[analyzer] pr34766: Fix a crash on explicit construction of std::initializer_list.

[NoQ]

Summary

std::initializer_list objects can be constructed sort of explicitly, eg. (std::initializer_list<int>){12}. This produces an AST that looks like

CompoundLiteralExpr 0x11987f1a0 'std::initializer_list<int>':'class std::initializer_list<int>'
`-CXXStdInitializerListExpr 0x11987f188 'std::initializer_list<int>':'class std::initializer_list<int>'
  `-MaterializeTemporaryExpr 0x11987f170 'const int [1]' xvalue
    `-InitListExpr 0x11987f128 'const int [1]'
      `-IntegerLiteral 0x11987cd18 'int' 12

We crash because we did not expect to see CompoundLiteralExpr containing CXXStdInitializerListExpr.

It seems correct to pass the value through CompoundLiteralExpr transparently (the value is currently a conjured structure-symbol of initializer_list type, which sounds like a correct value for the expression, even if not super verbose), hence the patch.

[george.karpenkov]

I think I lack context to completely get what is going on here: I assume we don't model the assignment here?

lib/StaticAnalyzer/Core/ExprEngineC.cpp

533

Empty "if" looks weird, why not just negate the condition, and then you could get rid of "else"?

[NoQ]

In D39803#919945, @george.karpenkov wrote:

I think I lack context to completely get what is going on here: I assume we don't model the assignment here?

• We model IntegralLiteral as nonloc::ConcreteInt 12 S32b.
• We model InitListExpr as nonloc::CompoundVal { 12 S32b }.
• We model MaterializeTemporaryExpr as loc::MemRegionVal &temp_object{const int [1], {12}} in which {12 S32b} is stored, retroactively creating the location in which the list was supposed to be present from the start (TODO: why not CompoundLiteralRegion?).
• We do not model CXXStdInitializerListExpr or internals of std::initializer_list, hence the value of this expresssion, conservatively, is conj_$0{std::initializer_list<int>}. See also D35216.
• We now model CompoundLiteralExpr as conj_$0{std::initializer_list<int>} as no-op.

[dcoughlin]

LGTM.

[xazax.hun]

LGTM!

[alexfh]

Is anything holding this patch?

lib/StaticAnalyzer/Core/ExprEngineC.cpp

void ExprEngine::VisitCompoundLiteralExpr(const CompoundLiteralExpr *CL,
   StmtNodeBuilder B(Pred, Dst, *currBldrCtx);
 
   ProgramStateRef State = Pred->getState();
   const LocationContext *LCtx = Pred->getLocationContext();
 
   const Expr *Init = CL->getInitializer();
   SVal V = State->getSVal(CL->getInitializer(), LCtx);
 
-  if (isa<CXXConstructExpr>(Init)) {
+  if (isa<CXXConstructExpr>(Init) || isa<CXXStdInitializerListExpr>(Init)) {
     // No work needed. Just pass the value up to this expression.
   } else {
     assert(isa<InitListExpr>(Init));
     Loc CLLoc = State->getLValue(CL, LCtx);
     State = State->bindLoc(CLLoc, V, LCtx);
 
     if (CL->isGLValue())
       V = CLLoc;

test/Analysis/initializer.cpp

struct C {
    const char(&f)[2];
 };
 }
 
 namespace CXX_initializer_lists {
 struct C {
   C(std::initializer_list<int *> list);
 };
-void foo() {
+void testPointerEscapeIntoLists() {
   C empty{}; // no-crash
 
   // Do not warn that 'x' leaks. It might have been deleted by
   // the destructor of 'c'.
   int *x = new int;
   C c{x}; // no-warning
 }
+
+void testPassListsWithExplicitConstructors() {
+  (void)(std::initializer_list<int>){12}; // no-crash
+}
 }