[DSE] Simpily if condition (NFC) (llvm#137777)

Note that the key-value pair has already been initialized, so assignment
is not necessary.

Author: NewSigma

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -1210,14 +1210,10 @@ struct DSEState {
   bool isInvisibleToCallerAfterRet(const Value *V) {
     if (isa<AllocaInst>(V))
       return true;
+
     auto I = InvisibleToCallerAfterRet.insert({V, false});
-    if (I.second) {
-      if (!isInvisibleToCallerOnUnwind(V)) {
-        I.first->second = false;
-      } else if (isNoAliasCall(V)) {
-        I.first->second = !PointerMayBeCaptured(V, /*ReturnCaptures=*/true);
-      }
-    }
+    if (I.second && isInvisibleToCallerOnUnwind(V) && isNoAliasCall(V))
+      I.first->second = !PointerMayBeCaptured(V, /*ReturnCaptures=*/true);
     return I.first->second;
   }