[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);
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MattPD wrote:

Our reduction stack #207491-#207494 touches this same file. It gives reduction ops their symbol name via a helper, `getScopedUserReductionName` (scope-qualified base + per-type and by-ref suffix), used on both the directive materializer and the clause side so they bind.

The boxed op you create here takes the bare `sym->name()`, so once the trees combine it won't match the clause-side lookup, and boxed allocatable/pointer reductions won't lower. Whoever rebases second, could the boxed op here be named from `getScopedUserReductionName` (with the operand's type and `isByRef`) instead? Both `lookupSymbol<OpType>(baseName)` and `byrefName` would use it.

#207494 leaves exactly this case (boxed trivial-type allocatable/pointer) as a clean TODO gated by `isBoxedTrivialReduction`, precisely so #186765 can own it. The same rebase also shifts `declare-reduction-allocatable.f90` CHECK names to the scoped form. Happy to handle that naming on our side, or coordinate however's easiest.

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