optimize exec mask operations pre-RA";
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LiveIntervals>();
AU.setPreservesAll();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
} // End anonymous namespace.
INITIALIZE_PASS_BEGIN(SIOptimizeExecMaskingPreRA, DEBUG_TYPE,
"SI optimize exec mask operations pre-RA", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(SIOptimizeExecMaskingPreRA, DEBUG_TYPE,
"SI optimize exec mask operations pre-RA", false, false)
char SIOptimizeExecMaskingPreRA::ID = 0;
char &llvm::SIOptimizeExecMaskingPreRAID = SIOptimizeExecMaskingPreRA::ID;
FunctionPass *llvm::createSIOptimizeExecMaskingPreRAPass() {
return new SIOptimizeExecMaskingPreRA();
}
static bool isEndCF(const MachineInstr &MI, const SIRegisterInfo *TRI,
const GCNSubtarget &ST) {
if (ST.isWave32()) {
return MI.getOpcode() == AMDGPU::S_OR_B32 &&
MI.modifiesRegister(AMDGPU::EXEC_LO, TRI);
}
return MI.getOpcode() == AMDGPU::S_OR_B64 &&
MI.modifiesRegister(AMDGPU::EXEC, TRI);
}
static bool isFullExecCopy(const MachineInstr& MI, const GCNSubtarget& ST) {
unsigned Exec = ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC;
if (MI.isCopy() && MI.getOperand(1).getReg() == Exec) {
assert(MI.isFullCopy());
return true;
}
return false;
}
static unsigned getOrNonExecReg(const MachineInstr &MI,
const SIInstrInfo &TII,
const GCNSubtarget& ST) {
unsigned Exec = ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC;
auto Op = TII.getNamedOperand(MI, AMDGPU::OpName::src1);
if (Op->isReg() && Op->getReg() != Exec)
return Op->getReg();
Op = TII.getNamedOperand(MI, AMDGPU::OpName::src0);
if (Op->isReg() && Op->getReg() != Exec)
return Op->getReg();
return AMDGPU::NoRegister;
}
static MachineInstr* getOrExecSource(const MachineInstr &MI,
const SIInstrInfo &TII,
const MachineRegisterInfo &MRI,
const GCNSubtarget& ST) {
auto SavedExec = getOrNonExecReg(MI, TII, ST);
if (SavedExec == AMDGPU::NoRegister)
return nullptr;
auto SaveExecInst = MRI.getUniqueVRegDef(SavedExec);
if (!SaveExecInst || !isFullExecCopy(*SaveExecInst, ST))
return nullptr;
return SaveExecInst;
}
/// Skip over instructions that don't care about the exec mask.
MachineBasicBlock::iterator SIOptimizeExecMaskingPreRA::skipIgnoreExecInsts(
MachineBasicBlock::iterator I, MachineBasicBlock::iterator E) const {
for ( ; I != E; ++I) {
if (TII->mayReadEXEC(*MRI, *I))
break;
}
return I;
}
// Skip to the next instruction, ignoring debug instructions, and trivial block
// boundaries (blocks that have one (typically fallthrough) successor, and the
// successor has one predecessor.
MachineBasicBlock::iterator
SIOptimizeExecMaskingPreRA::skipIgnoreExecInstsTrivialSucc(
MachineBasicBlock *&MBB,
MachineBasicBlock::iterator It) const {
do {
It = skipIgnoreExecInsts(It, MBB->end());
if (It != MBB->end() || MBB->succ_size() != 1)
break;
// If there is one trivial successor, advance to the next block.
MachineBasicBlock *Succ = *MBB->succ_begin();
// TODO: Is this really necessary?
if (!MBB->isLayoutSuccessor(Succ))
break;
It = Succ->begin();
MBB = Succ;
} while (true);
return It;
}
// Optimize sequence
// %sel = V_CNDMASK_B32_e64 0, 1, %cc
// %cmp = V_CMP_NE_U32 1, %1
// $vcc = S_AND_B64 $exec, %cmp
// S_CBRANCH_VCC[N]Z
// =>
// $vcc = S_ANDN2_B64 $exec, %cc
// S_CBRANCH_VCC[N]Z
//
// It is the negation pattern inserted by DAGCombiner::visitBRCOND() in the
// rebuildSetCC(). We start with S_CBRANCH to avoid exhaustive search, but
// only 3 first instructions are really needed. S_AND_B64 with exec is a
// required part of the pattern since V_CNDMASK_B32 writes zeroes for inactive
// lanes.
