LLVM学习笔记（16）补

2.4.2.4.2. PatFrag的展开

在第一步完成后，我们为所有的PatFrag生成了TreePattern实例。接着，2490行的for循环对其中的片段进行展开。在第一次调用ParsePatternFragments()时（CodeGenDAGPatterns构造函数的2355行），展开输入模式。在第二次调用时（CodeGenDAGPatterns构造函数的2358行），展开输出模式（OutPatFrag定义）。展开由TreePattern的InlinePatternFragments()方法执行：

601       void InlinePatternFragments() {

602         for (unsigned i = 0, e = Trees.size(); i != e; ++i)

603           Trees[i] = Trees[i]->InlinePatternFragments(*this);

604       }

实际上PatFrag都只包含一棵TreePatternNode树。不过其他结构，比如Pattern，Instruction都会调用这个函数，它们可能有多棵树。每棵树的展开由TreePatternNode::InlinePatternFragments()方法来完成。

1358  TreePatternNode *TreePatternNode::InlinePatternFragments(TreePattern &TP) {

1359    if (TP.hasError())

1360      return nullptr;

1361 

1362    if (isLeaf())

1363       return this;  // nothing to do.

1364    Record *Op = getOperator();

1365 

1366    if (!Op->isSubClassOf("PatFrag")) {

1367      // Just recursively inline children nodes.

1368      for (unsigned i = 0, e = getNumChildren(); i != e; ++i) {

1369        TreePatternNode *Child = getChild(i);

1370        TreePatternNode *NewChild = Child->InlinePatternFragments(TP);

1371 

1372        assert((Child->getPredicateFns().empty() ||

1373                NewChild->getPredicateFns() == Child->getPredicateFns()) &&

1374               "Non-empty child predicate clobbered!");

1375 

1376        setChild(i, NewChild);

1377      }

1378      return this;

1379    }

1380 

1381    // Otherwise, we found a reference to a fragment.  First, look up its

1382    // TreePattern record.

1383    TreePattern *Frag = TP.getDAGPatterns().getPatternFragment(Op);

1384 

1385    // Verify that we are passing the right number of operands.

1386    if (Frag->getNumArgs() != Children.size()) {

1387      TP.error("'" + Op->getName() + "' fragment requires " +

1388               utostr(Frag->getNumArgs()) + " operands!");

1389      return nullptr;

1390    }

1391 

1392   TreePatternNode *FragTree = Frag->getOnlyTree()->clone();

1393 

1394    TreePredicateFn PredFn(Frag);

1395    if (!PredFn.isAlwaysTrue())

1396      FragTree->addPredicateFn(PredFn);

1397 

1398    // Resolve formal arguments to their actual value.

1399    if (Frag->getNumArgs()) {

1400      // Compute the map of formal to actual arguments.

1401      std::map<std::string, TreePatternNode*> ArgMap;

1402      for (unsigned i = 0, e = Frag->getNumArgs(); i != e; ++i)

1403        ArgMap[Frag->getArgName(i)] = getChild(i)->InlinePatternFragments(TP);

1404 

1405      FragTree->SubstituteFormalArguments(ArgMap);

1406    }

1407 

1408    FragTree->setName(getName());

1409    for (unsigned i = 0, e = Types.size(); i != e; ++i)

1410      FragTree->