[clang] [openmp] [Clang][OpenMP] Fix ordering of processing of map clauses when mapping a struct. (PR #72410)

[Johannes Doerfert via cfe-commits]

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@@ -7742,15 +7744,42 @@ class MappableExprsHandler {
       else if (C->getMapType() == OMPC_MAP_alloc)
         Kind = Allocs;
       const auto *EI = C->getVarRefs().begin();
-      for (const auto L : C->component_lists()) {
-        const Expr *E = (C->getMapLoc().isValid()) ? *EI : nullptr;
-        InfoGen(std::get<0>(L), Kind, std::get<1>(L), C->getMapType(),
-                C->getMapTypeModifiers(), std::nullopt,
-                /*ReturnDevicePointer=*/false, C->isImplicit(), std::get<2>(L),
-                E);
-        ++EI;
+      if (*EI && !isa<OMPArraySectionExpr>(*EI)) {
+        for (const auto L : C->component_lists()) {
+          const Expr *E = (C->getMapLoc().isValid()) ? *EI : nullptr;
+          InfoGen(std::get<0>(L), Kind, std::get<1>(L), C->getMapType(),
+                  C->getMapTypeModifiers(), std::nullopt,
+                  /*ReturnDevicePointer=*/false, C->isImplicit(),
+                  std::get<2>(L), E);
+          ++EI;
+        }
+      }
+    }
+
+    // Process the maps with sections.
+    for (const auto *Cl : Clauses) {
+      const auto *C = dyn_cast<OMPMapClause>(Cl);
+      if (!C)
+        continue;
+      MapKind Kind = Other;
+      if (llvm::is_contained(C->getMapTypeModifiers(),
+                             OMPC_MAP_MODIFIER_present))
+        Kind = Present;
+      else if (C->getMapType() == OMPC_MAP_alloc)
+        Kind = Allocs;
+      const auto *EI = C->getVarRefs().begin();
+      if (*EI && isa<OMPArraySectionExpr>(*EI)) {
+        for (const auto L : C->component_lists()) {
+          const Expr *E = (C->getMapLoc().isValid()) ? *EI : nullptr;
+          InfoGen(std::get<0>(L), Kind, std::get<1>(L), C->getMapType(),
+                  C->getMapTypeModifiers(), std::nullopt,
+                  /*ReturnDevicePointer=*/false, C->isImplicit(),
+                  std::get<2>(L), E);
+          ++EI;
+        }
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jdoerfert wrote:

This duplicates the loop nest, which is very unfortunate. Why not actually sort the clause list? That will also make it easier to add/change things in the future, e.g., we simply modify the comparator.

https://github.com/llvm/llvm-project/pull/72410