[NFC][flang][OpenMP] Unify genSectionsOp's prototype to match other genXXXOp functions (#144013)

Unifies the prototype of `genSectionsOp` to match other ops generators.
Doing so, we are able to call `genSectionsOp` directtly from
`genOMPDispatch` instead of the special handling needed now to pass the
section blocks. This is useful because now we can handle symbol mapping
scopes easier for nested OpenMP directives. See

#143706 (comment)
and the following discussion for more info.

Author: ergawy

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -201,6 +201,8 @@ class HostEvalInfo {
 /// structures, but it will probably still require some further work to support
 /// reverse offloading.
 static llvm::SmallVector<HostEvalInfo, 0> hostEvalInfo;
+static llvm::SmallVector<const parser::OpenMPSectionsConstruct *, 0>
+    sectionsStack;
 
 /// Bind symbols to their corresponding entry block arguments.
 ///
@@ -2220,8 +2222,12 @@ static mlir::omp::SectionsOp
 genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
               semantics::SemanticsContext &semaCtx,
               lower::pft::Evaluation &eval, mlir::Location loc,
-              const ConstructQueue &queue, ConstructQueue::const_iterator item,
-              const parser::OmpSectionBlocks &sectionBlocks) {
+              const ConstructQueue &queue,
+              ConstructQueue::const_iterator item) {
+  assert(!sectionsStack.empty());
+  const auto &sectionBlocks =
+      std::get<parser::OmpSectionBlocks>(sectionsStack.back()->t);
+  sectionsStack.pop_back();
   mlir::omp::SectionsOperands clauseOps;
   llvm::SmallVector<const semantics::Symbol *> reductionSyms;
   genSectionsClauses(converter, semaCtx, item->clauses, loc, clauseOps,
@@ -3458,10 +3464,7 @@ static void genOMPDispatch(lower::AbstractConverter &converter,
     // Lowered in the enclosing genSectionsOp.
     break;
   case llvm::omp::Directive::OMPD_sections:
-    // Called directly from genOMP([...], OpenMPSectionsConstruct) because it
-    // has a different prototype.
-    // This code path is still taken when iterating through the construct queue
-    // in genBodyOfOp
+    genSectionsOp(converter, symTable, semaCtx, eval, loc, queue, item);
     break;
   case llvm::omp::Directive::OMPD_simd:
     newOp =
@@ -4137,8 +4140,6 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
       std::get<parser::OmpClauseList>(beginSectionsDirective.t), semaCtx);
   const auto &endSectionsDirective =
       std::get<parser::OmpEndSectionsDirective>(sectionsConstruct.t);
-  const auto &sectionBlocks =
-      std::get<parser::OmpSectionBlocks>(sectionsConstruct.t);
   clauses.append(makeClauses(
       std::get<parser::OmpClauseList>(endSectionsDirective.t), semaCtx));
   mlir::Location currentLocation = converter.getCurrentLocation();
@@ -4150,22 +4151,10 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
   ConstructQueue queue{
       buildConstructQueue(converter.getFirOpBuilder().getModule(), semaCtx,
                           eval, source, directive, clauses)};
-  ConstructQueue::iterator next = queue.begin();
-  // Generate constructs that come first e.g. Parallel
-  while (next != queue.end() &&
-         next->id != llvm::omp::Directive::OMPD_sections) {
-    genOMPDispatch(converter, symTable, semaCtx, eval, currentLocation, queue,
-                   next);
-    next = std::next(next);
-  }
 
-  // call genSectionsOp directly (not via genOMPDispatch) so that we can add the
-  // sectionBlocks argument
-  assert(next != queue.end());
-  assert(next->id == llvm::omp::Directive::OMPD_sections);
-  genSectionsOp(converter, symTable, semaCtx, eval, currentLocation, queue,
-                next, sectionBlocks);
-  assert(std::next(next) == queue.end());
+  sectionsStack.push_back(&sectionsConstruct);
+  genOMPDispatch(converter, symTable, semaCtx, eval, currentLocation, queue,
+                 queue.begin());
 }
 
 static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,