[mlir] Simplify calls to *Map::{insert,try_emplace} (NFC) (#143729)

This patch simplifies code by removing the values from
insert/try_emplace.  Note that default values inserted by try_emplace
are immediately overrideen in all these cases.

Author: kazutakahirata

mlir/lib/IR/AsmPrinter.cpp

@@ -1146,8 +1146,7 @@ template <typename T, typename... PrintArgs>
 std::pair<size_t, size_t> AliasInitializer::visitImpl(
     T value, llvm::MapVector<const void *, InProgressAliasInfo> &aliases,
     bool canBeDeferred, PrintArgs &&...printArgs) {
-  auto [it, inserted] =
-      aliases.insert({value.getAsOpaquePointer(), InProgressAliasInfo()});
+  auto [it, inserted] = aliases.try_emplace(value.getAsOpaquePointer());
   size_t aliasIndex = std::distance(aliases.begin(), it);
   if (!inserted) {
     // Make sure that the alias isn't deferred if we don't permit it.

mlir/lib/IR/SymbolTable.cpp

@@ -1100,7 +1100,7 @@ void SymbolUserMap::replaceAllUsesWith(Operation *symbol,
   if (newSymbol != symbol) {
     // Transfer over the users to the new symbol.  The reference to the old one
     // is fetched again as the iterator is invalidated during the insertion.
-    auto newIt = symbolToUsers.try_emplace(newSymbol, SetVector<Operation *>{});
+    auto newIt = symbolToUsers.try_emplace(newSymbol);
     auto oldIt = symbolToUsers.find(symbol);
     assert(oldIt != symbolToUsers.end() && "missing old users list");
     if (newIt.second)

mlir/lib/Transforms/Utils/CFGToSCF.cpp

@@ -709,7 +709,7 @@ transformToReduceLoop(Block *loopHeader, Block *exitBlock,
     llvm::SmallDenseMap<Block *, bool> dominanceCache;
     // Returns true if `loopBlock` dominates `block`.
     auto loopBlockDominates = [&](Block *block) {
-      auto [iter, inserted] = dominanceCache.insert({block, false});
+      auto [iter, inserted] = dominanceCache.try_emplace(block);
       if (!inserted)
         return iter->second;
       iter->second = dominanceInfo.dominates(loopBlock, block);