Add, and infer, a nofree function attribute

This patch adds a function attribute, nofree, to indicate that a function does
not, directly or indirectly, call a memory-deallocation function (e.g., free,
C++'s operator delete).

Reviewers: jdoerfert

Differential Revision: https://reviews.llvm.org/D49165

llvm-svn: 365336

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 8325e08e180..ae266629a64 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -1453,6 +1453,14 @@ example:
     duplicated by inlining. That implies that the function has
     internal linkage and only has one call site, so the original
     call is dead after inlining.
+``nofree``
+    This function attribute indicates that the function does not, directly or
+    indirectly, call a memory-deallocation function (free, for example). As a
+    result, uncaptured pointers that are known to be dereferenceable prior to a
+    call to a function with the ``nofree`` attribute are still known to be
+    dereferenceable after the call (the capturing condition is necessary in
+    environments where the function might communicate the pointer to another thread
+    which then deallocates the memory).
 ``noimplicitfloat``
     This attributes disables implicit floating-point instructions.
 ``noinline``