[flang-commits] [flang] [Flang][OpenMP] Fix crash and IR errors for user-defined reduction on allocatable variables (PR #186765)

[via flang-commits]

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@@ -803,6 +804,185 @@ bool ReductionProcessor::processReductionArguments(
                          &redOperator.u)) {
         if (!ReductionProcessor::supportedIntrinsicProcReduction(
                 *reductionIntrinsic)) {
+          if (isByRef) {
+            // create a new declare_reduction for the boxed type, reusing
+            // the existing init and combiner
+            semantics::Symbol *sym = reductionIntrinsic->v.sym();
+            llvm::StringRef baseName = {sym->name().begin(),
+                                        sym->name().size()};
+            mlir::ModuleOp module = builder.getModule();
+            auto existingDecl = module.lookupSymbol<OpType>(baseName);
+            if (!existingDecl) {
+              TODO(currentLocation,
+                   "User-defined reductions on allocatable or pointer "
+                   "variables: cannot find base reduction declaration");
+            }
+
+            std::string byrefName = getReductionName(
+                baseName, builder.getKindMap(), redType, isByRef);
+
+            mlir::Region &existingInitRegion =
+                existingDecl.getInitializerRegion();
+            auto genInitValueCB =
+                [&existingInitRegion](fir::FirOpBuilder &builder,
+                                      mlir::Location loc, mlir::Type elemTy,
+                                      mlir::Value) -> mlir::Value {
+              // unwrap box type to get the scalar element type
+              mlir::Type scalarTy = unwrapSeqOrBoxedType(elemTy);
+              // find a constant-producing op in the existing init region
+              mlir::Operation *constOp = nullptr;
+              existingInitRegion.walk([&](mlir::Operation *op) {
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MattPD wrote:

Verified: the scalar `omp_priv = omp_orig` path reads the original element, and the array case is a clean TODO. Thanks.

https://github.com/llvm/llvm-project/pull/186765