[flang] Consider bind(c) when lowering calls to intrinsic module procedures (#70386)

When attempting to lower an intrinsic module procedure call, take into
account bind(c). Such procedures cannot be lowered as intrinsics since
their implementation is external to the module.

With this solution, the hardcoded "omp_lib" string can be removed when
checking if intrinsic module procedure since all procedure interfaces in
that module use bind(c).

Author: razvanlupusoru

flang/lib/Lower/ConvertCall.cpp

@@ -2122,7 +2122,12 @@ genProcedureRef(CallContext &callContext) {
   mlir::Location loc = callContext.loc;
   if (auto *intrinsic = callContext.procRef.proc().GetSpecificIntrinsic())
     return genIntrinsicRef(intrinsic, callContext);
-  if (Fortran::lower::isIntrinsicModuleProcRef(callContext.procRef))
+  // If it is an intrinsic module procedure reference - then treat as
+  // intrinsic unless it is bind(c) (since implementation is external from
+  // module).
+  if (Fortran::lower::isIntrinsicModuleProcRef(callContext.procRef) &&
+      !Fortran::semantics::IsBindCProcedure(
+          *callContext.procRef.proc().GetSymbol()))
     return genIntrinsicRef(nullptr, callContext);
 
   if (callContext.isStatementFunctionCall())
@@ -2227,8 +2232,7 @@ bool Fortran::lower::isIntrinsicModuleProcRef(
     return false;
   const Fortran::semantics::Symbol *module =
       symbol->GetUltimate().owner().GetSymbol();
-  return module && module->attrs().test(Fortran::semantics::Attr::INTRINSIC) &&
-         module->name().ToString().find("omp_lib") == std::string::npos;
+  return module && module->attrs().test(Fortran::semantics::Attr::INTRINSIC);
 }
 
 std::optional<hlfir::EntityWithAttributes> Fortran::lower::convertCallToHLFIR(

flang/module/omp_lib.h

@@ -90,7 +90,7 @@
     omp_atv_blocked = 17, &
     omp_atv_interleaved = 18
 
-  type :: omp_alloctrait
+  type, bind(c) :: omp_alloctrait
     integer(kind=omp_alloctrait_key_kind) :: key, value
   end type omp_alloctrait
 
@@ -264,23 +264,23 @@
       integer(kind=omp_integer_kind), intent(out) :: place_nums(*)
     end subroutine omp_get_partition_place_nums
 
-    subroutine omp_set_affinity_format(format)
+    subroutine omp_set_affinity_format(format) bind(c)
       import
       character(len=*), intent(in) :: format
     end subroutine omp_set_affinity_format
 
-    function omp_get_affinity_format(buffer)
+    function omp_get_affinity_format(buffer) bind(c)
       import
       character(len=*), intent(out) :: buffer
       integer(kind=omp_integer_kind) :: omp_get_affinity_format
     end function omp_get_affinity_format
 
-    subroutine omp_display_affinity(format)
+    subroutine omp_display_affinity(format) bind(c)
       import
       character(len=*), intent(in) :: format
     end subroutine omp_display_affinity
 
-    function omp_capture_affinity(buffer, format)
+    function omp_capture_affinity(buffer, format) bind(c)
       import
       character(len=*), intent(out) :: buffer
       character(len=*), intent(in) :: format
@@ -339,7 +339,7 @@
       integer(kind=omp_integer_kind) :: omp_pause_resource
     end function omp_pause_resource
 
-    function omp_pause_resource_all(kind)
+    function omp_pause_resource_all(kind) bind(c)
       import
       integer(kind=omp_pause_resource_kind), value :: kind
       integer(kind=omp_integer_kind) :: omp_pause_resource_all
@@ -428,7 +428,7 @@
 ! Device Memory Routines
 
 ! Memory Management Routines
-    function omp_init_allocator(memspace, ntraits, traits)
+    function omp_init_allocator(memspace, ntraits, traits) bind(c)
       import
       integer(kind=omp_memspace_handle_kind), value :: memspace
       integer, value :: ntraits
@@ -446,7 +446,7 @@
       integer(kind=omp_allocator_handle_kind), value :: allocator
     end subroutine omp_set_default_allocator
 
-    function omp_get_default_allocator()
+    function omp_get_default_allocator() bind(c)
       import
       integer(kind=omp_allocator_handle_kind) :: omp_get_default_allocator
     end function omp_get_default_allocator

flang/test/Lower/OpenMP/omp-lib-num-threads.f90

@@ -0,0 +1,21 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - 2>&1 | FileCheck %s
+! RUN: bbc -fopenmp -emit-hlfir -o - %s 2>&1 | FileCheck %s
+!
+! Test that the calls to omp_lib's omp_get_num_threads and omp_set_num_threads
+! get lowered even though their implementation is not in the omp_lib module
+! (and this matters because this is an intrinsic module - and calls to
+! intrinsics are specially resolved).
+
+program main
+  use omp_lib
+  integer(omp_integer_kind) :: num_threads
+  integer(omp_integer_kind), parameter :: requested_num_threads = 4
+  call omp_set_num_threads(requested_num_threads)
+  num_threads = omp_get_num_threads()
+  print *, num_threads
+end program
+
+!CHECK-NOT: not yet implemented: intrinsic: omp_set_num_threads
+!CHECK-NOT: not yet implemented: intrinsic: omp_get_num_threads
+!CHECK: fir.call @omp_set_num_threads
+!CHECK: fir.call @omp_get_num_threads