[CLANG][BPF] change __builtin_preserve_access_index() signature

The clang intrinsic __builtin_preserve_access_index() currently
has signature:
  const void * __builtin_preserve_access_index(const void * ptr)

This may cause compiler warning when:
  - parameter type is "volatile void *" or "const volatile void *", or
  - the assign-to type of the intrinsic does not have "const" qualifier.
Further, this signature does not allow dereference of the
builtin result pointer as it is a "const void *" type, which
adds extra step for the user to do type casting.

Let us change the signature to:
  PointerT __builtin_preserve_access_index(PointerT ptr)
such that the result and argument types are the same.
With this, directly dereferencing the builtin return value
becomes possible.

Differential Revision: https://reviews.llvm.org/D67734

llvm-svn: 372294

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index 80c960909f7..9826c41c358 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -2353,12 +2353,14 @@ and other similar allocation libraries, and are only available in C++.
 array subscript access and structure/union member access are relocatable
 under bpf compile-once run-everywhere framework. Debuginfo (typically
 with ``-g``) is needed, otherwise, the compiler will exit with an error.
+The return type for the intrinsic is the same as the type of the
+argument, and must be a pointer type.
 
 **Syntax**:
 
 .. code-block:: c
 
-  const void * __builtin_preserve_access_index(const void * ptr)
+  PointerT __builtin_preserve_access_index(PointerT ptr)
 
 **Example of Use**: