[flang][openmp]Add UserReductionDetails and use in DECLARE REDUCTION (#140066)

This adds another puzzle piece for the support of OpenMP DECLARE
REDUCTION functionality.

This adds support for operators with derived types, as well as declaring
multiple different types with the same name or operator.

A new detail class for UserReductionDetials is introduced to hold the
list of types supported for a given reduction declaration.

Tests for parsing and symbol generation added.

Declare reduction is still not supported to lowering, it will generate a
"Not yet implemented" fatal error.

Fixes #141306
Fixes #97241
Fixes #92832
Fixes #66453

---------

Co-authored-by: Mats Petersson <mats.petersson@arm.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index a1ec956..a726418 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -894,6 +894,7 @@ void ModFileWriter::PutEntity(llvm::raw_ostream &os, const Symbol &symbol) {
           [&](const ObjectEntityDetails &) { PutObjectEntity(os, symbol); },
           [&](const ProcEntityDetails &) { PutProcEntity(os, symbol); },
           [&](const TypeParamDetails &) { PutTypeParam(os, symbol); },
+          [&](const UserReductionDetails &) { PutUserReduction(os, symbol); },
           [&](const auto &) {
             common::die("PutEntity: unexpected details: %s",
                 DetailsToString(symbol.details()).c_str());
@@ -1043,6 +1044,28 @@ void ModFileWriter::PutTypeParam(llvm::raw_ostream &os, const Symbol &symbol) {
   os << '\n';
 }
 
+void ModFileWriter::PutUserReduction(
+    llvm::raw_ostream &os, const Symbol &symbol) {
+  const auto &details{symbol.get<UserReductionDetails>()};
+  // The module content for a OpenMP Declare Reduction is the OpenMP
+  // declaration. There may be multiple declarations.
+  // Decls are pointers, so do not use a reference.
+  for (const auto decl : details.GetDeclList()) {
+    common::visit( //
+        common::visitors{//
+            [&](const parser::OpenMPDeclareReductionConstruct *d) {
+              Unparse(os, *d, context_.langOptions());
+            },
+            [&](const parser::OmpMetadirectiveDirective *m) {
+              Unparse(os, *m, context_.langOptions());
+            },
+            [&](const auto &) {
+              DIE("Unknown OpenMP DECLARE REDUCTION content");
+            }},
+        decl);
+  }
+}
+
 void PutInit(llvm::raw_ostream &os, const Symbol &symbol, const MaybeExpr &init,
     const parser::Expr *unanalyzed, SemanticsContext &context) {
   if (IsNamedConstant(symbol) || symbol.owner().IsDerivedType()) {