[SYCL] Fix function pointer address space (#5924)

Commits 57fd86d (https://reviews.llvm.org/D77119) and
4eaf584 (https://reviews.llvm.org/D111566) set
address space of function pointers unconditionally to program
address space.

A follow-up commit ed5b42b (https://reviews.llvm.org/D119045)
modified the code to retain explicitly specified address spaces
for function pointer. This introduced a regression in cases where
function pointers were captured as kernel arguments, since openCL
kernel generation sets global address space explicitly to all
pointers. This patch reverts the behavior for function pointers
captured as kernel arguments.

Signed-off-by: Elizabeth Andrews <[email protected]>

Author: elizabethandrews

clang/lib/Sema/SemaSYCL.cpp

@@ -2122,15 +2122,18 @@ class SyclKernelDeclCreator : public SyclKernelFieldHandler {
 
   bool handlePointerType(FieldDecl *FD, QualType FieldTy) final {
     // USM allows to use raw pointers instead of buffers/accessors, but these
-    // pointers point to the specially allocated memory. For pointer fields we
-    // add a kernel argument with the same type as field but global address
-    // space, because OpenCL requires it.
+    // pointers point to the specially allocated memory. For pointer fields,
+    // except for function pointer fields, we add a kernel argument with the
+    // same type as field but global address space, because OpenCL requires it.
+    // Function pointers should have program address space. This is set in
+    // CodeGen.
     QualType PointeeTy = FieldTy->getPointeeType();
     Qualifiers Quals = PointeeTy.getQualifiers();
     auto AS = Quals.getAddressSpace();
     // Leave global_device and global_host address spaces as is to help FPGA
     // device in memory allocations
-    if (AS != LangAS::sycl_global_device && AS != LangAS::sycl_global_host)
+    if (!PointeeTy->isFunctionType() && AS != LangAS::sycl_global_device &&
+        AS != LangAS::sycl_global_host)
       Quals.setAddressSpace(LangAS::sycl_global);
     PointeeTy = SemaRef.getASTContext().getQualifiedType(
         PointeeTy.getUnqualifiedType(), Quals);

clang/test/CodeGenSYCL/functionptr-addrspace.cpp

@@ -21,5 +21,16 @@ int main() {
     invoke_function(r, &a);
     invoke_function(f, &a);
   });
+
+  // Test function pointer as kernel argument. Function pointers should have program address space i.e. 0.
+
+  int (*fptr)();
+  int *ptr;
+
+  // define dso_local spir_kernel void @{{.*}}fake_kernel_2{{.*}}(i32 ()* align 4 %_arg_fptr, i32 addrspace(1)* align 4 %_arg_ptr)
+  kernel_single_task<class fake_kernel_2>([=]() {
+    invoke_function(fptr, ptr);
+  });
+
   return 0;
 }