[TableGen] Avoid repeated hash lookups (NFC) (#123161)

Author: kazutakahirata

llvm/utils/TableGen/Common/GlobalISel/GlobalISelMatchTable.cpp

@@ -875,10 +875,8 @@ unsigned RuleMatcher::getInsnVarID(InstructionMatcher &InsnMatcher) const {
 }
 
 void RuleMatcher::defineOperand(StringRef SymbolicName, OperandMatcher &OM) {
-  if (!DefinedOperands.contains(SymbolicName)) {
-    DefinedOperands[SymbolicName] = &OM;
+  if (DefinedOperands.try_emplace(SymbolicName, &OM).second)
     return;
-  }
 
   // If the operand is already defined, then we must ensure both references in
   // the matcher have the exact same node.
@@ -889,8 +887,7 @@ void RuleMatcher::defineOperand(StringRef SymbolicName, OperandMatcher &OM) {
 }
 
 void RuleMatcher::definePhysRegOperand(const Record *Reg, OperandMatcher &OM) {
-  if (!PhysRegOperands.contains(Reg))
-    PhysRegOperands[Reg] = &OM;
+  PhysRegOperands.try_emplace(Reg, &OM);
 }
 
 InstructionMatcher &