[flang][OpenMP] fix predetermined privatization inside section

This now produces code equivalent to if there was an explicit private
clause on the SECTIONS construct.

The problem was that each SECTION construct got its own DSP, which tried
to privatize the same symbol for that SECTION. Privatization for
SECTION(S) happens on the outer SECTION construct and so the outer
construct's DSP should be shared.

Fixes #135108

Author: tblah

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -1057,6 +1057,11 @@ struct OpWithBodyGenInfo {
     return *this;
   }
 
+  OpWithBodyGenInfo &setSkipDspStep2(bool value) {
+    skipDspStep2 = value;
+    return *this;
+  }
+
   OpWithBodyGenInfo &setEntryBlockArgs(const EntryBlockArgs *value) {
     blockArgs = value;
     return *this;
@@ -1088,6 +1093,8 @@ struct OpWithBodyGenInfo {
   const List<Clause> *clauses = nullptr;
   /// [in] if provided, processes the construct's data-sharing attributes.
   DataSharingProcessor *dsp = nullptr;
+  /// [in] if true, skip DataSharingProcessor::processStep2
+  bool skipDspStep2 = false;
   /// [in] if provided, it is used to create the op's region entry block. It is
   /// overriden when a \see genRegionEntryCB is provided. This is only valid for
   /// operations implementing the \see mlir::omp::BlockArgOpenMPOpInterface.
@@ -1240,7 +1247,7 @@ static void createBodyOfOp(mlir::Operation &op, const OpWithBodyGenInfo &info,
     // loop (this may not make sense in production code, but a user could
     // write that and we should handle it).
     firOpBuilder.setInsertionPoint(term);
-    if (privatize) {
+    if (privatize && !info.skipDspStep2) {
       // DataSharingProcessor::processStep2() may create operations before/after
       // the one passed as argument. We need to treat loop wrappers and their
       // nested loop as a unit, so we need to pass the bottom level wrapper (if
@@ -2162,7 +2169,10 @@ genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
         OpWithBodyGenInfo(converter, symTable, semaCtx, loc, nestedEval,
                           llvm::omp::Directive::OMPD_section)
             .setClauses(&sectionQueue.begin()->clauses)
-            .setEntryBlockArgs(&args),
+            .setEntryBlockArgs(&args)
+            .setDataSharingProcessor(&dsp)
+            // lastprivate is handled differently for SECTIONS, see below
+            .setSkipDspStep2(true),
         sectionQueue, sectionQueue.begin());
   }
 

flang/test/Lower/OpenMP/sections-predetermined-private.f90

@@ -0,0 +1,34 @@
+! RUN: %flang_fc1 -fopenmp -emit-hlfir -o - %s | FileCheck %s
+
+!$omp parallel sections
+!$omp section
+    do i = 1, 2
+    end do
+!$omp section
+    do i = 1, 2
+    end do
+!$omp end parallel sections
+end
+! CHECK-LABEL:   func.func @_QQmain() {
+! CHECK:           omp.parallel {
+! CHECK:             %[[VAL_3:.*]] = fir.alloca i32 {bindc_name = "i", pinned}
+! CHECK:             %[[VAL_4:.*]]:2 = hlfir.declare %[[VAL_3]] {uniq_name = "_QFEi"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+! CHECK:             omp.sections {
+! CHECK:               omp.section {
+! CHECK:                 %[[VAL_11:.*]]:2 = fir.do_loop %[[VAL_12:.*]] = %{{.*}} to %{{.*}} step %{{.*}} iter_args(%{{.*}} = %{{.*}} -> (index, i32) {
+! CHECK:                 }
+! CHECK:                 fir.store %[[VAL_11]]#1 to %[[VAL_4]]#0 : !fir.ref<i32>
+! CHECK:                 omp.terminator
+! CHECK:               }
+! CHECK:               omp.section {
+! CHECK:                 %[[VAL_25:.*]]:2 = fir.do_loop %[[VAL_26:.*]] = %{{.*}} to %{{.*}} step %{{.*}} iter_args(%{{.*}} = %{{.*}}) -> (index, i32) {
+! CHECK:                 }
+! CHECK:                 fir.store %[[VAL_25]]#1 to %[[VAL_4]]#0 : !fir.ref<i32>
+! CHECK:                 omp.terminator
+! CHECK:               }
+! CHECK:               omp.terminator
+! CHECK:             }
+! CHECK:             omp.terminator
+! CHECK:           }
+! CHECK:           return
+! CHECK:         }