[flang][OpenMP] fix predetermined privatization inside section (#138159)

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/DataSharingProcessor.cpp

@@ -67,6 +67,8 @@ void DataSharingProcessor::processStep1(
 
 void DataSharingProcessor::processStep2(mlir::Operation *op, bool isLoop) {
   // 'sections' lastprivate is handled by genOMP()
+  if (mlir::isa<mlir::omp::SectionOp>(op))
+    return;
   if (!mlir::isa<mlir::omp::SectionsOp>(op)) {
     mlir::OpBuilder::InsertionGuard guard(firOpBuilder);
     copyLastPrivatize(op);

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -2154,6 +2154,7 @@ genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
         OpWithBodyGenInfo(converter, symTable, semaCtx, loc, nestedEval,
                           llvm::omp::Directive::OMPD_section)
             .setClauses(&sectionQueue.begin()->clauses)
+            .setDataSharingProcessor(&dsp)
             .setEntryBlockArgs(&args),
         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:         }