[Flang][OpenMP] Simplify entry block creation for BlockArgOpenMPOpInterface ops, NFC

This patch adds the `OpWithBodyGenInfo::blockArgs` field and updates
`createBodyOfOp()` to prevent the need for `BlockArgOpenMPOpInterface`
operations to pass the same callback, minimizing chances of introducing
inconsistent behavior.

Author: skatrak

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -1048,6 +1048,11 @@ struct OpWithBodyGenInfo {
     return *this;
   }
 
+  OpWithBodyGenInfo &setEntryBlockArgs(const EntryBlockArgs *value) {
+    blockArgs = value;
+    return *this;
+  }
+
   OpWithBodyGenInfo &setGenRegionEntryCb(GenOMPRegionEntryCBFn value) {
     genRegionEntryCB = value;
     return *this;
@@ -1074,8 +1079,12 @@ struct OpWithBodyGenInfo {
   const List<Clause> *clauses = nullptr;
   /// [in] if provided, processes the construct's data-sharing attributes.
   DataSharingProcessor *dsp = nullptr;
-  /// [in] if provided, emits the op's region entry. Otherwise, an emtpy block
-  /// is created in the region.
+  /// [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.
+  const EntryBlockArgs *blockArgs = nullptr;
+  /// [in] if provided, it overrides the default op's region entry block
+  /// creation.
   GenOMPRegionEntryCBFn genRegionEntryCB = nullptr;
   /// [in] if set to `true`, skip generating nested evaluations and dispatching
   /// any further leaf constructs.
@@ -1099,18 +1108,33 @@ static void createBodyOfOp(mlir::Operation &op, const OpWithBodyGenInfo &info,
     return undef.getDefiningOp();
   };
 
-  // If an argument for the region is provided then create the block with that
-  // argument. Also update the symbol's address with the mlir argument value.
-  // e.g. For loops the argument is the induction variable. And all further
-  // uses of the induction variable should use this mlir value.
+  // Create the entry block for the region and collect its arguments for use
+  // within the region. The entry block will be created as follows:
+  //   - By default, it will be empty and have no arguments.
+  //   - Operations implementing the omp::BlockArgOpenMPOpInterface can set the
+  //     `info.blockArgs` pointer so that block arguments will be those
+  //     corresponding to entry block argument-generating clauses. Binding of
+  //     Fortran symbols to the new MLIR values is done automatically.
+  //   - If the `info.genRegionEntryCB` callback is set, it takes precedence and
+  //     allows callers to manually create the entry block with its intended
+  //     list of arguments and to bind these arguments to their corresponding
+  //     Fortran symbols. This is used for e.g. loop induction variables.
   auto regionArgs = [&]() -> llvm::SmallVector<const semantics::Symbol *> {
-    if (info.genRegionEntryCB != nullptr) {
+    if (info.genRegionEntryCB)
       return info.genRegionEntryCB(&op);
+
+    if (info.blockArgs) {
+      genEntryBlock(firOpBuilder, *info.blockArgs, op.getRegion(0));
+      bindEntryBlockArgs(info.converter,
+                         llvm::cast<mlir::omp::BlockArgOpenMPOpInterface>(op),
+                         *info.blockArgs);
+      return llvm::to_vector(info.blockArgs->getSyms());
     }
 
     firOpBuilder.createBlock(&op.getRegion(0));
     return {};
   }();
+
   // Mark the earliest insertion point.
   mlir::Operation *marker = insertMarker(firOpBuilder);
 
