[Flang][OpenMP] Increase detection capability for requires usm (and others)

Currently, the compiler only picks up some cases where requires is designated
such as in the main program. However, it'll gloss over cases such as when it
is specified by a user in a module, that's then used elsewhere.

This patch attempts to amend that by searching the varying scopes in the
current program module more comprehensively.

Author: agozillon

flang/lib/Lower/Bridge.cpp

@@ -415,7 +415,8 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     // - Define module variables and OpenMP/OpenACC declarative constructs so
     //   they are available before lowering any function that may use them.
     bool hasMainProgram = false;
-    const Fortran::semantics::Symbol *globalOmpRequiresSymbol = nullptr;
+    llvm::SmallVector<const Fortran::semantics::Symbol *>
+        globalOmpRequiresSymbols;
     createBuilderOutsideOfFuncOpAndDo([&]() {
       for (Fortran::lower::pft::Program::Units &u : pft.getUnits()) {
         Fortran::common::visit(
@@ -424,21 +425,23 @@ class FirConverter : public Fortran::lower::AbstractConverter {
                   if (f.isMainProgram())
                     hasMainProgram = true;
                   declareFunction(f);
-                  if (!globalOmpRequiresSymbol)
-                    globalOmpRequiresSymbol = f.getScope().symbol();
+                  globalOmpRequiresSymbols.push_back(f.getScope().symbol());
                 },
                 [&](Fortran::lower::pft::ModuleLikeUnit &m) {
                   lowerModuleDeclScope(m);
                   for (Fortran::lower::pft::ContainedUnit &unit :
                        m.containedUnitList)
                     if (auto *f =
                             std::get_if<Fortran::lower::pft::FunctionLikeUnit>(
-                                &unit))
+                                &unit)) {
                       declareFunction(*f);
+                      globalOmpRequiresSymbols.push_back(
+                          f->getScope().symbol());
+                    }
+                  globalOmpRequiresSymbols.push_back(m.getScope().symbol());
                 },
                 [&](Fortran::lower::pft::BlockDataUnit &b) {
-                  if (!globalOmpRequiresSymbol)
-                    globalOmpRequiresSymbol = b.symTab.symbol();
+                  globalOmpRequiresSymbols.push_back(b.symTab.symbol());
                 },
                 [&](Fortran::lower::pft::CompilerDirectiveUnit &d) {},
                 [&](Fortran::lower::pft::OpenACCDirectiveUnit &d) {},
@@ -481,7 +484,7 @@ class FirConverter : public Fortran::lower::AbstractConverter {
                                   Fortran::common::LanguageFeature::Coarray));
       });
 
-    finalizeOpenMPLowering(globalOmpRequiresSymbol);
+    finalizeOpenMPLowering(globalOmpRequiresSymbols);
   }
 
   /// Declare a function.
@@ -6681,7 +6684,8 @@ class FirConverter : public Fortran::lower::AbstractConverter {
   /// Performing OpenMP lowering actions that were deferred to the end of
   /// lowering.
   void finalizeOpenMPLowering(
-      const Fortran::semantics::Symbol *globalOmpRequiresSymbol) {
+      llvm::SmallVectorImpl<const Fortran::semantics::Symbol *>
+          &globalOmpRequiresSymbol) {
     if (!ompDeferredDeclareTarget.empty()) {
       bool deferredDeviceFuncFound =
           Fortran::lower::markOpenMPDeferredDeclareTargetFunctions(
@@ -6690,9 +6694,10 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     }
 
     // Set the module attribute related to OpenMP requires directives
-    if (ompDeviceCodeFound)
-      Fortran::lower::genOpenMPRequires(getModuleOp().getOperation(),
-                                        globalOmpRequiresSymbol);
+    if (ompDeviceCodeFound) {
+      for (auto sym : globalOmpRequiresSymbol)
+        Fortran::lower::genOpenMPRequires(getModuleOp().getOperation(), sym);
+    }
   }
 
   /// Record fir.dummy_scope operation for this function.

flang/test/Lower/OpenMP/requires-usm.f90

@@ -0,0 +1,22 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+! RUN: %flang_fc1 -emit-hlfir -fopenmp -fopenmp-is-target-device %s -o - | FileCheck %s
+! RUN: bbc -fopenmp -emit-hlfir %s -o - | FileCheck %s
+! RUN: bbc -fopenmp -fopenmp-is-target-device -emit-hlfir %s -o - | FileCheck %s
+
+! Verify that we pick up USM and apply it correctly when it is specified
+! outside of the program.
+
+!CHECK:      module attributes {
+!CHECK-SAME: omp.requires = #omp<clause_requires unified_shared_memory>
+module declare_mod
+    implicit none
+!$omp requires unified_shared_memory
+ contains
+end module
+
+program main
+ use declare_mod
+ implicit none
+!$omp target
+!$omp end target
+end program