[Flang][MLIR] Add !$omp unroll construct and omp.unroll_heuristic modeling

Author: Meinersbur

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -2128,6 +2128,161 @@ genLoopOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
   return loopOp;
 }
 
+static mlir::omp::CanonicalLoopOp
+genCanonicalLoopOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
+                   semantics::SemanticsContext &semaCtx,
+                   lower::pft::Evaluation &eval, mlir::Location loc,
+                   const ConstructQueue &queue,
+                   ConstructQueue::const_iterator item,
+                   llvm::ArrayRef<const semantics::Symbol *> ivs,
+                   llvm::omp::Directive directive, DataSharingProcessor &dsp) {
+  fir::FirOpBuilder &firOpBuilder = converter.getFirOpBuilder();
+
+  assert(ivs.size() == 1 && "Nested loops not yet implemented");
+  const semantics::Symbol *iv = ivs[0];
+
+  auto &nestedEval = eval.getFirstNestedEvaluation();
+  if (nestedEval.getIf<parser::DoConstruct>()->IsDoConcurrent()) {
+    TODO(loc, "Do Concurrent in unroll construct");
+  }
+
+  // Get the loop bounds (and increment)
+  auto &doLoopEval = nestedEval.getFirstNestedEvaluation();
+  auto *doStmt = doLoopEval.getIf<parser::NonLabelDoStmt>();
+  assert(doStmt && "Expected do loop to be in the nested evaluation");
+  auto &loopControl = std::get<std::optional<parser::LoopControl>>(doStmt->t);
+  assert(loopControl.has_value());
+  auto *bounds = std::get_if<parser::LoopControl::Bounds>(&loopControl->u);
+  assert(bounds && "Expected bounds for canonical loop");
+  lower::StatementContext stmtCtx;
+  mlir::Value loopLBVar = fir::getBase(
+      converter.genExprValue(*semantics::GetExpr(bounds->lower), stmtCtx));
+  mlir::Value loopUBVar = fir::getBase(
+      converter.genExprValue(*semantics::GetExpr(bounds->upper), stmtCtx));
+  mlir::Value loopStepVar = [&]() {
+    if (bounds->step) {
+      return fir::getBase(
+          converter.genExprValue(*semantics::GetExpr(bounds->step), stmtCtx));
+    } else {
+      // If `step` is not present, assume it is `1`.
+      return firOpBuilder.createIntegerConstant(loc, firOpBuilder.getI32Type(),
+                                                1);
+    }
+  }();
+
+  // Get the integer kind for the loop variable and cast the loop bounds
+  size_t loopVarTypeSize = bounds->name.thing.symbol->GetUltimate().size();
+  mlir::Type loopVarType = getLoopVarType(converter, loopVarTypeSize);
+  loopLBVar = firOpBuilder.createConvert(loc, loopVarType, loopLBVar);
+  loopUBVar = firOpBuilder.createConvert(loc, loopVarType, loopUBVar);
+  loopStepVar = firOpBuilder.createConvert(loc, loopVarType, loopStepVar);
+
+  // Start lowering
+  mlir::Value zero = firOpBuilder.createIntegerConstant(loc, loopVarType, 0);
+  mlir::Value one = firOpBuilder.createIntegerConstant(loc, loopVarType, 1);
+  mlir::Value isDownwards = firOpBuilder.create<mlir::arith::CmpIOp>(
+      loc, mlir::arith::CmpIPredicate::slt, loopStepVar, zero);
+
+  // Ensure we are counting upwards. If not, negate step and swap lb and ub.
+  mlir::Value negStep =
+      firOpBuilder.create<mlir::arith::SubIOp>(loc, zero, loopStepVar);
+  mlir::Value incr = firOpBuilder.create<mlir::arith::SelectOp>(
+      loc, isDownwards, negStep, loopStepVar);
+  mlir::Value lb = firOpBuilder.create<mlir::arith::SelectOp>(
+      loc, isDownwards, loopUBVar, loopLBVar);
+  mlir::Value ub = firOpBuilder.create<mlir::arith::SelectOp>(
+      loc, isDownwards, loopLBVar, loopUBVar);
+
+  // Compute the trip count assuming lb <= ub. This guarantees that the result
+  // is non-negative and we can use unsigned arithmetic.
+  mlir::Value span = firOpBuilder.create<mlir::arith::SubIOp>(
+      loc, ub, lb, ::mlir::arith::IntegerOverflowFlags::nuw);
+  mlir::Value tcMinusOne =
+      firOpBuilder.create<mlir::arith::DivUIOp>(loc, span, incr);
+  mlir::Value tcIfLooping = firOpBuilder.create<mlir::arith::AddIOp>(
+      loc, tcMinusOne, one, ::mlir::arith::IntegerOverflowFlags::nuw);
+
+  // Fall back to 0 if lb > ub
+  mlir::Value isZeroTC = firOpBuilder.create<mlir::arith::CmpIOp>(
+      loc, mlir::arith::CmpIPredicate::slt, ub, lb);
