[TableGen] Avoid repeated hash lookups (NFC) (#123018)

Author: kazutakahirata

llvm/utils/TableGen/GlobalISelCombinerEmitter.cpp

@@ -2645,8 +2645,8 @@ GICombinerEmitter::buildMatchTable(MutableArrayRef<RuleMatcher> Rules) {
   for (RuleMatcher &Rule : Rules) {
     const StringRef Opcode = Rule.getOpcode();
     assert(!Opcode.empty() && "Didn't expect an undefined opcode");
-    if (OpcodeOrder.count(Opcode) == 0)
-      OpcodeOrder[Opcode] = CurrentOrdering++;
+    if (OpcodeOrder.try_emplace(Opcode, CurrentOrdering).second)
+      ++CurrentOrdering;
   }
 
   llvm::stable_sort(InputRules, [&OpcodeOrder](const Matcher *A,

llvm/utils/TableGen/GlobalISelEmitter.cpp

@@ -2216,8 +2216,8 @@ GlobalISelEmitter::buildMatchTable(MutableArrayRef<RuleMatcher> Rules,
   for (RuleMatcher &Rule : Rules) {
     const StringRef Opcode = Rule.getOpcode();
     assert(!Opcode.empty() && "Didn't expect an undefined opcode");
-    if (OpcodeOrder.count(Opcode) == 0)
-      OpcodeOrder[Opcode] = CurrentOrdering++;
+    if (OpcodeOrder.try_emplace(Opcode, CurrentOrdering).second)
+      ++CurrentOrdering;
   }
 
   llvm::stable_sort(