[Flang][OpenMP] Skip implicit mapping of named constants

[TIFitis]

Added early return when mapping named constants.

This prevents linking error in the following example:

program test
   use, intrinsic :: iso_c_binding, only: c_double
   implicit none

   real(c_double) :: x
   integer        :: i
   x = 0.0_c_double
   !$omp target teams distribute parallel do reduction(+:x)
   do i = 0, 9
      x = x + 1.0_c_double
   end do
   !$omp end target teams distribute parallel do
end program test

[Copilot]

Pull Request Overview

This PR addresses a linking error by skipping the implicit mapping of named constants in OpenMP target regions. The key changes include adding an early return for constants and updating the inline comment to explain the behavior.

Comments suppressed due to low confidence (1)

flang/lib/Lower/OpenMP/OpenMP.cpp:2398

• The comment mentions both parameters and constants, but the subsequent condition only checks for named constants. If parameters also require an early return, consider either updating the condition or adjusting the comment for clarity.

    // Skip parameters/constants as they do not need to be mapped.

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir

Author: Akash Banerjee (TIFitis)

Changes

Added early return when mapping named constants.

This prevents linking error in the following example:

program test
   use, intrinsic :: iso_c_binding, only: c_double
   implicit none

   real(c_double) :: x
   integer        :: i
   x = 0.0_c_double
   !$omp target teams distribute parallel do reduction(+:x)
   do i = 0, 9
      x = x + 1.0_c_double
   end do
   !$omp end target teams distribute parallel do
end program test

---

Full diff: https://github.com/llvm/llvm-project/pull/145966.diff

1 Files Affected:

• (modified) flang/lib/Lower/OpenMP/OpenMP.cpp (+4)

diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index ebd1d038716e4..b52818e5387a6 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -2395,6 +2395,10 @@ genTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
     if (dsp.getAllSymbolsToPrivatize().contains(&sym))
       return;
 
+    // Skip parameters/constants as they do not need to be mapped.
+    if (semantics::IsNamedConstant(sym))
+      return;
+
     // These symbols are mapped individually in processHasDeviceAddr.
     if (llvm::is_contained(hasDeviceAddrSyms, &sym))
       return;

[skatrak]

Thanks Akash, LGTM!