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
|
//===-- AMDGPUMemoryUtils.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
//
//===----------------------------------------------------------------------===//
#include "AMDGPUMemoryUtils.h"
#include "AMDGPU.h"
#include "AMDGPUBaseInfo.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/IntrinsicsAMDGPU.h"
#include "llvm/IR/ReplaceConstant.h"
#define DEBUG_TYPE "amdgpu-memory-utils"
using namespace llvm;
namespace llvm {
namespace AMDGPU {
Align getAlign(DataLayout const &DL, const GlobalVariable *GV) {
return DL.getValueOrABITypeAlignment(GV->getPointerAlignment(DL),
GV->getValueType());
}
static void collectFunctionUses(User *U, const Function *F,
SetVector<Instruction *> &InstUsers) {
SmallVector<User *> Stack{U};
while (!Stack.empty()) {
U = Stack.pop_back_val();
if (auto *I = dyn_cast<Instruction>(U)) {
if (I->getFunction() == F)
InstUsers.insert(I);
continue;
}
if (!isa<ConstantExpr>(U))
continue;
append_range(Stack, U->users());
}
}
void replaceConstantUsesInFunction(ConstantExpr *C, const Function *F) {
SetVector<Instruction *> InstUsers;
collectFunctionUses(C, F, InstUsers);
for (Instruction *I : InstUsers) {
convertConstantExprsToInstructions(I, C);
}
}
static bool shouldLowerLDSToStruct(const GlobalVariable &GV,
const Function *F) {
// We are not interested in kernel LDS lowering for module LDS itself.
if (F && GV.getName() == "llvm.amdgcn.module.lds")
return false;
bool Ret = false;
SmallPtrSet<const User *, 8> Visited;
SmallVector<const User *, 16> Stack(GV.users());
assert(!F || isKernelCC(F));
while (!Stack.empty()) {
const User *V = Stack.pop_back_val();
Visited.insert(V);
if (isa<GlobalValue>(V)) {
// This use of the LDS variable is the initializer of a global variable.
// This is ill formed. The address of an LDS variable is kernel dependent
// and unknown until runtime. It can't be written to a global variable.
continue;
}
if (auto *I = dyn_cast<Instruction>(V)) {
const Function *UF = I->getFunction();
if (UF == F) {
// Used from this kernel, we want to put it into the structure.
Ret = true;
} else if (!F) {
// For module LDS lowering, lowering is required if the user instruction
// is from non-kernel function.
Ret |= !isKernelCC(UF);
}
continue;
}
// User V should be a constant, recursively visit users of V.
assert(isa<Constant>(V) && "Expected a constant.");
append_range(Stack, V->users());
}
return Ret;
}
std::vector<GlobalVariable *> findVariablesToLower(Module &M,
const Function *F) {
std::vector<llvm::GlobalVariable *> LocalVars;
for (auto &GV : M.globals()) {
if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) {
continue;
}
if (!GV.hasInitializer()) {
// addrspace(3) without initializer implies cuda/hip extern __shared__
// the semantics for such a variable appears to be that all extern
// __shared__ variables alias one another, in which case this transform
// is not required
continue;
}
if (!isa<UndefValue>(GV.getInitializer())) {
// Initializers are unimplemented for LDS address space.
// Leave such variables in place for consistent error reporting.
continue;
}
if (GV.isConstant()) {
// A constant undef variable can't be written to, and any load is
// undef, so it should be eliminated by the optimizer. It could be
// dropped by the back end if not. This pass skips over it.
continue;
}
if (!shouldLowerLDSToStruct(GV, F)) {
continue;
}
LocalVars.push_back(&GV);
}
return LocalVars;
}
bool isReallyAClobber(const Value *Ptr, MemoryDef *Def, AAResults *AA) {
Instruction *DefInst = Def->getMemoryInst();
if (isa<FenceInst>(DefInst))
return false;
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) {
switch (II->getIntrinsicID()) {
case Intrinsic::amdgcn_s_barrier:
case Intrinsic::amdgcn_wave_barrier:
return false;
default:
break;
}
}
// Ignore atomics not aliasing with the original load, any atomic is a
// universal MemoryDef from MSSA's point of view too, just like a fence.
const auto checkNoAlias = [AA, Ptr](auto I) -> bool {
return I && AA->isNoAlias(I->getPointerOperand(), Ptr);
};
if (checkNoAlias(dyn_cast<AtomicCmpXchgInst>(DefInst)) ||
checkNoAlias(dyn_cast<AtomicRMWInst>(DefInst)))
return false;
return true;
}
bool isClobberedInFunction(const LoadInst *Load, MemorySSA *MSSA,
AAResults *AA) {
MemorySSAWalker *Walker = MSSA->getWalker();
SmallVector<MemoryAccess *> WorkList{Walker->getClobberingMemoryAccess(Load)};
SmallSet<MemoryAccess *, 8> Visited;
MemoryLocation Loc(MemoryLocation::get(Load));
LLVM_DEBUG(dbgs() << "Checking clobbering of: " << *Load << '\n');
// Start with a nearest dominating clobbering access, it will be either
// live on entry (nothing to do, load is not clobbered), MemoryDef, or
// MemoryPhi if several MemoryDefs can define this memory state. In that
// case add all Defs to WorkList and continue going up and checking all
// the definitions of this memory location until the root. When all the
// defs are exhausted and came to the entry state we have no clobber.
// Along the scan ignore barriers and fences which are considered clobbers
// by the MemorySSA, but not really writing anything into the memory.
while (!WorkList.empty()) {
MemoryAccess *MA = WorkList.pop_back_val();
if (!Visited.insert(MA).second)
continue;
if (MSSA->isLiveOnEntryDef(MA))
continue;
if (MemoryDef *Def = dyn_cast<MemoryDef>(MA)) {
LLVM_DEBUG(dbgs() << " Def: " << *Def->getMemoryInst() << '\n');
if (isReallyAClobber(Load->getPointerOperand(), Def, AA)) {
LLVM_DEBUG(dbgs() << " -> load is clobbered\n");
return true;
}
WorkList.push_back(
Walker->getClobberingMemoryAccess(Def->getDefiningAccess(), Loc));
continue;
}
const MemoryPhi *Phi = cast<MemoryPhi>(MA);
for (auto &Use : Phi->incoming_values())
WorkList.push_back(cast<MemoryAccess>(&Use));
}
LLVM_DEBUG(dbgs() << " -> no clobber\n");
return false;
}
} // end namespace AMDGPU
} // end namespace llvm
|
