xref: /netbsd-src/external/apache2/llvm/dist/llvm/lib/Target/AMDGPU/Utils/AMDGPULDSUtils.cpp (revision 82d56013d7b633d116a93943de88e08335357a7c)
1 //===- AMDGPULDSUtils.cpp -------------------------------------------------===//
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 // AMDGPU LDS related helper utility functions.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "AMDGPULDSUtils.h"
14 #include "Utils/AMDGPUBaseInfo.h"
15 #include "llvm/IR/Constants.h"
16 
17 using namespace llvm;
18 
19 namespace llvm {
20 
21 namespace AMDGPU {
22 
isKernelCC(Function * Func)23 bool isKernelCC(Function *Func) {
24   return AMDGPU::isModuleEntryFunctionCC(Func->getCallingConv());
25 }
26 
getAlign(DataLayout const & DL,const GlobalVariable * GV)27 Align getAlign(DataLayout const &DL, const GlobalVariable *GV) {
28   return DL.getValueOrABITypeAlignment(GV->getPointerAlignment(DL),
29                                        GV->getValueType());
30 }
31 
userRequiresLowering(const SmallPtrSetImpl<GlobalValue * > & UsedList,User * InitialUser)32 bool userRequiresLowering(const SmallPtrSetImpl<GlobalValue *> &UsedList,
33                           User *InitialUser) {
34   // Any LDS variable can be lowered by moving into the created struct
35   // Each variable so lowered is allocated in every kernel, so variables
36   // whose users are all known to be safe to lower without the transform
37   // are left unchanged.
38   SmallPtrSet<User *, 8> Visited;
39   SmallVector<User *, 16> Stack;
40   Stack.push_back(InitialUser);
41 
42   while (!Stack.empty()) {
43     User *V = Stack.pop_back_val();
44     Visited.insert(V);
45 
46     if (auto *G = dyn_cast<GlobalValue>(V->stripPointerCasts())) {
47       if (UsedList.contains(G)) {
48         continue;
49       }
50     }
51 
52     if (auto *I = dyn_cast<Instruction>(V)) {
53       if (isKernelCC(I->getFunction())) {
54         continue;
55       }
56     }
57 
58     if (auto *E = dyn_cast<ConstantExpr>(V)) {
59       for (Value::user_iterator EU = E->user_begin(); EU != E->user_end();
60            ++EU) {
61         if (Visited.insert(*EU).second) {
62           Stack.push_back(*EU);
63         }
64       }
65       continue;
66     }
67 
68     // Unknown user, conservatively lower the variable
69     return true;
70   }
71 
72   return false;
73 }
74 
75 std::vector<GlobalVariable *>
findVariablesToLower(Module & M,const SmallPtrSetImpl<GlobalValue * > & UsedList)76 findVariablesToLower(Module &M,
77                      const SmallPtrSetImpl<GlobalValue *> &UsedList) {
78   std::vector<llvm::GlobalVariable *> LocalVars;
79   for (auto &GV : M.globals()) {
80     if (GV.getType()->getPointerAddressSpace() != AMDGPUAS::LOCAL_ADDRESS) {
81       continue;
82     }
83     if (!GV.hasInitializer()) {
84       // addrspace(3) without initializer implies cuda/hip extern __shared__
85       // the semantics for such a variable appears to be that all extern
86       // __shared__ variables alias one another, in which case this transform
87       // is not required
88       continue;
89     }
90     if (!isa<UndefValue>(GV.getInitializer())) {
91       // Initializers are unimplemented for local address space.
92       // Leave such variables in place for consistent error reporting.
93       continue;
94     }
95     if (GV.isConstant()) {
96       // A constant undef variable can't be written to, and any load is
97       // undef, so it should be eliminated by the optimizer. It could be
98       // dropped by the back end if not. This pass skips over it.
99       continue;
100     }
101     if (std::none_of(GV.user_begin(), GV.user_end(), [&](User *U) {
102           return userRequiresLowering(UsedList, U);
103         })) {
104       continue;
105     }
106     LocalVars.push_back(&GV);
107   }
108   return LocalVars;
109 }
110 
getUsedList(Module & M)111 SmallPtrSet<GlobalValue *, 32> getUsedList(Module &M) {
112   SmallPtrSet<GlobalValue *, 32> UsedList;
113 
114   SmallVector<GlobalValue *, 32> TmpVec;
115   collectUsedGlobalVariables(M, TmpVec, true);
116   UsedList.insert(TmpVec.begin(), TmpVec.end());
117 
118   TmpVec.clear();
119   collectUsedGlobalVariables(M, TmpVec, false);
120   UsedList.insert(TmpVec.begin(), TmpVec.end());
121 
122   return UsedList;
123 }
124 
125 } // end namespace AMDGPU
126 
127 } // end namespace llvm
128