[analyzer] Support C++ default arguments if they are literal values.

A CXXDefaultArgExpr wraps an Expr owned by a ParmVarDecl belonging to the
called function. In general, ExprEngine and Environment ought to treat this
like a ParenExpr or other transparent wrapper expression, with the inside
expression evaluated first.

However, if we call the same function twice, we'd produce a CFG that contains
the same wrapped expression twice, and we're not set up to handle that. I've
added a FIXME to the CFG builder to come back to that, but meanwhile we can
at least handle expressions that don't need to be explicitly evaluated:
literals. This probably handles many common uses of default parameters:
true/false, null, etc.

Part of PR13385 / <rdar://problem/12156507>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162453 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
index 41d06f4546..70ea990f55 100644
--- a/lib/Analysis/CFG.cpp
+++ b/lib/Analysis/CFG.cpp
@@ -1022,6 +1022,14 @@ CFGBlock *CFGBuilder::Visit(Stmt * S, AddStmtChoice asc) {
     case Stmt::ExprWithCleanupsClass:
       return VisitExprWithCleanups(cast<ExprWithCleanups>(S), asc);
 
+    case Stmt::CXXDefaultArgExprClass:
+      // FIXME: The expression inside a CXXDefaultArgExpr is owned by the
+      // called function's declaration, not by the caller. If we simply add
+      // this expression to the CFG, we could end up with the same Expr
+      // appearing multiple times.
+      // PR13385 / <rdar://problem/12156507>
+      return VisitStmt(S, asc);
+
     case Stmt::CXXBindTemporaryExprClass:
       return VisitCXXBindTemporaryExpr(cast<CXXBindTemporaryExpr>(S), asc);