[analyzer] Fix a false memory leak reports involving placement new

clang/lib/StaticAnalyzer/Checkers/MallocChecker.cpp

@@ -1371,6 +1371,20 @@ void MallocChecker::checkIfFreeNameIndex(ProgramStateRef State,
   C.addTransition(State);
 }
 
+const Expr *getPlacementNewBufferArg(const CallExpr *CE,
+                                     const FunctionDecl *FD) {
+  // Checking for signature:
+  // void* operator new  ( std::size_t count, void* ptr );
+  // void* operator new[]( std::size_t count, void* ptr );
+  if (CE->getNumArgs() != 2 || (FD->getOverloadedOperator() != OO_New &&
+                                FD->getOverloadedOperator() != OO_Array_New))
+    return nullptr;
+  auto BuffType = FD->getParamDecl(1)->getType();
+  if (BuffType.isNull() || !BuffType->isVoidPointerType())
+    return nullptr;
+  return CE->getArg(1);
+}
+
 void MallocChecker::checkCXXNewOrCXXDelete(ProgramStateRef State,
                                            const CallEvent &Call,
                                            CheckerContext &C) const {
@@ -1386,6 +1400,14 @@ void MallocChecker::checkCXXNewOrCXXDelete(ProgramStateRef State,
   // processed by the checkPostStmt callbacks for CXXNewExpr and
   // CXXDeleteExpr.
   const FunctionDecl *FD = C.getCalleeDecl(CE);
+  if (const auto *BufArg = getPlacementNewBufferArg(CE, FD)) {
+    // Placement new does not allocate memory
+    auto RetVal = State->getSVal(BufArg, Call.getLocationContext());
+    State = State->BindExpr(CE, C.getLocationContext(), RetVal);
+    C.addTransition(State);
+    return;
+  }
+
   switch (FD->getOverloadedOperator()) {
   case OO_New:
     State = MallocMemAux(C, Call, CE->getArg(0), UndefinedVal(), State,

clang/test/Analysis/NewDelete-checker-test.cpp

@@ -26,9 +26,10 @@
 // RUN:   -analyzer-checker=cplusplus.NewDeleteLeaks
 //
 // RUN: %clang_analyze_cc1 -std=c++17 -fblocks -verify %s \
-// RUN:   -verify=expected,leak \
+// RUN:   -verify=expected,leak,inspection \
 // RUN:   -analyzer-checker=core \
-// RUN:   -analyzer-checker=cplusplus.NewDeleteLeaks
+// RUN:   -analyzer-checker=cplusplus.NewDeleteLeaks \
+// RUN:   -analyzer-checker=debug.ExprInspection
 
 #include "Inputs/system-header-simulator-cxx.h"
 
@@ -63,6 +64,39 @@ void testGlobalNoThrowPlacementExprNewBeforeOverload() {
   int *p = new(std::nothrow) int;
 } // leak-warning{{Potential leak of memory pointed to by 'p'}}
 
+//----- Standard pointer placement operators
+void testGlobalPointerPlacementNew() {
+  int i;
+  void *p1 = operator new(0, &i); // no leak: placement new never allocates
+  void *p2 = operator new[](0, &i); // no leak
+  int *p3 = new(&i) int; // no leak
+  int *p4 = new(&i) int[0]; // no leak
+}
+
+template<typename T>
+void clang_analyzer_dump(T x);
+
+void testPlacementNewBufValue() {
+  int i = 10;
+  int *p = new(&i) int;
+  clang_analyzer_dump(p); // inspection-warning{{&i}}
+  clang_analyzer_dump(*p); // inspection-warning{{10}}
+}
+
+void testPlacementNewBufValueExplicitOp() {
+  int i = 10;
+  int *p = (int*)operator new(sizeof(int), &i);
+  clang_analyzer_dump(p); // inspection-warning{{&i}}
+  clang_analyzer_dump(*p); // inspection-warning{{10}}
+}
+
+void testPlacementArrNewBufValueExplicitArrOp() {
+  int i = 10;
+  int *p = (int*)operator new[](sizeof(int), &i);
+  clang_analyzer_dump(p); // inspection-warning{{&i}}
+  clang_analyzer_dump(*p); // inspection-warning{{10}}
+}
+
 //----- Other cases
 void testNewMemoryIsInHeap() {
   int *p = new int;