[CFG] [analyzer] Disable argument construction contexts for variadic …

…functions.

The analyzer doesn't make use of them anyway and they seem to have
pretty weird AST from time to time, so let's just skip them for now.

Fixes pr37769.

Differential Revision: https://reviews.llvm.org/D50824

llvm-svn: 340975

clang/lib/Analysis/CFG.cpp

@@ -2421,8 +2421,6 @@ CFGBlock *CFGBuilder::VisitCallExpr(CallExpr *C, AddStmtChoice asc) {
     if (!boundType.isNull()) calleeType = boundType;
   }
 
-  findConstructionContextsForArguments(C);
-
   // If this is a call to a no-return function, this stops the block here.
   bool NoReturn = getFunctionExtInfo(*calleeType).getNoReturn();
 
@@ -2439,6 +2437,13 @@ CFGBlock *CFGBuilder::VisitCallExpr(CallExpr *C, AddStmtChoice asc) {
   bool OmitArguments = false;
 
   if (FunctionDecl *FD = C->getDirectCallee()) {
+    // TODO: Support construction contexts for variadic function arguments.
+    // These are a bit problematic and not very useful because passing
+    // C++ objects as C-style variadic arguments doesn't work in general
+    // (see [expr.call]).
+    if (!FD->isVariadic())
+      findConstructionContextsForArguments(C);
+
     if (FD->isNoReturn() || C->isBuiltinAssumeFalse(*Context))
       NoReturn = true;
     if (FD->hasAttr<NoThrowAttr>())

clang/test/Analysis/cfg-rich-constructors.cpp

@@ -1028,3 +1028,18 @@ void testOperators() {
   C(1) + C(2);
 }
 } // namespace operators
+
+namespace variadic_function_arguments {
+class C {
+ public:
+  C(int);
+};
+
+int variadic(...);
+
+// This code is quite exotic, so let's not test the CFG for it,
+// but only make sure we don't crash.
+void testCrashOnVariadicArgument() {
+  C c(variadic(0 ? c : 0)); // no-crash
+}
+} // namespace variadic_function_arguments