TableGen: convert InstAlias's Emit bit to an int.

When multiple aliases overlap, the correct string to print can often be
determined purely by considering the InstAlias declarations in some particular
order. This allows the user to specify that order manually when desired,
without resorting to hacking around with the default lexicographical order on
Record instantiation, which is error-prone and ugly.

I was also mistaken about "add w2, w3, w4" being the same as "add w2, w3, w4,
uxtw". That's only true if Rn is the stack pointer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209199 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/AsmWriterEmitter.cpp

@@ -750,6 +750,23 @@ static unsigned CountNumOperands(StringRef AsmString, unsigned Variant) {
   return AsmString.count(' ') + AsmString.count('\t');
 }
 
+namespace {
+struct AliasPriorityComparator {
+  typedef std::pair<CodeGenInstAlias *, int> ValueType;
+  bool operator()(const ValueType &LHS, const ValueType &RHS) {
+    if (LHS.second ==  RHS.second) {
+      // We don't actually care about the order, but for consistency it
+      // shouldn't depend on pointer comparisons.
+      return LHS.first->TheDef->getName() < RHS.first->TheDef->getName();
+    }
+
+    // Aliases with larger priorities should be considered first.
+    return LHS.second > RHS.second;
+  }
+};
+}
+
+
 void AsmWriterEmitter::EmitPrintAliasInstruction(raw_ostream &O) {
   Record *AsmWriter = Target.getAsmWriter();
 
@@ -762,35 +779,36 @@ void AsmWriterEmitter::EmitPrintAliasInstruction(raw_ostream &O) {
 
   // Emit the method that prints the alias instruction.
   std::string ClassName = AsmWriter->getValueAsString("AsmWriterClassName");
+  unsigned Variant = AsmWriter->getValueAsInt("Variant");
 
   std::vector<Record*> AllInstAliases =
     Records.getAllDerivedDefinitions("InstAlias");
 
   // Create a map from the qualified name to a list of potential matches.
-  std::map<std::string, std::vector<CodeGenInstAlias*> > AliasMap;
-  unsigned Variant = AsmWriter->getValueAsInt("Variant");
+  typedef std::set<std::pair<CodeGenInstAlias*, int>, AliasPriorityComparator>
+      AliasWithPriority;
+  std::map<std::string, AliasWithPriority> AliasMap;
   for (std::vector<Record*>::iterator
          I = AllInstAliases.begin(), E = AllInstAliases.end(); I != E; ++I) {
     CodeGenInstAlias *Alias = new CodeGenInstAlias(*I, Variant, Target);
     const Record *R = *I;
-    if (!R->getValueAsBit("EmitAlias"))
-      continue; // We were told not to emit the alias, but to emit the aliasee.
+    int Priority = R->getValueAsInt("EmitPriority");
+    if (Priority < 1)
+      continue; // Aliases with priority 0 are never emitted.
+
     const DagInit *DI = R->getValueAsDag("ResultInst");
     const DefInit *Op = cast<DefInit>(DI->getOperator());
-    AliasMap[getQualifiedName(Op->getDef())].push_back(Alias);
+    AliasMap[getQualifiedName(Op->getDef())].insert(std::make_pair(Alias,
+                                                                   Priority));
   }
 
   // A map of which conditions need to be met for each instruction operand
   // before it can be matched to the mnemonic.
   std::map<std::string, std::vector<IAPrinter*> > IAPrinterMap;
 
-  for (std::map<std::string, std::vector<CodeGenInstAlias*> >::iterator
-         I = AliasMap.begin(), E = AliasMap.end(); I != E; ++I) {
-    std::vector<CodeGenInstAlias*> &Aliases = I->second;
-
-    for (std::vector<CodeGenInstAlias*>::iterator
-           II = Aliases.begin(), IE = Aliases.end(); II != IE; ++II) {
-      const CodeGenInstAlias *CGA = *II;
+  for (auto &Aliases : AliasMap) {
+    for (auto &Alias : Aliases.second) {
+      const CodeGenInstAlias *CGA = Alias.first;
       unsigned LastOpNo = CGA->ResultInstOperandIndex.size();
       unsigned NumResultOps =
         CountNumOperands(CGA->ResultInst->AsmString, Variant);
@@ -900,7 +918,7 @@ void AsmWriterEmitter::EmitPrintAliasInstruction(raw_ostream &O) {
       }
 
       if (CantHandle) continue;
-      IAPrinterMap[I->first].push_back(IAP);
+      IAPrinterMap[Aliases.first].push_back(IAP);
     }
   }