removed the redundant test file, update comments in placement-new.cpp test file to explain the removal of checker warning the rare case of allocating extra memory, and removed std::string explicit conversion operator

Author: Aethezz

clang/lib/StaticAnalyzer/Checkers/CheckPlacementNew.cpp

@@ -113,12 +113,11 @@ bool PlacementNewChecker::checkPlaceCapacityIsSufficient(
 
   if ((SizeOfPlaceCI->getValue() < SizeOfTargetCI->getValue())) {
     if (ExplodedNode *N = C.generateErrorNode(C.getState())) {
-      std::string Msg;
-      // TODO: use clang constant
-      Msg = std::string(
+      std::string Msg =
           llvm::formatv("Storage provided to placement new is only {0} bytes, "
                         "whereas the allocated type requires {1} bytes",
-                        SizeOfPlaceCI->getValue(), SizeOfTargetCI->getValue()));
+                        SizeOfPlaceCI->getValue(), SizeOfTargetCI->getValue());
+      // TODO: use clang constants
 
       auto R = std::make_unique<PathSensitiveBugReport>(SBT, Msg, N);
       bugreporter::trackExpressionValue(N, NE->getPlacementArg(0), *R);

clang/test/Analysis/placement-new.cpp

@@ -166,7 +166,8 @@ void f1() {
     short a;
   };
 
-  // bad (not enough space).
+  // on some systems, placement array new may allocate more memory than the nominal size of the array
+  // in such cases, test code could be problematic, but the checker doesn't warn here because this behavior is expected to be rare
   const unsigned N = 32;
   alignas(S) unsigned char buffer1[sizeof(S) * N]; 
   ::new (buffer1) S[N];                           
@@ -177,7 +178,8 @@ void f2() {
     short a;
   };
 
-  // maybe ok but we need to warn.
+  // on some systems, placement array new may allocate more memory than the nominal size of the array
+  // in such cases, test code could be problematic, but the checker doesn't warn here because this behavior is expected to be rare
   const unsigned N = 32;
   alignas(S) unsigned char buffer2[sizeof(S) * N + sizeof(int)]; 
   ::new (buffer2) S[N];