[mlir] omit extra newlines if there are no aliases

[matthiaskramm]

Summary

We used to always print an extra newline after every kindAlias
group, even if the groups were empty. This is now omitted. In
particular, an empty module is now printed as "module {\n}", not
"\n\nmodule {\n}".

[rriddle]

mlir/lib/IR/AsmPrinter.cpp

388

nit:

if (aliasAttrsPair.second.empty())
  continue;

[matthiaskramm]

Use 'continue' instead of 'if'.

mlir/lib/IR/AsmPrinter.cpp

auto printAlias = [&](StringRef alias, Attribute attr, int index) {
     if (index != NonAttrKindAlias)
       os << index;
     os << " = " << attr << newLine;
   };
 
   // Print all of the attribute kind aliases.
   for (auto &kindAlias : attrKindToAlias) {
     auto &aliasAttrsPair = kindAlias.second;
-    for (unsigned i = 0, e = aliasAttrsPair.second.size(); i != e; ++i)
+    if (aliasAttrsPair.second.empty())
+      continue;
+    for (unsigned i = 0; i != aliasAttrsPair.second.size(); ++i)
       printAlias(aliasAttrsPair.first, aliasAttrsPair.second[i], i);
     os << newLine;
   }
 
   // In a second pass print all of the remaining attribute aliases that aren't
   // kind aliases.
   for (Attribute attr : usedAttributes) {
     auto alias = attrToAlias.find(attr);
     if (alias != attrToAlias.end() && alias->second.second == NonAttrKindAlias)
       printAlias(alias->second.first, attr, alias->second.second);