[mlir] Use *Map::try_emplace (NFC) (#143341)

- try_emplace(Key) is shorter than insert({Key, nullptr}).
- try_emplace performs value initialization without value parameters.
- We overwrite values on successful insertion anyway.

Author: kazutakahirata

mlir/include/mlir/Debug/BreakpointManagers/TagBreakpointManager.h

@@ -48,7 +48,7 @@ class TagBreakpointManager
   /// If a breakpoint already exists for the given tag, return the existing
   /// instance.
   TagBreakpoint *addBreakpoint(StringRef tag) {
-    auto result = breakpoints.insert({tag, nullptr});
+    auto result = breakpoints.try_emplace(tag);
     auto &it = result.first;
     if (result.second)
       it->second = std::make_unique<TagBreakpoint>(tag.str());

mlir/lib/Bytecode/Writer/IRNumbering.cpp

@@ -308,7 +308,7 @@ void IRNumberingState::computeGlobalNumberingState(Operation *rootOp) {
 }
 
 void IRNumberingState::number(Attribute attr) {
-  auto it = attrs.insert({attr, nullptr});
+  auto it = attrs.try_emplace(attr);
   if (!it.second) {
     ++it.first->second->refCount;
     return;
@@ -475,7 +475,7 @@ void IRNumberingState::number(OperationName opName) {
 }
 
 void IRNumberingState::number(Type type) {
-  auto it = types.insert({type, nullptr});
+  auto it = types.try_emplace(type);
   if (!it.second) {
     ++it.first->second->refCount;
     return;

mlir/lib/IR/MLIRContext.cpp

@@ -810,7 +810,7 @@ OperationName::OperationName(StringRef name, MLIRContext *context) {
   // Acquire a writer-lock so that we can safely create the new instance.
   ScopedWriterLock lock(ctxImpl.operationInfoMutex, isMultithreadingEnabled);
 
-  auto it = ctxImpl.operations.insert({name, nullptr});
+  auto it = ctxImpl.operations.try_emplace(name);
   if (it.second) {
     auto nameAttr = StringAttr::get(context, name);
     it.first->second = std::make_unique<UnregisteredOpModel>(

mlir/lib/Target/LLVMIR/LoopAnnotationTranslation.cpp

@@ -280,7 +280,7 @@ LoopAnnotationTranslation::translateLoopAnnotation(LoopAnnotationAttr attr,
 llvm::MDNode *
 LoopAnnotationTranslation::getAccessGroup(AccessGroupAttr accessGroupAttr) {
   auto [result, inserted] =
-      accessGroupMetadataMapping.insert({accessGroupAttr, nullptr});
+      accessGroupMetadataMapping.try_emplace(accessGroupAttr);
   if (inserted)
     result->second = llvm::MDNode::getDistinct(llvmModule.getContext(), {});
   return result->second;

mlir/lib/Transforms/Utils/CFGToSCF.cpp

@@ -427,8 +427,7 @@ class ReturnLikeExitCombiner {
   /// region with an instance of `returnLikeOp`s kind.
   void combineExit(Operation *returnLikeOp,
                    function_ref<Value(unsigned)> getSwitchValue) {
-    auto [iter, inserted] =
-        returnLikeToCombinedExit.insert({returnLikeOp, nullptr});
+    auto [iter, inserted] = returnLikeToCombinedExit.try_emplace(returnLikeOp);
     if (!inserted && iter->first == returnLikeOp)
       return;
 
@@ -1284,7 +1283,7 @@ FailureOr<bool> mlir::transformCFGToSCF(Region &region,
 
   DenseMap<Type, Value> typedUndefCache;
   auto getUndefValue = [&](Type type) {
-    auto [iter, inserted] = typedUndefCache.insert({type, nullptr});
+    auto [iter, inserted] = typedUndefCache.try_emplace(type);
     if (!inserted)
       return iter->second;
 

mlir/lib/Transforms/Utils/Inliner.cpp

@@ -45,7 +45,7 @@ static void walkReferencedSymbolNodes(
 
   Operation *symbolTableOp = op->getParentOp();
   for (const SymbolTable::SymbolUse &use : *symbolUses) {
-    auto refIt = resolvedRefs.insert({use.getSymbolRef(), nullptr});
+    auto refIt = resolvedRefs.try_emplace(use.getSymbolRef());
     CallGraphNode *&node = refIt.first->second;
 
     // If this is the first instance of this reference, try to resolve a