[CodeGen] Avoid repeated hash lookups (NFC) (#111274)

Author: kazutakahirata

llvm/lib/CodeGen/RegisterBankInfo.cpp

@@ -103,12 +103,10 @@ const TargetRegisterClass *
 RegisterBankInfo::getMinimalPhysRegClass(Register Reg,
                                          const TargetRegisterInfo &TRI) const {
   assert(Reg.isPhysical() && "Reg must be a physreg");
-  const auto &RegRCIt = PhysRegMinimalRCs.find(Reg);
-  if (RegRCIt != PhysRegMinimalRCs.end())
-    return RegRCIt->second;
-  const TargetRegisterClass *PhysRC = TRI.getMinimalPhysRegClassLLT(Reg, LLT());
-  PhysRegMinimalRCs[Reg] = PhysRC;
-  return PhysRC;
+  const auto [RegRCIt, Inserted] = PhysRegMinimalRCs.try_emplace(Reg);
+  if (Inserted)
+    RegRCIt->second = TRI.getMinimalPhysRegClassLLT(Reg, LLT());
+  return RegRCIt->second;
 }
 
 const RegisterBank *RegisterBankInfo::getRegBankFromConstraints(