[Sema] Fix a crash on variadic enable_if functions.

Currently, when trying to evaluate an enable_if condition, we try to
evaluate all arguments a user passes to a function. Given that we can't
use variadic arguments from said condition anyway, not converting them
is a reasonable thing to do. So, this patch makes us ignore any varargs
when attempting to check an enable_if condition.

We'd crash because, in order to convert an argument, we need its
ParmVarDecl. Variadic arguments don't have ParmVarDecls.

llvm-svn: 278471

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 04751d21bfa..ad95a5ca46f 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -5974,8 +5974,12 @@ EnableIfAttr *Sema::CheckEnableIf(FunctionDecl *Function, ArrayRef<Expr *> Args,
   SmallVector<Expr *, 16> ConvertedArgs;
   bool InitializationFailed = false;
 
+  // Ignore any variadic parameters. Converting them is pointless, since the
+  // user can't refer to them in the enable_if condition.
+  unsigned ArgSizeNoVarargs = std::min(Function->param_size(), Args.size());
+
   // Convert the arguments.
-  for (unsigned I = 0, E = Args.size(); I != E; ++I) {
+  for (unsigned I = 0; I != ArgSizeNoVarargs; ++I) {
     ExprResult R;
     if (I == 0 && !MissingImplicitThis && isa<CXXMethodDecl>(Function) &&
         !cast<CXXMethodDecl>(Function)->isStatic() &&