//
// Returns %cc register on success.
static unsigned optimizeVcndVcmpPair(MachineBasicBlock &MBB,
const GCNSubtarget &ST,
MachineRegisterInfo &MRI,
LiveIntervals *LIS) {
const SIRegisterInfo *TRI = ST.getRegisterInfo();
const SIInstrInfo *TII = ST.getInstrInfo();
bool Wave32 = ST.isWave32();
const unsigned AndOpc = Wave32 ? AMDGPU::S_AND_B32 : AMDGPU::S_AND_B64;
const unsigned Andn2Opc = Wave32 ? AMDGPU::S_ANDN2_B32 : AMDGPU::S_ANDN2_B64;
const unsigned CondReg = Wave32 ? AMDGPU::VCC_LO : AMDGPU::VCC;
const unsigned ExecReg = Wave32 ? AMDGPU::EXEC_LO : AMDGPU::EXEC;
auto I = llvm::find_if(MBB.terminators(), [](const MachineInstr &MI) {
unsigned Opc = MI.getOpcode();
return Opc == AMDGPU::S_CBRANCH_VCCZ ||
Opc == AMDGPU::S_CBRANCH_VCCNZ; });
if (I == MBB.terminators().end())
return AMDGPU::NoRegister;
auto *And = TRI->findReachingDef(CondReg, AMDGPU::NoSubRegister,
*I, MRI, LIS);
if (!And || And->getOpcode() != AndOpc ||
!And->getOperand(1).isReg() || !And->getOperand(2).isReg())
return AMDGPU::NoRegister;
MachineOperand *AndCC = &And->getOperand(1);
Register CmpReg = AndCC->getReg();
unsigned CmpSubReg = AndCC->getSubReg();
if (CmpReg == ExecReg) {
AndCC = &And->getOperand(2);
CmpReg = AndCC->getReg();
CmpSubReg = AndCC->getSubReg();
} else if (And->getOperand(2).getReg() != ExecReg) {
return AMDGPU::NoRegister;
}
auto *Cmp = TRI->findReachingDef(CmpReg, CmpSubReg, *And, MRI, LIS);
if (!Cmp || !(Cmp->getOpcode() == AMDGPU::V_CMP_NE_U32_e32 ||
Cmp->getOpcode() == AMDGPU::V_CMP_NE_U32_e64) ||
Cmp->getParent() != And->getParent())
return AMDGPU::NoRegister;
MachineOperand *Op1 = TII->getNamedOperand(*Cmp, AMDGPU::OpName::src0);
MachineOperand *Op2 = TII->getNamedOperand(*Cmp, AMDGPU::OpName::src1);
if (Op1->isImm() && Op2->isReg())
std::swap(Op1, Op2);
if (!Op1->isReg() || !Op2->isImm() || Op2->getImm() != 1)
return AMDGPU::NoRegister;
Register SelReg = Op1->getReg();
auto *Sel = TRI->findReachingDef(SelReg, Op1->getSubReg(), *Cmp, MRI, LIS);
if (!Sel || Sel->getOpcode() != AMDGPU::V_CNDMASK_B32_e64)
return AMDGPU::NoRegister;
if (TII->hasModifiersSet(*Sel, AMDGPU::OpName::src0_modifiers) ||
TII->hasModifiersSet(*Sel, AMDGPU::OpName::src1_modifiers))
return AMDGPU::NoRegister;
Op1 = TII->getNamedOperand(*Sel, AMDGPU::OpName::src0);
Op2 = TII->getNamedOperand(*Sel, AMDGPU::OpName::src1);
MachineOperand *CC = TII->getNamedOperand(*Sel, AMDGPU::OpName::src2);
if (!Op1->isImm() || !Op2->isImm() || !CC->isReg() ||
Op1->getImm() != 0 || Op2->getImm() != 1)
return AMDGPU::NoRegister;
LLVM_DEBUG(dbgs() << "Folding sequence:\n\t" << *Sel << '\t' << *Cmp << '\t'
<< *And);
Register CCReg = CC->getReg();
LIS->RemoveMachineInstrFromMaps(*And);
MachineInstr *Andn2 =
BuildMI(MBB, *And, And->getDebugLoc(), TII->get(Andn2Opc),
And->getOperand(0).getReg())
.addReg(ExecReg)
.addReg(CCReg, getUndefRegState(CC->isUndef()), CC->getSubReg());
And->eraseFromParent();
LIS->InsertMachineInstrInMaps(*Andn2);
LLVM_DEBUG(dbgs() << "=>\n\t" << *Andn2 << '\n');
// Try to remove compare. Cmp value should not used in between of cmp
// and s_and_b64 if VCC or just unused if any other register.
if ((Register::isVirtualRegister(CmpReg) && MRI.use_nodbg_empty(CmpReg)) ||
(CmpReg == CondReg &&
std::none_of(std::next(Cmp->getIterator()), Andn2->getIterator(),
[&](const MachineInstr &MI) {
return MI.readsRegister(CondReg, TRI);
}))) {
LLVM_DEBUG(dbgs() << "Erasing: " << *Cmp << '\n');
LIS->RemoveMachineInstrFromMaps(*Cmp);
Cmp->eraseFromParent();
// Try to remove v_cndmask_b32.
