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, 15 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 6d9d7d4aaab..5b85bf0da2c 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1701,6 +1701,15 @@ static void handleDependencyAttr(Sema &S, Scope *Scope, Decl *D,
                                    Attr.getAttributeSpellingListIndex()));
 }
 
+static void handleNotTailCalledAttr(Sema &S, Decl *D,
+                                    const AttributeList &Attr) {
+  if (checkAttrMutualExclusion<AlwaysInlineAttr>(S, D, Attr))
+    return;
+
+  D->addAttr(::new (S.Context) NotTailCalledAttr(
+      Attr.getRange(), S.Context, Attr.getAttributeSpellingListIndex()));
+}
+
 static void handleUsedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
     if (VD->hasLocalStorage()) {
@@ -3419,6 +3428,9 @@ OptimizeNoneAttr *Sema::mergeOptimizeNoneAttr(Decl *D, SourceRange Range,
 
 static void handleAlwaysInlineAttr(Sema &S, Decl *D,
                                    const AttributeList &Attr) {
+  if (checkAttrMutualExclusion<NotTailCalledAttr>(S, D, Attr))
+    return;
+
   if (AlwaysInlineAttr *Inline = S.mergeAlwaysInlineAttr(
           D, Attr.getRange(), Attr.getName(),
           Attr.getAttributeSpellingListIndex()))
@@ -4991,6 +5003,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_ReturnsTwice:
     handleSimpleAttribute<ReturnsTwiceAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_NotTailCalled:
+    handleNotTailCalledAttr(S, D, Attr);
+    break;
   case AttributeList::AT_Used:
     handleUsedAttr(S, D, Attr);
     break;