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, 17 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/attr-notail.cpp b/clang/test/CodeGenCXX/attr-notail.cpp
new file mode 100644
index 00000000000..80af424ff3e
--- /dev/null
+++ b/clang/test/CodeGenCXX/attr-notail.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple=x86_64-apple-darwin -std=c++11 -emit-llvm -o - %s | FileCheck %s
+
+class Class1 {
+public:
+  [[clang::not_tail_called]] int m1();
+  int m2();
+};
+
+int foo1(int a, Class1 *c1) {
+  if (a)
+    return c1->m1();
+  return c1->m2();
+}
+
+// CHECK-LABEL: define i32 @_Z4foo1iP6Class1(
+// CHECK: %{{[a-z0-9]+}} = notail call i32 @_ZN6Class12m1Ev(%class.Class1*
+// CHECK: %{{[a-z0-9]+}} = call i32 @_ZN6Class12m2Ev(%class.Class1*