if (Register::isVirtualRegister(SelReg) && MRI.use_nodbg_empty(SelReg)) {
LLVM_DEBUG(dbgs() << "Erasing: " << *Sel << '\n');
LIS->RemoveMachineInstrFromMaps(*Sel);
Sel->eraseFromParent();
}
}
return CCReg;
}
bool SIOptimizeExecMaskingPreRA::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
TRI = ST.getRegisterInfo();
TII = ST.getInstrInfo();
MRI = &MF.getRegInfo();
MachineRegisterInfo &MRI = MF.getRegInfo();
LiveIntervals *LIS = &getAnalysis<LiveIntervals>();
DenseSet<unsigned> RecalcRegs({AMDGPU::EXEC_LO, AMDGPU::EXEC_HI});
unsigned Exec = ST.isWave32() ? AMDGPU::EXEC_LO : AMDGPU::EXEC;
bool Changed = false;
for (MachineBasicBlock &MBB : MF) {
if (unsigned Reg = optimizeVcndVcmpPair(MBB, ST, MRI, LIS)) {
RecalcRegs.insert(Reg);
RecalcRegs.insert(AMDGPU::VCC_LO);
RecalcRegs.insert(AMDGPU::VCC_HI);
RecalcRegs.insert(AMDGPU::SCC);
Changed = true;
}
// Try to remove unneeded instructions before s_endpgm.
if (MBB.succ_empty()) {
if (MBB.empty())
continue;
// Skip this if the endpgm has any implicit uses, otherwise we would need
// to be careful to update / remove them.
// S_ENDPGM always has a single imm operand that is not used other than to
// end up in the encoding
MachineInstr &Term = MBB.back();
if (Term.getOpcode() != AMDGPU::S_ENDPGM || Term.getNumOperands() != 1)
continue;
SmallVector<MachineBasicBlock*, 4> Blocks({&MBB});
while (!Blocks.empty()) {
auto CurBB = Blocks.pop_back_val();
auto I = CurBB->rbegin(), E = CurBB->rend();
if (I != E) {
if (I->isUnconditionalBranch() || I->getOpcode() == AMDGPU::S_ENDPGM)
++I;
else if (I->isBranch())
continue;
}
while (I != E) {
if (I->isDebugInstr()) {
I = std::next(I);
continue;
}
if (I->mayStore() || I->isBarrier() || I->isCall() ||
I->hasUnmodeledSideEffects() || I->hasOrderedMemoryRef())
break;
LLVM_DEBUG(dbgs()
<< "Removing no effect instruction: " << *I << '\n');
for (auto &Op : I->operands()) {
if (Op.isReg())
RecalcRegs.insert(Op.getReg());
}
auto Next = std::next(I);
LIS->RemoveMachineInstrFromMaps(*I);
I->eraseFromParent();
I = Next;
Changed = true;
}
if (I != E)
continue;
// Try to ascend predecessors.
for (auto *Pred : CurBB->predecessors()) {
if (Pred->succ_size() == 1)
Blocks.push_back(Pred);
}
}
continue;
}
// Try to collapse adjacent endifs.
auto E = MBB.end();
auto Lead = skipDebugInstructionsForward(MBB.begin(), E);
if (MBB.succ_size() != 1 || Lead == E || !isEndCF(*Lead, TRI, ST))
continue;
MachineBasicBlock *TmpMBB = &MBB;
auto NextLead = skipIgnoreExecInstsTrivialSucc(TmpMBB, std::next(Lead));
if (NextLead == TmpMBB->end() || !isEndCF(*NextLead, TRI, ST) ||
!getOrExecSource(*NextLead, *TII, MRI, ST))
continue;
LLVM_DEBUG(dbgs() << "Redundant EXEC = S_OR_B64 found: " << *Lead << '\n');
auto SaveExec = getOrExecSource(*Lead, *TII, MRI, ST);
unsigned SaveExecReg = getOrNonExecReg(*Lead, *TII, ST);
for (auto &Op : Lead->operands()) {
if (Op.isReg())
RecalcRegs.insert(Op.getReg());
}
LIS->RemoveMachineInstrFromMaps(*Lead);
Lead->eraseFromParent();
if (SaveExecReg) {
LIS->removeInterval(SaveExecReg);
LIS->createAndComputeVirtRegInterval(SaveExecReg);
}
Changed = true;
// If the only use of saved exec in the removed instruction is S_AND_B64
// fold the copy now.
if (!SaveExec || !SaveExec->isFullCopy())
continue;
Register SavedExec = SaveExec->getOperand(0).getReg();
bool SafeToReplace = true;
for (auto& U : MRI.use_nodbg_instructions(SavedExec)) {
if (U.getParent() != SaveExec->getParent()) {
SafeToReplace = false;
break;
}
LLVM_DEBUG(dbgs() << "Redundant EXEC COPY: " << *SaveExec << '\n');
}
if (SafeToReplace) {
LIS->RemoveMachineInstrFromMaps(*SaveExec);
SaveExec->eraseFromParent();
MRI.replaceRegWith(SavedExec, Exec);
LIS->removeInterval(SavedExec);
}
}
if (Changed) {
for (auto Reg : RecalcRegs) {
if (Register::isVirtualRegister(Reg)) {
LIS->removeInterval(Reg);
if (!MRI.reg_empty(Reg))
LIS->createAndComputeVirtRegInterval(Reg);
} else {
LIS->removeAllRegUnitsForPhysReg(Reg);
}
}
}
return Changed;
}
|