Add support for function attribute 'not_tail_called'.

This attribute is used to prevent tail-call optimizations to the marked
function. For example, in the following piece of code, foo1 will not be
tail-call optimized: 

int __attribute__((not_tail_called)) foo1(int);

int foo2(int a) {
  return foo1(a); // Tail-call optimization is not performed.
}

The attribute has effect only on statically bound calls. It has no
effect on indirect calls. Also, virtual functions and objective-c
methods cannot be marked as 'not_tail_called'.

rdar://problem/22667622

Differential Revision: http://reviews.llvm.org/D12922

llvm-svn: 252369

1 files changed, 10 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6297efb73a2..009fe16f948 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5373,6 +5373,16 @@ static void checkAttributesAfterMerging(Sema &S, NamedDecl &ND) {
       ND.setInvalidDecl();
     }
   }
+
+  // Virtual functions cannot be marked as 'notail'.
+  if (auto *Attr = ND.getAttr<NotTailCalledAttr>())
+    if (auto *MD = dyn_cast<CXXMethodDecl>(&ND))
+      if (MD->isVirtual()) {
+        S.Diag(ND.getLocation(),
+               diag::err_invalid_attribute_on_virtual_function)
+            << Attr;
+        ND.dropAttr<NotTailCalledAttr>();
+      }
 }
 
 static void checkDLLAttributeRedeclaration(Sema &S, NamedDecl *OldDecl,