+  mlir::Value tripcount = firOpBuilder.create<mlir::arith::SelectOp>(
+      loc, isZeroTC, zero, tcIfLooping);
+
+  // Create the CLI handle.
+  auto newcli = firOpBuilder.create<mlir::omp::NewCliOp>(loc);
+  mlir::Value cli = newcli.getResult();
+
+  auto ivCallback = [&](mlir::Operation *op)
+      -> llvm::SmallVector<const Fortran::semantics::Symbol *> {
+    mlir::Region &region = op->getRegion(0);
+
+    // Create the op's region skeleton (BB taking the iv as argument)
+    firOpBuilder.createBlock(&region, {}, {loopVarType}, {loc});
+
+    // Compute the value of the loop variable from the logical iteration number.
+    mlir::Value natIterNum = fir::getBase(region.front().getArgument(0));
+    mlir::Value scaled =
+        firOpBuilder.create<mlir::arith::MulIOp>(loc, natIterNum, loopStepVar);
+    mlir::Value userVal =
+        firOpBuilder.create<mlir::arith::AddIOp>(loc, loopLBVar, scaled);
+
+    // The argument is not currently in memory, so make a temporary for the
+    // argument, and store it there, then bind that location to the argument.
+    mlir::Operation *storeOp =
+        createAndSetPrivatizedLoopVar(converter, loc, userVal, iv);
+
+    firOpBuilder.setInsertionPointAfter(storeOp);
+    return {iv};
+  };
+
+  // Create the omp.canonical_loop operation
+  auto canonLoop = genOpWithBody<mlir::omp::CanonicalLoopOp>(
+      OpWithBodyGenInfo(converter, symTable, semaCtx, loc, nestedEval,
+                        directive)
+          .setClauses(&item->clauses)
+          .setDataSharingProcessor(&dsp)
+          .setGenRegionEntryCb(ivCallback),
+      queue, item, tripcount, cli);
+
+  firOpBuilder.setInsertionPointAfter(canonLoop);
+  return canonLoop;
+}
+
+static void genUnrollOp(Fortran::lower::AbstractConverter &converter,
+                        Fortran::lower::SymMap &symTable,
+                        lower::StatementContext &stmtCtx,
+                        Fortran::semantics::SemanticsContext &semaCtx,
+                        Fortran::lower::pft::Evaluation &eval,
+                        mlir::Location loc, const ConstructQueue &queue,
+                        ConstructQueue::const_iterator item) {
+  fir::FirOpBuilder &firOpBuilder = converter.getFirOpBuilder();
+
+  mlir::omp::LoopRelatedClauseOps loopInfo;
+  llvm::SmallVector<const semantics::Symbol *> iv;
+  collectLoopRelatedInfo(converter, loc, eval, item->clauses, loopInfo, iv);
+
+  // Clauses for unrolling not yet implemnted
+  ClauseProcessor cp(converter, semaCtx, item->clauses);
+  cp.processTODO<clause::Partial, clause::Full>(
+      loc, llvm::omp::Directive::OMPD_unroll);
+
+  // Even though unroll does not support data-sharing clauses, but this is
+  // required to fill the symbol table.
+  DataSharingProcessor dsp(converter, semaCtx, item->clauses, eval,
+                           /*shouldCollectPreDeterminedSymbols=*/true,
+                           /*useDelayedPrivatization=*/false, symTable);
+  dsp.processStep1();
+
+  // Emit the associated loop
+  auto canonLoop =
+      genCanonicalLoopOp(converter, symTable, semaCtx, eval, loc, queue, item,
+                         iv, llvm::omp::Directive::OMPD_unroll, dsp);
+
+  // Apply unrolling to it
+  auto cli = canonLoop.getCli();
+  firOpBuilder.create<mlir::omp::UnrollHeuristicOp>(loc, cli);
+}
+
 static mlir::omp::MaskedOp
 genMaskedOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
             lower::StatementContext &stmtCtx,
@@ -3516,12 +3671,9 @@ static void genOMPDispatch(lower::AbstractConverter &converter,
     newOp = genTeamsOp(converter, symTable, stmtCtx, semaCtx, eval, loc, queue,
                        item);
     break;
-  case llvm::omp::Directive::OMPD_tile:
-  case llvm::omp::Directive::OMPD_unroll: {
-    unsigned version = semaCtx.langOptions().OpenMPVersion;
-    TODO(loc, "Unhandled loop directive (" +
-                  llvm::omp::getOpenMPDirectiveName(dir, version) + ")");
-  }
+  case llvm::omp::Directive::OMPD_unroll:
+    genUnrollOp(converter, symTable, stmtCtx, semaCtx, eval, loc, queue, item);
+    break;
   // case llvm::omp::Directive::OMPD_workdistribute:
   case llvm::omp::Directive::OMPD_workshare:
     newOp = genWorkshareOp(converter, symTable, stmtCtx, semaCtx, eval, loc,