1 //===------ PollyIRBuilder.cpp --------------------------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // The Polly IRBuilder file contains Polly specific extensions for the IRBuilder
11 // that are used e.g. to emit the llvm.loop.parallel metadata.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "polly/CodeGen/IRBuilder.h"
16 
17 #include "polly/ScopInfo.h"
18 #include "polly/Support/ScopHelper.h"
19 
20 #include "llvm/IR/Metadata.h"
21 #include "llvm/Support/Debug.h"
22 
23 using namespace llvm;
24 using namespace polly;
25 
26 /// @brief Get a self referencing id metadata node.
27 ///
28 /// The MDNode looks like this (if arg0/arg1 are not null):
29 ///
30 ///    '!n = metadata !{metadata !n, arg0, arg1}'
31 ///
32 /// @return The self referencing id metadata node.
33 static MDNode *getID(LLVMContext &Ctx, Metadata *arg0 = nullptr,
34                      Metadata *arg1 = nullptr) {
35   MDNode *ID;
36   SmallVector<Metadata *, 3> Args;
37   // Use a temporary node to safely create a unique pointer for the first arg.
38   auto TempNode = MDNode::getTemporary(Ctx, None);
39   // Reserve operand 0 for loop id self reference.
40   Args.push_back(TempNode.get());
41 
42   if (arg0)
43     Args.push_back(arg0);
44   if (arg1)
45     Args.push_back(arg1);
46 
47   ID = MDNode::get(Ctx, Args);
48   ID->replaceOperandWith(0, ID);
49   return ID;
50 }
51 
52 ScopAnnotator::ScopAnnotator() : SE(nullptr), AliasScopeDomain(nullptr) {}
53 
54 void ScopAnnotator::buildAliasScopes(Scop &S) {
55   SE = S.getSE();
56 
57   LLVMContext &Ctx = SE->getContext();
58   AliasScopeDomain = getID(Ctx, MDString::get(Ctx, "polly.alias.scope.domain"));
59 
60   AliasScopeMap.clear();
61   OtherAliasScopeListMap.clear();
62 
63   SetVector<Value *> BasePtrs;
64   for (ScopStmt *Stmt : S)
65     for (MemoryAccess *MA : *Stmt)
66       BasePtrs.insert(MA->getBaseAddr());
67 
68   std::string AliasScopeStr = "polly.alias.scope.";
69   for (Value *BasePtr : BasePtrs)
70     AliasScopeMap[BasePtr] = getID(
71         Ctx, AliasScopeDomain,
72         MDString::get(Ctx, (AliasScopeStr + BasePtr->getName()).str().c_str()));
73 
74   for (Value *BasePtr : BasePtrs) {
75     MDNode *AliasScopeList = MDNode::get(Ctx, {});
76     for (const auto &AliasScopePair : AliasScopeMap) {
77       if (BasePtr == AliasScopePair.first)
78         continue;
79 
80       Metadata *Args = {AliasScopePair.second};
81       AliasScopeList =
82           MDNode::concatenate(AliasScopeList, MDNode::get(Ctx, Args));
83     }
84 
85     OtherAliasScopeListMap[BasePtr] = AliasScopeList;
86   }
87 }
88 
89 void ScopAnnotator::pushLoop(Loop *L, bool IsParallel) {
90 
91   ActiveLoops.push_back(L);
92   if (!IsParallel)
93     return;
94 
95   BasicBlock *Header = L->getHeader();
96   MDNode *Id = getID(Header->getContext());
97   assert(Id->getOperand(0) == Id && "Expected Id to be a self-reference");
98   assert(Id->getNumOperands() == 1 && "Unexpected extra operands in Id");
99   MDNode *Ids = ParallelLoops.empty()
100                     ? Id
101                     : MDNode::concatenate(ParallelLoops.back(), Id);
102   ParallelLoops.push_back(Ids);
103 }
104 
105 void ScopAnnotator::popLoop(bool IsParallel) {
106   ActiveLoops.pop_back();
107   if (!IsParallel)
108     return;
109 
110   assert(!ParallelLoops.empty() && "Expected a parallel loop to pop");
111   ParallelLoops.pop_back();
112 }
113 
114 void ScopAnnotator::annotateLoopLatch(BranchInst *B, Loop *L,
115                                       bool IsParallel) const {
116   if (!IsParallel)
117     return;
118 
119   assert(!ParallelLoops.empty() && "Expected a parallel loop to annotate");
120   MDNode *Ids = ParallelLoops.back();
121   MDNode *Id = cast<MDNode>(Ids->getOperand(Ids->getNumOperands() - 1));
122   B->setMetadata("llvm.loop", Id);
123 }
124 
125 void ScopAnnotator::annotate(Instruction *Inst) {
126   if (!Inst->mayReadOrWriteMemory())
127     return;
128 
129   // TODO: Use the ScopArrayInfo once available here.
130   if (AliasScopeDomain) {
131     Value *BasePtr = nullptr;
132     if (isa<StoreInst>(Inst) || isa<LoadInst>(Inst)) {
133       const SCEV *PtrSCEV = SE->getSCEV(getPointerOperand(*Inst));
134       const SCEV *BaseSCEV = SE->getPointerBase(PtrSCEV);
135       if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(BaseSCEV))
136         BasePtr = SU->getValue();
137     }
138 
139     if (BasePtr) {
140       Inst->setMetadata("alias.scope", AliasScopeMap[BasePtr]);
141       Inst->setMetadata("noalias", OtherAliasScopeListMap[BasePtr]);
142     }
143   }
144 
145   if (ParallelLoops.empty())
146     return;
147 
148   Inst->setMetadata("llvm.mem.parallel_loop_access", ParallelLoops.back());
149 }
150