[analyzer] Suppress escape of this-pointer during construction.

[NoQ]

Summary

This one's easy. Under -analyzer-config c++-allocator-inlining=true, since D41406, we've teached MallocChecker to use the new callback, check::NewAllocator, which fires between the end of the operator new() call and the beginning of the constructor call. Because the constructor call causes a pointer escape event, during which the pointer returned by operator new() immediately escapes, MallocChecker immediately loses track of the allocated symbol and becomes completely useless. In particular, NewDeleteLeaks suffers a lot.

I'm open to suggestions regarding whether we should suppress this sort of pointer escape on the checker side or globally.

[xazax.hun]

I am fine with suppressing the escape globally.
I did see some code in the wild where the constructors registered the objects with a (global) map.
But I think it is still easier to annotate code that does something unconventional than the other way around.

[a.sidorin]

Hi Artem,
I think that global suppression is fine. If one really wants to check such escapes, he can implement a separate callback for this.

[dcoughlin]

LGTM!

lib/StaticAnalyzer/Core/CallEvent.cpp

 SVal CXXConstructorCall::getCXXThisVal() const {
   if (Data)
     return loc::MemRegionVal(static_cast<const MemRegion *>(Data));
   return UnknownVal();
 }
 
 void CXXConstructorCall::getExtraInvalidatedValues(ValueList &Values,
                            RegionAndSymbolInvalidationTraits *ETraits) const {
-  if (Data)
-    Values.push_back(loc::MemRegionVal(static_cast<const MemRegion *>(Data)));
+  if (Data) {
+    loc::MemRegionVal MV(static_cast<const MemRegion *>(Data));
+    if (SymbolRef Sym = MV.getAsSymbol(true))
+      ETraits->setTrait(Sym,
+                        RegionAndSymbolInvalidationTraits::TK_SuppressEscape);
+    Values.push_back(MV);
+  }
 }
 
 void CXXConstructorCall::getInitialStackFrameContents(
                                              const StackFrameContext *CalleeCtx,
                                              BindingsTy &Bindings) const {
   AnyFunctionCall::getInitialStackFrameContents(CalleeCtx, Bindings);
 
   SVal ThisVal = getCXXThisVal();

test/Analysis/NewDeleteLeaks-PR19102.cpp

 // RUN: %clang_analyze_cc1 -analyzer-checker=core,cplusplus.NewDeleteLeaks -verify %s
+// RUN: %clang_analyze_cc1 -analyzer-checker=core,cplusplus.NewDeleteLeaks -analyzer-config c++-allocator-inlining=true -verify %s
 
 class A0 {};
 
 class A1 {
 public:
   A1(int);
 };