[flang][hlfir] Handle intrinsic subroutines

[jeanPerier]

Summary

The code did not propagate the result optionality for subroutine.
Make the result of genIntrinsicRef optional.

[clementval]

LGTM

flang/lib/Lower/ConvertCall.cpp

genUserCall(PreparedActualArguments &loweredActuals,
   if (!fir::getBase(result))
     return std::nullopt; // subroutine call.
   // TODO: "move" non pointer results into hlfir.expr.
   return extendedValueToHlfirEntity(loc, builder, result, ".tmp.func_result");
 }
 
 /// Lower calls to intrinsic procedures with actual arguments that have been
 /// pre-lowered but have not yet been prepared according to the interface.
-static hlfir::EntityWithAttributes genIntrinsicRefCore(
+static std::optional<hlfir::EntityWithAttributes> genIntrinsicRefCore(
     PreparedActualArguments &loweredActuals,
     const Fortran::evaluate::SpecificIntrinsic &intrinsic,
     const Fortran::lower::IntrinsicArgumentLoweringRules *argLowering,
     CallContext &callContext) {
   llvm::SmallVector<fir::ExtendedValue> operands;
   auto &stmtCtx = callContext.stmtCtx;
   auto &converter = callContext.converter;
   fir::FirOpBuilder &builder = callContext.getBuilder();
static std::optional<hlfir::EntityWithAttributes> genIntrinsicRefCore(
   // procedure returning an array.
   std::optional<mlir::Type> scalarResultType;
   if (callContext.resultType)
     scalarResultType = hlfir::getFortranElementType(*callContext.resultType);
   // Let the intrinsic library lower the intrinsic procedure call.
   auto [resultExv, mustBeFreed] = Fortran::lower::genIntrinsicCall(
       callContext.getBuilder(), loc, intrinsic.name, scalarResultType,
       operands);
+  if (!fir::getBase(resultExv))
+    return std::nullopt;
   hlfir::EntityWithAttributes resultEntity = extendedValueToHlfirEntity(
       loc, builder, resultExv, ".tmp.intrinsic_result");
   // Move result into memory into an hlfir.expr since they are immutable from
   // that point, and the result storage is some temp.
   if (!fir::isa_trivial(resultEntity.getType())) {
     hlfir::AsExprOp asExpr;
     // Character/Derived MERGE lowering returns one of its argument address
     // (this is the only intrinsic implemented in that way so far). The
genIsPresentIfArgMaybeAbsent(mlir::Location loc, hlfir::Entity actual,
   // May fall into the category above if the allocatable is not optional.
 
   // Passing an optional to an optional.
   return builder.create<fir::IsPresentOp>(loc, builder.getI1Type(), actual)
       .getResult();
 }
 
 /// Lower an intrinsic procedure reference.
-static hlfir::EntityWithAttributes
+static std::optional<hlfir::EntityWithAttributes>
 genIntrinsicRef(const Fortran::evaluate::SpecificIntrinsic &intrinsic,
                 CallContext &callContext) {
   mlir::Location loc = callContext.loc;
   auto &converter = callContext.converter;
   if (Fortran::lower::intrinsicRequiresCustomOptionalHandling(
           callContext.procRef, intrinsic, converter))
     TODO(loc, "special cases of intrinsic with optional arguments");
 
genIntrinsicRef(const Fortran::evaluate::SpecificIntrinsic &intrinsic,
 
   if (callContext.isElementalProcWithArrayArgs()) {
     // All intrinsic elemental functions are pure.
     const bool isFunction = callContext.resultType.has_value();
     return ElementalIntrinsicCallBuilder{intrinsic, argLowering, isFunction}
         .genElementalCall(loweredActuals, /*isImpure=*/!isFunction, callContext)
         .value();
   }
-  hlfir::EntityWithAttributes result =
+  std::optional<hlfir::EntityWithAttributes> result =
       genIntrinsicRefCore(loweredActuals, intrinsic, argLowering, callContext);
-  if (result.getType().isa<hlfir::ExprType>()) {
+  if (result && result->getType().isa<hlfir::ExprType>()) {
     fir::FirOpBuilder *bldr = &callContext.getBuilder();
     callContext.stmtCtx.attachCleanup(
-        [=]() { bldr->create<hlfir::DestroyOp>(loc, result); });
+        [=]() { bldr->create<hlfir::DestroyOp>(loc, *result); });
   }
   return result;
 }
 
 /// Main entry point to lower procedure references, regardless of what they are.
 static std::optional<hlfir::EntityWithAttributes>
 genProcedureRef(CallContext &callContext) {
   mlir::Location loc = callContext.loc;

flang/test/Lower/HLFIR/intrinsic-subroutines.f90

+! Test lowering of intrinsic subroutines to HLFIR what matters here
+! is not to test each subroutine, but to check how their
+! lowering interfaces with the rest of lowering.
+! RUN: bbc -emit-fir -hlfir -o - %s | FileCheck %s
+
+subroutine test_subroutine(x)
+ real :: x
+ call cpu_time(x)
+end subroutine
+! CHECK-LABEL: func.func @_QPtest_subroutine(
+! CHECK:  %[[VAL_1:.*]]:2 = hlfir.declare %{{.*}}
+! CHECK:  %[[VAL_2:.*]] = fir.call @_FortranACpuTime() fastmath<contract> : () -> f64
+! CHECK:  %[[VAL_3:.*]] = fir.convert %[[VAL_2]] : (f64) -> f32
+! CHECK:  fir.store %[[VAL_3]] to %[[VAL_1]]#1 : !fir.ref<f32>