[demangler][NFC] Tweak legacy uuidof handling

[urnathan]

Summary

We have to special-case 'u 8__uuidof [tz]' demangling for legacy support. That handling is a little duplicative.

• It seems better to just push the single expected node.

• We can also use 'consumeIf' rather than open-coding the peeking and increment.

• We don't need the numLeft < 2 check, as if there are few than that other paths will end up with detecting the error.

FWIW This simplifies a future change adding operator precedence.

ETA: Removes about 150 bytes of code (x86_64)

[ChuanqiXu]

llvm/include/llvm/Demangle/ItaniumDemangle.h

5046–5047

We could move this one before the place it get used.

[urnathan]

llvm/include/llvm/Demangle/ItaniumDemangle.h

5046–5047

No, we need to record the current High Water Mark of the Names array.

libcxxabi/src/demangle/ItaniumDemangle.h

case 'u': {
     Node *Name = getDerived().parseSourceName(/*NameState=*/nullptr);
     if (!Name)
       return nullptr;
     // Special case legacy __uuidof mangling. The 't' and 'z' appear where the
     // standard encoding expects a <template-arg>, and would be otherwise be
     // interpreted as <type> node 'short' or 'ellipsis'. However, neither
     // __uuidof(short) nor __uuidof(...) can actually appear, so there is no
     // actual conflict here.
+    bool IsUUID = false;
+    Node *UUID = nullptr;
     if (Name->getBaseName() == "__uuidof") {
-      if (numLeft() < 2)
-        return nullptr;
-      if (*First == 't') {
-        ++First;
-        Node *Ty = getDerived().parseType();
-        if (!Ty)
-          return nullptr;
-        return make<CallExpr>(Name, makeNodeArray(&Ty, &Ty + 1));
-      }
-      if (*First == 'z') {
-        ++First;
-        Node *Ex = getDerived().parseExpr();
-        if (!Ex)
-          return nullptr;
-        return make<CallExpr>(Name, makeNodeArray(&Ex, &Ex + 1));
+      if (consumeIf('t')) {
+        UUID = getDerived().parseType();
+        IsUUID = true;
+      } else if (consumeIf('z')) {
+        UUID = getDerived().parseExpr();
+        IsUUID = true;
       }
     }
     size_t ExprsBegin = Names.size();
+    if (IsUUID) {
+      if (UUID == nullptr)
+        return nullptr;
+      Names.push_back(UUID);
+    } else {
       while (!consumeIf('E')) {
         Node *E = getDerived().parseTemplateArg();
         if (E == nullptr)
           return E;
         Names.push_back(E);
       }
+    }
     return make<CallExpr>(Name, popTrailingNodeArray(ExprsBegin));
   }
   case '1':
   case '2':
   case '3':
   case '4':
   case '5':
   case '6':

llvm/include/llvm/Demangle/ItaniumDemangle.h

case 'u': {
     Node *Name = getDerived().parseSourceName(/*NameState=*/nullptr);
     if (!Name)
       return nullptr;
     // Special case legacy __uuidof mangling. The 't' and 'z' appear where the
     // standard encoding expects a <template-arg>, and would be otherwise be
     // interpreted as <type> node 'short' or 'ellipsis'. However, neither
     // __uuidof(short) nor __uuidof(...) can actually appear, so there is no
     // actual conflict here.
+    bool IsUUID = false;
+    Node *UUID = nullptr;
     if (Name->getBaseName() == "__uuidof") {
-      if (numLeft() < 2)
-        return nullptr;
-      if (*First == 't') {
-        ++First;
-        Node *Ty = getDerived().parseType();
-        if (!Ty)
-          return nullptr;
-        return make<CallExpr>(Name, makeNodeArray(&Ty, &Ty + 1));
-      }
-      if (*First == 'z') {
-        ++First;
-        Node *Ex = getDerived().parseExpr();
-        if (!Ex)
-          return nullptr;
-        return make<CallExpr>(Name, makeNodeArray(&Ex, &Ex + 1));
+      if (consumeIf('t')) {
+        UUID = getDerived().parseType();
+        IsUUID = true;
+      } else if (consumeIf('z')) {
+        UUID = getDerived().parseExpr();
+        IsUUID = true;
       }
     }
     size_t ExprsBegin = Names.size();
+    if (IsUUID) {
+      if (UUID == nullptr)
+        return nullptr;
+      Names.push_back(UUID);
+    } else {
       while (!consumeIf('E')) {
         Node *E = getDerived().parseTemplateArg();
         if (E == nullptr)
           return E;
         Names.push_back(E);
       }
+    }
     return make<CallExpr>(Name, popTrailingNodeArray(ExprsBegin));
   }
   case '1':
   case '2':
   case '3':
   case '4':
   case '5':
   case '6':