commit daa18205c6f0a3b5dd62ba2e65948e1a9182a60f
author Kaviya Rajendiran <67495422+kaviya2510@users.noreply.github.com> Thu Jan 23 11:14:00 2025 +0530
committer GitHub <noreply@github.com> Thu Jan 23 11:14:00 2025 +0530
tree 6e486c0bac19f1b237dc917afa367d0be78a835b
parent 646f034e4e228f9d5d6a0142210e5e28f2ea7872

[Flang][OpenMP] Fix copyin allocatable lowering to MLIR (#122097)

Fixes https://github.com/llvm/llvm-project/issues/113191

Issue: [flang][OpenMP] Runtime segfault when an allocatable variable is
used with copyin

Rootcause: The value of the threadprivate variable is not being copied
from the primary thread to the other threads within a parallel region.
As a result it tries to access a null pointer inside a parallel region
which causes segfault.

Fix: When allocatables used with copyin clause need to ensure that, on
entry to any parallel region each thread’s copy of a variable will
acquire the allocation status of the primary thread, before copying the
value of a threadprivate variable of the primary thread to the
threadprivate variable of each other member of the team.

flang/lib/Lower/Bridge.cpp

diff --git a/flang/lib/Lower/Bridge.cpp b/flang/lib/Lower/Bridge.cpp
index 700ca56..d92dc0c 100644
--- a/flang/lib/Lower/Bridge.cpp
+++ b/flang/lib/Lower/Bridge.cpp
@@ -1290,9 +1290,30 @@
       auto loadVal = builder->create<fir::LoadOp>(loc, rhs);
       builder->create<fir::StoreOp>(loc, loadVal, lhs);
     } else if (isAllocatable &&
-               (flags.test(Fortran::semantics::Symbol::Flag::OmpFirstPrivate) ||
-                flags.test(Fortran::semantics::Symbol::Flag::OmpCopyIn))) {
-      // For firstprivate and copyin allocatable variables, RHS must be copied
+               flags.test(Fortran::semantics::Symbol::Flag::OmpCopyIn)) {
+      // For copyin allocatable variables, RHS must be copied to lhs
+      // only when rhs is allocated.
+      hlfir::Entity temp =
+          hlfir::derefPointersAndAllocatables(loc, *builder, rhs);
+      mlir::Value addr = hlfir::genVariableRawAddress(loc, *builder, temp);
+      mlir::Value isAllocated = builder->genIsNotNullAddr(loc, addr);
+      builder->genIfThenElse(loc, isAllocated)
+          .genThen([&]() { copyData(lhs, rhs); })
+          .genElse([&]() {
+            fir::ExtendedValue hexv = symBoxToExtendedValue(dst);
+            hexv.match(
+                [&](const fir::MutableBoxValue &new_box) -> void {
+                  // if the allocation status of original list item is
+                  // unallocated, unallocate the copy if it is allocated, else
+                  // do nothing.
+                  Fortran::lower::genDeallocateIfAllocated(*this, new_box, loc);
+                },
+                [&](const auto &) -> void {});
+          })
+          .end();
+    } else if (isAllocatable &&
+               flags.test(Fortran::semantics::Symbol::Flag::OmpFirstPrivate)) {
+      // For firstprivate allocatable variables, RHS must be copied
       // only when LHS is allocated.
       hlfir::Entity temp =
           hlfir::derefPointersAndAllocatables(loc, *builder, lhs);