[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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@372294 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 40 insertions, 7 deletions

diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst
index 80c960909f..9826c41c35 100644
--- a/docs/LanguageExtensions.rst
+++ b/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**:
 
diff --git a/include/clang/Basic/Builtins.def b/include/clang/Basic/Builtins.def
index 6dd0d3a731..ef5614a53f 100644
--- a/include/clang/Basic/Builtins.def
+++ b/include/clang/Basic/Builtins.def
@@ -1470,7 +1470,7 @@ BUILTIN(__builtin_operator_new, "v*z", "tc")
 BUILTIN(__builtin_operator_delete, "vv*", "tn")
 BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
 BUILTIN(__builtin_dump_struct, "ivC*v*", "tn")
-BUILTIN(__builtin_preserve_access_index, "vC*vC*", "nU")
+BUILTIN(__builtin_preserve_access_index, "v.", "t")
 
 // Safestack builtins
 BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 8dd72d27e3..e72d1052dd 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -9925,4 +9925,7 @@ def err_bit_cast_non_trivially_copyable : Error<
   "__builtin_bit_cast %select{source|destination}0 type must be trivially copyable">;
 def err_bit_cast_type_size_mismatch : Error<
   "__builtin_bit_cast source size does not equal destination size (%0 vs %1)">;
+
+def err_builtin_preserve_access_index_invalid_arg : Error<
+  "__builtin_preserve_access_index argument must a pointer type instead of %0">;
 } // end of sema component.
diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index af69c231f1..4a3d26a5ab 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -191,12 +191,22 @@ static bool SemaBuiltinAddressof(Sema &S, CallExpr *TheCall) {
   return false;
 }
 
-/// Check the number of arguments, and set the result type to
+/// Check the number of arguments and arg type, and set the result type to
 /// the argument type.
 static bool SemaBuiltinPreserveAI(Sema &S, CallExpr *TheCall) {
   if (checkArgCount(S, TheCall, 1))
     return true;
 
+  // The argument type must be a pointer
+  ExprResult Arg = TheCall->getArg(0);
+  QualType Ty = Arg.get()->getType();
+  if (!Ty->isPointerType()) {
+    S.Diag(Arg.get()->getBeginLoc(),
+           diag::err_builtin_preserve_access_index_invalid_arg)
+        << Ty << Arg.get()->getSourceRange();
+    return true;
+  }
+
   TheCall->setType(TheCall->getArg(0)->getType());
   return false;
 }
diff --git a/test/Sema/builtin-preserve-access-index.c b/test/Sema/builtin-preserve-access-index.c
index c10ceb5145..71da8457fa 100644
--- a/test/Sema/builtin-preserve-access-index.c
+++ b/test/Sema/builtin-preserve-access-index.c
@@ -4,10 +4,28 @@ const void *invalid1(const int *arg) {
   return __builtin_preserve_access_index(&arg[1], 1); // expected-error {{too many arguments to function call, expected 1, have 2}}
 }
 
-void *invalid2(const int *arg) {
-  return __builtin_preserve_access_index(&arg[1]); // expected-warning {{returning 'const void *' from a function with result type 'void *' discards qualifiers}}
+const void *invalid2(const int *arg) {
+  return __builtin_preserve_access_index(1); // expected-error {{__builtin_preserve_access_index argument must a pointer type instead of 'int'}}
 }
 
-const void *invalid3(const int *arg) {
-  return __builtin_preserve_access_index(1); // expected-warning {{incompatible integer to pointer conversion passing 'int' to parameter of type 'const void *'}}
+void *invalid3(const int *arg) {
+  return __builtin_preserve_access_index(&arg[1]); // expected-warning {{returning 'const int *' from a function with result type 'void *' discards qualifiers}}
+}
+
+const void *invalid4(volatile const int *arg) {
+  return __builtin_preserve_access_index(arg); // expected-warning {{returning 'const volatile int *' from a function with result type 'const void *' discards qualifiers}}
+}
+
+int *valid5(int *arg) {
+  return __builtin_preserve_access_index(arg);
+}
+
+int valid6(const volatile int *arg) {
+  return *__builtin_preserve_access_index(arg);
+}
+
+struct s { int a; int b; };
+
+int valid7(struct s *arg) {
+  return *__builtin_preserve_access_index(&arg->b);
 }