[GlobalISel] Avoid repeated hash lookups (NFC) (#124393)

Author: kazutakahirata

llvm/lib/CodeGen/GlobalISel/CSEInfo.cpp

@@ -181,10 +181,7 @@ MachineInstr *GISelCSEInfo::getMachineInstrIfExists(FoldingSetNodeID &ID,
 
 void GISelCSEInfo::countOpcodeHit(unsigned Opc) {
 #ifndef NDEBUG
-  if (OpcodeHitTable.count(Opc))
-    OpcodeHitTable[Opc] += 1;
-  else
-    OpcodeHitTable[Opc] = 1;
+  ++OpcodeHitTable[Opc];
 #endif
   // Else do nothing.
 }