[OpenCL] Diagnose redundant address space conversion

Add a warning if a parameter with a named address space is passed
to a to_addr builtin.

For example:

  int i;
  to_private(&i); // generate warning as conversion from private to private is redundant.

Patch by Alistair Davies.

Differential Revision: https://reviews.llvm.org/D51411

llvm-svn: 342638

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -8613,6 +8613,10 @@ def err_opencl_variadic_function : Error<
   "invalid prototype, variadic arguments are not allowed in OpenCL">;
 def err_opencl_requires_extension : Error<
   "use of %select{type|declaration}0 %1 requires %2 extension to be enabled">;
+def warn_opencl_generic_address_space_arg : Warning<
+  "passing non-generic address space pointer to %0"
+  " may cause dynamic conversion affecting performance">,
+  InGroup<Conversion>, DefaultIgnore;
 
 // OpenCL v2.0 s6.13.6 -- Builtin Pipe Functions
 def err_opencl_builtin_pipe_first_arg : Error<

clang/lib/Sema/SemaChecking.cpp

@@ -849,6 +849,13 @@ static bool SemaOpenCLBuiltinToAddr(Sema &S, unsigned BuiltinID,
     return true;
   }
 
+  if (RT->getPointeeType().getAddressSpace() != LangAS::opencl_generic) {
+    S.Diag(Call->getArg(0)->getBeginLoc(),
+           diag::warn_opencl_generic_address_space_arg)
+        << Call->getDirectCallee()->getNameInfo().getAsString()
+        << Call->getArg(0)->getSourceRange();
+  }
+
   RT = RT->getPointeeType();
   auto Qual = RT.getQualifiers();
   switch (BuiltinID) {

clang/test/SemaOpenCL/to_addr_builtin.cl

@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -verify -fsyntax-only %s
-// RUN: %clang_cc1 -verify -fsyntax-only -cl-std=CL2.0 %s
+// RUN: %clang_cc1 -Wconversion -verify -fsyntax-only -cl-std=CL2.0 %s
 
 void test(void) {
   global int *glob;
@@ -43,13 +43,15 @@ void test(void) {
   // expected-warning@-2{{incompatible integer to pointer conversion assigning to '__local int *' from 'int'}}
 #else
   // expected-error@-4{{assigning '__global int *' to '__local int *' changes address space of pointer}}
+  // expected-warning@-5{{passing non-generic address space pointer to to_global may cause dynamic conversion affecting performance}}
 #endif
 
   global char *glob_c = to_global(loc);
 #if __OPENCL_C_VERSION__ < CL_VERSION_2_0
   // expected-warning@-2{{incompatible integer to pointer conversion initializing '__global char *' with an expression of type 'int'}}
 #else
   // expected-warning@-4{{incompatible pointer types initializing '__global char *' with an expression of type '__global int *'}}
+  // expected-warning@-5{{passing non-generic address space pointer to to_global may cause dynamic conversion affecting performance}}
 #endif
 
 }