1 //===---- CGLoopInfo.cpp - LLVM CodeGen for loop metadata -*- C++ -*-------===//
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 #include "CGLoopInfo.h"
11 #include "llvm/IR/BasicBlock.h"
12 #include "llvm/IR/Constants.h"
13 #include "llvm/IR/InstrTypes.h"
14 #include "llvm/IR/Instructions.h"
15 #include "llvm/IR/Metadata.h"
16 using namespace clang;
17 using namespace CodeGen;
18 using namespace llvm;
19 
20 static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs) {
21 
22   if (!Attrs.IsParallel && Attrs.VectorizerWidth == 0 &&
23       Attrs.VectorizerUnroll == 0 &&
24       Attrs.VectorizerEnable == LoopAttributes::VecUnspecified)
25     return nullptr;
26 
27   SmallVector<Metadata *, 4> Args;
28   // Reserve operand 0 for loop id self reference.
29   auto TempNode = MDNode::getTemporary(Ctx, None);
30   Args.push_back(TempNode.get());
31 
32   // Setting vectorizer.width
33   if (Attrs.VectorizerWidth > 0) {
34     Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.vectorize.width"),
35                         ConstantAsMetadata::get(ConstantInt::get(
36                             Type::getInt32Ty(Ctx), Attrs.VectorizerWidth))};
37     Args.push_back(MDNode::get(Ctx, Vals));
38   }
39 
40   // Setting vectorizer.unroll
41   if (Attrs.VectorizerUnroll > 0) {
42     Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.interleave.count"),
43                         ConstantAsMetadata::get(ConstantInt::get(
44                             Type::getInt32Ty(Ctx), Attrs.VectorizerUnroll))};
45     Args.push_back(MDNode::get(Ctx, Vals));
46   }
47 
48   // Setting vectorizer.enable
49   if (Attrs.VectorizerEnable != LoopAttributes::VecUnspecified) {
50     Metadata *Vals[] = {
51         MDString::get(Ctx, "llvm.loop.vectorize.enable"),
52         ConstantAsMetadata::get(ConstantInt::get(
53             Type::getInt1Ty(Ctx),
54             (Attrs.VectorizerEnable == LoopAttributes::VecEnable)))};
55     Args.push_back(MDNode::get(Ctx, Vals));
56   }
57 
58   // Set the first operand to itself.
59   MDNode *LoopID = MDNode::get(Ctx, Args);
60   LoopID->replaceOperandWith(0, LoopID);
61   return LoopID;
62 }
63 
64 LoopAttributes::LoopAttributes(bool IsParallel)
65     : IsParallel(IsParallel), VectorizerEnable(LoopAttributes::VecUnspecified),
66       VectorizerWidth(0), VectorizerUnroll(0) {}
67 
68 void LoopAttributes::clear() {
69   IsParallel = false;
70   VectorizerWidth = 0;
71   VectorizerUnroll = 0;
72   VectorizerEnable = LoopAttributes::VecUnspecified;
73 }
74 
75 LoopInfo::LoopInfo(BasicBlock *Header, const LoopAttributes &Attrs)
76     : LoopID(nullptr), Header(Header), Attrs(Attrs) {
77   LoopID = createMetadata(Header->getContext(), Attrs);
78 }
79 
80 void LoopInfoStack::push(BasicBlock *Header) {
81   Active.push_back(LoopInfo(Header, StagedAttrs));
82   // Clear the attributes so nested loops do not inherit them.
83   StagedAttrs.clear();
84 }
85 
86 void LoopInfoStack::pop() {
87   assert(!Active.empty() && "No active loops to pop");
88   Active.pop_back();
89 }
90 
91 void LoopInfoStack::InsertHelper(Instruction *I) const {
92   if (!hasInfo())
93     return;
94 
95   const LoopInfo &L = getInfo();
96   if (!L.getLoopID())
97     return;
98 
99   if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I)) {
100     for (unsigned i = 0, ie = TI->getNumSuccessors(); i < ie; ++i)
101       if (TI->getSuccessor(i) == L.getHeader()) {
102         TI->setMetadata("llvm.loop", L.getLoopID());
103         break;
104       }
105     return;
106   }
107 
108   if (L.getAttributes().IsParallel && I->mayReadOrWriteMemory())
109     I->setMetadata("llvm.mem.parallel_loop_access", L.getLoopID());
110 }
111