[flang-commits] [flang] 044e1aa - [flang][OpenMP] move omp end sections validation to semantics (#154740)

[via flang-commits]

Author: Tom Eccles
Date: 2025-08-26T10:45:56Z
New Revision: 044e1aabbd4b92a2e05a52e9a1630c2fe548d358

URL: https://github.com/llvm/llvm-project/commit/044e1aabbd4b92a2e05a52e9a1630c2fe548d358
DIFF: https://github.com/llvm/llvm-project/commit/044e1aabbd4b92a2e05a52e9a1630c2fe548d358.diff

LOG: [flang][OpenMP] move omp end sections validation to semantics (#154740)

See #90452. The old parse tree errors exploded to thousands of unhelpful
lines when there were multiple missing end directives.

Instead, allow a missing end directive in the parse tree then validate
that it is present during semantics (where the error messages are a lot
easier to control).

Added: 
    

Modified: 
    flang/include/flang/Parser/parse-tree.h
    flang/lib/Lower/OpenMP/OpenMP.cpp
    flang/lib/Parser/openmp-parsers.cpp
    flang/lib/Parser/unparse.cpp
    flang/lib/Semantics/check-omp-structure.cpp
    flang/test/Semantics/OpenMP/missing-end-directive.f90

Removed: 
    


################################################################################
diff  --git a/flang/include/flang/Parser/parse-tree.h b/flang/include/flang/Parser/parse-tree.h
index 1d1a4a163084b..6604e42957f84 100644
--- a/flang/include/flang/Parser/parse-tree.h
+++ b/flang/include/flang/Parser/parse-tree.h
@@ -4893,8 +4893,11 @@ struct OpenMPSectionsConstruct {
   CharBlock source;
   // Each of the OpenMPConstructs in the list below contains an
   // OpenMPSectionConstruct. This is guaranteed by the parser.
+  // The end sections directive is optional here because it is 
diff icult to
+  // generate helpful error messages for a missing end directive within the
+  // parser. Semantics will generate an error if this is absent.
   std::tuple<OmpBeginSectionsDirective, std::list<OpenMPConstruct>,
-      OmpEndSectionsDirective>
+      std::optional<OmpEndSectionsDirective>>
       t;
 };
 

diff  --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 1044b7ad31202..c3ee67f4b3461 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -3979,9 +3979,12 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
   List<Clause> clauses = makeClauses(
       std::get<parser::OmpClauseList>(beginSectionsDirective.t), semaCtx);
   const auto &endSectionsDirective =
-      std::get<parser::OmpEndSectionsDirective>(sectionsConstruct.t);
+      std::get<std::optional<parser::OmpEndSectionsDirective>>(
+          sectionsConstruct.t);
+  assert(endSectionsDirective &&
+         "Missing end section directive should have been handled in semantics");
   clauses.append(makeClauses(
-      std::get<parser::OmpClauseList>(endSectionsDirective.t), semaCtx));
+      std::get<parser::OmpClauseList>(endSectionsDirective->t), semaCtx));
   mlir::Location currentLocation = converter.getCurrentLocation();
 
   llvm::omp::Directive directive =

diff  --git a/flang/lib/Parser/openmp-parsers.cpp b/flang/lib/Parser/openmp-parsers.cpp
index c5a80e0c87092..5c17ddff8d7d3 100644
--- a/flang/lib/Parser/openmp-parsers.cpp
+++ b/flang/lib/Parser/openmp-parsers.cpp
@@ -1921,7 +1921,7 @@ TYPE_PARSER(sourced(construct<OpenMPSectionsConstruct>(
             construct<OpenMPSectionConstruct>(maybe(sectionDir), block))),
         many(construct<OpenMPConstruct>(
             sourced(construct<OpenMPSectionConstruct>(sectionDir, block))))),
-    Parser<OmpEndSectionsDirective>{} / endOmpLine)))
+    maybe(Parser<OmpEndSectionsDirective>{} / endOmpLine))))
 
 static bool IsExecutionPart(const OmpDirectiveName &name) {
   return name.IsExecutionPart();

diff  --git a/flang/lib/Parser/unparse.cpp b/flang/lib/Parser/unparse.cpp
index 09dcfe60a46bc..87e699dbc4e8d 100644
--- a/flang/lib/Parser/unparse.cpp
+++ b/flang/lib/Parser/unparse.cpp
@@ -2788,7 +2788,7 @@ class UnparseVisitor {
     Walk(std::get<std::list<OpenMPConstruct>>(x.t), "");
     BeginOpenMP();
     Word("!$OMP END ");
-    Walk(std::get<OmpEndSectionsDirective>(x.t));
+    Walk(std::get<std::optional<OmpEndSectionsDirective>>(x.t));
     Put("\n");
     EndOpenMP();
   }

diff  --git a/flang/lib/Semantics/check-omp-structure.cpp b/flang/lib/Semantics/check-omp-structure.cpp
index 3a7d1ed3ce7f9..04f2ebcbcaee2 100644
--- a/flang/lib/Semantics/check-omp-structure.cpp
+++ b/flang/lib/Semantics/check-omp-structure.cpp
@@ -1138,14 +1138,23 @@ void OmpStructureChecker::Leave(const parser::OmpBeginDirective &) {
 void OmpStructureChecker::Enter(const parser::OpenMPSectionsConstruct &x) {
   const auto &beginSectionsDir{
       std::get<parser::OmpBeginSectionsDirective>(x.t)};
-  const auto &endSectionsDir{std::get<parser::OmpEndSectionsDirective>(x.t)};
+  const auto &endSectionsDir{
+      std::get<std::optional<parser::OmpEndSectionsDirective>>(x.t)};
   const auto &beginDir{
       std::get<parser::OmpSectionsDirective>(beginSectionsDir.t)};
-  const auto &endDir{std::get<parser::OmpSectionsDirective>(endSectionsDir.t)};
+  PushContextAndClauseSets(beginDir.source, beginDir.v);
+
+  if (!endSectionsDir) {
+    context_.Say(beginSectionsDir.source,
+        "Expected OpenMP END SECTIONS directive"_err_en_US);
+    // Following code assumes the option is present.
+    return;
+  }
+
+  const auto &endDir{std::get<parser::OmpSectionsDirective>(endSectionsDir->t)};
   CheckMatching<parser::OmpSectionsDirective>(beginDir, endDir);
 
-  PushContextAndClauseSets(beginDir.source, beginDir.v);
-  AddEndDirectiveClauses(std::get<parser::OmpClauseList>(endSectionsDir.t));
+  AddEndDirectiveClauses(std::get<parser::OmpClauseList>(endSectionsDir->t));
 
   const auto &sectionBlocks{std::get<std::list<parser::OpenMPConstruct>>(x.t)};
   for (const parser::OpenMPConstruct &construct : sectionBlocks) {

diff  --git a/flang/test/Semantics/OpenMP/missing-end-directive.f90 b/flang/test/Semantics/OpenMP/missing-end-directive.f90
index 3b870d134155b..33481f9d650f4 100644
--- a/flang/test/Semantics/OpenMP/missing-end-directive.f90
+++ b/flang/test/Semantics/OpenMP/missing-end-directive.f90
@@ -6,8 +6,12 @@
 !$omp parallel
 ! ERROR: Expected OpenMP end directive
 !$omp task
+! ERROR: Expected OpenMP END SECTIONS directive
+!$omp sections
 ! ERROR: Expected OpenMP end directive
 !$omp parallel
 ! ERROR: Expected OpenMP end directive
 !$omp task
+! ERROR: Expected OpenMP END SECTIONS directive
+!$omp sections
 end