@@ -1978,20 +2002,14 @@ genParallelOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
               mlir::omp::ParallelOperands &clauseOps,
               const EntryBlockArgs &args, DataSharingProcessor *dsp,
               bool isComposite = false) {
-  auto genRegionEntryCB = [&](mlir::Operation *op) {
-    genEntryBlock(converter.getFirOpBuilder(), args, op->getRegion(0));
-    bindEntryBlockArgs(
-        converter, llvm::cast<mlir::omp::BlockArgOpenMPOpInterface>(op), args);
-    return llvm::to_vector(args.getSyms());
-  };
-
   assert((!enableDelayedPrivatization || dsp) &&
          "expected valid DataSharingProcessor");
+
   OpWithBodyGenInfo genInfo =
       OpWithBodyGenInfo(converter, symTable, semaCtx, loc, eval,
                         llvm::omp::Directive::OMPD_parallel)
           .setClauses(&item->clauses)
-          .setGenRegionEntryCb(genRegionEntryCB)
+          .setEntryBlockArgs(&args)
           .setGenSkeletonOnly(isComposite)
           .setDataSharingProcessor(dsp);
 
@@ -2067,13 +2085,6 @@ genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
   mlir::Operation *terminator =
       lower::genOpenMPTerminator(builder, sectionsOp, loc);
 
-  auto genRegionEntryCB = [&](mlir::Operation *op) {
-    genEntryBlock(builder, args, op->getRegion(0));
-    bindEntryBlockArgs(
-        converter, llvm::cast<mlir::omp::BlockArgOpenMPOpInterface>(op), args);
-    return llvm::to_vector(args.getSyms());
-  };
-
   // Generate nested SECTION constructs.
   // This is done here rather than in genOMP([...], OpenMPSectionConstruct )
   // because we need to run genReductionVars on each omp.section so that the
@@ -2097,7 +2108,7 @@ genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
         OpWithBodyGenInfo(converter, symTable, semaCtx, loc, nestedEval,
                           llvm::omp::Directive::OMPD_section)
             .setClauses(&sectionQueue.begin()->clauses)
-            .setGenRegionEntryCb(genRegionEntryCB),
+            .setEntryBlockArgs(&args),
         sectionQueue, sectionQueue.begin());
   }
 
@@ -2436,20 +2447,12 @@ genTaskOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
   taskArgs.priv.syms = dsp.getDelayedPrivSymbols();
   taskArgs.priv.vars = clauseOps.privateVars;
 
-  auto genRegionEntryCB = [&](mlir::Operation *op) {
-    genEntryBlock(converter.getFirOpBuilder(), taskArgs, op->getRegion(0));
-    bindEntryBlockArgs(converter,
-                       llvm::cast<mlir::omp::BlockArgOpenMPOpInterface>(op),
-                       taskArgs);
-    return llvm::to_vector(taskArgs.priv.syms);
-  };
-
   return genOpWithBody<mlir::omp::TaskOp>(
       OpWithBodyGenInfo(converter, symTable, semaCtx, loc, eval,
                         llvm::omp::Directive::OMPD_task)
           .setClauses(&item->clauses)
           .setDataSharingProcessor(&dsp)
-          .setGenRegionEntryCb(genRegionEntryCB),
+          .setEntryBlockArgs(&taskArgs),
       queue, item, clauseOps);
 }
 
@@ -2525,18 +2528,11 @@ genTeamsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
   args.reduction.syms = reductionSyms;
   args.reduction.vars = clauseOps.reductionVars;
 
-  auto genRegionEntryCB = [&](mlir::Operation *op) {
-    genEntryBlock(converter.getFirOpBuilder(), args, op->getRegion(0));
-    bindEntryBlockArgs(
-        converter, llvm::cast<mlir::omp::BlockArgOpenMPOpInterface>(op), args);
-    return llvm::to_vector(args.getSyms());
-  };
-
   return genOpWithBody<mlir::omp::TeamsOp>(
       OpWithBodyGenInfo(converter, symTable, semaCtx, loc, eval,
                         llvm::omp::Directive::OMPD_teams)
           .setClauses(&item->clauses)
-          .setGenRegionEntryCb(genRegionEntryCB),
+          .setEntryBlockArgs(&args),
       queue, item, clauseOps);
 }