[flang][hlfir] `hlfir.char_extremum` lowering

[cabreraam]

Summary

This patch implements the lowering for the hlfir.char_extremum operation.

Discussion for this patch can be found in the draft patch here. The reason
for not promoting this draft to a true patch for review was because I needed to separate the op
definition/codegen and lowering into two separate patches, as preferred by @jeanPerier.

Depends on D152474

[vzakhari]

Thank you for working on this! There seems to be missing dependency on the patch that defines the operation.

flang/lib/Lower/ConvertCall.cpp

1369

Isn't Fortran::lower::convertToValue more suitable here?

[cabreraam]

In D152475#4407425, @vzakhari wrote:

Thank you for working on this! There seems to be missing dependency on the patch that defines the operation.

Yes! Here is the patch that this current patch depends on.
Is there a better way to show the dependency of this patch on the other patch that I linked?

Just FYI, the buildbot fails on this patch because of the dependency of D152474.

[vzakhari]

In D152475#4407541, @cabreraam wrote:

In D152475#4407425, @vzakhari wrote:

Thank you for working on this! There seems to be missing dependency on the patch that defines the operation.

Yes! Here is the patch that this current patch depends on.
Is there a better way to show the dependency of this patch on the other patch that I linked?

Just FYI, the buildbot fails on this patch because of the dependency of D152474.

The easiest way to add the dependency is to put Depends on D#### into the summary above. Next time you can do it right at the creation of the new differential, so that the pre-commit testing kicks in with the right dependencies.

[vzakhari]

See example here: https://reviews.llvm.org/D152493

[tschuett]

Alternatively, you will find Edit Related Revisions... at the top right.

[tblah]

LGTM once other reviewers are happy

[cabreraam]

flang/lib/Lower/ConvertCall.cpp

1369

I see that convertToValue is used in a different place in ConvertCall.cpp, i.e., in genIntrinsicRefCore for a similar reason to what I'm doing here, so I take your point @vzakhari. My only thought is that this lambda function is expected to return SmallVector<mlir::Value> whereas convertToValue would necessitate SmallVector<fir::ExtendedValue> since convertToValue returns fir::ExtendedValue. @tblah or @jeanPerier, care to weigh in?

[tblah]

flang/lib/Lower/ConvertCall.cpp

1369

As of https://reviews.llvm.org/D153252, loadTrivialScalar will just be a convertToValue then converting it to an extended value. I think loadTrivialScalar is fine here.

[jeanPerier]

Thanks, LGTM!

flang/lib/Lower/ConvertCall.cpp

for (size_t i = 0; i < loweredActuals.size(); ++i) {
       std::optional<PreparedActualArgument> arg = loweredActuals[i];
       if (!arg) {
         operands.emplace_back();
         continue;
       }
       hlfir::Entity actual = arg->getOriginalActual();
       mlir::Value valArg;
 
+      // if intrinsic handler has no lowering rules
+      if (!argLowering) {
+        valArg = hlfir::loadTrivialScalar(loc, builder, actual);
+      } else {
         fir::ArgLoweringRule argRules =
             fir::lowerIntrinsicArgumentAs(*argLowering, i);
         if (!argRules.handleDynamicOptional &&
             argRules.lowerAs != fir::LowerIntrinsicArgAs::Inquired)
           valArg = hlfir::derefPointersAndAllocatables(loc, builder, actual);
         else
           valArg = actual.getBase();
+      }
 
       operands.emplace_back(valArg);
     }
     return operands;
   };
 
   auto computeResultType = [&](mlir::Value argArray,
                                mlir::Type stmtResultType) -> mlir::Type {
if (dim)
       dim = hlfir::loadTrivialScalar(loc, builder, hlfir::Entity{dim});
     mlir::Value kind = operands[2];
     mlir::Type resultTy = computeResultType(array, *callContext.resultType);
     hlfir::CountOp countOp =
         builder.create<hlfir::CountOp>(loc, resultTy, array, dim, kind);
     return {hlfir::EntityWithAttributes{countOp.getResult()}};
   }
 
+  if ((intrinsicName == "min" || intrinsicName == "max") &&
+      hlfir::getFortranElementType(callContext.resultType.value())
+          .isa<fir::CharacterType>()) {
+    llvm::SmallVector<mlir::Value> operands = getOperandVector(loweredActuals);
+    assert(operands.size() >= 2);
+
+    hlfir::CharExtremumPredicate pred = (intrinsicName == "min")
+                                            ? hlfir::CharExtremumPredicate::min
+                                            : hlfir::CharExtremumPredicate::max;
+    hlfir::CharExtremumOp charExtremumOp =
+        builder.create<hlfir::CharExtremumOp>(loc, pred,
+                                              mlir::ValueRange{operands});
+    return {hlfir::EntityWithAttributes{charExtremumOp.getResult()}};
+  }
+
   // TODO add hlfir operations for other transformational intrinsics here
 
   // fallback to calling the intrinsic via fir.call
   return genIntrinsicRefCore(loweredActuals, intrinsic, argLowering,
                              callContext);
 }
 
 namespace {

flang/test/Lower/HLFIR/char_extremum.f03

+! Test lowering of the max and min intrinsics on character types to HLFIR
+! RUN: bbc -emit-hlfir -o - %s 2>&1 | FileCheck %s
+
+subroutine max1(c1, c2, c3)
+  character(*) :: c1, c2, c3
+  c1 = max(c2,c3)
+end subroutine
+
+! CHECK-LABEL: func.func @_QPmax1
+! CHECK:  %[[VAL_0:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_1:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_0]]#0 typeparams %[[VAL_0]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_2:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_3:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_2]]#0 typeparams %[[VAL_2]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_4:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_5:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_4]]#0 typeparams %[[VAL_4]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_6:[a-zA-Z0-9_]*]] = hlfir.char_extremum max, %[[VAL_3]]#0, %[[VAL_5]]#0 : (!fir.boxchar<1>, !fir.boxchar<1>) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK:  hlfir.assign %[[VAL_6]] to %[[VAL_1]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.boxchar<1>
+! CHECK:  hlfir.destroy %[[VAL_6]] : !hlfir.expr<!fir.char<1,?>>
+
+subroutine min1(c1, c2, c3)
+  character(*) :: c1, c2, c3
+  c1 = min(c2,c3)
+end subroutine
+! CHECK-LABEL: func.func @_QPmin1
+! CHECK:  %[[VAL_0:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_1:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_0]]#0 typeparams %[[VAL_0]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_2:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_3:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_2]]#0 typeparams %[[VAL_2]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_4:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_5:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_4]]#0 typeparams %[[VAL_4]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_6:[a-zA-Z0-9_]*]] = hlfir.char_extremum min, %[[VAL_3]]#0, %[[VAL_5]]#0 : (!fir.boxchar<1>, !fir.boxchar<1>) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK:  hlfir.assign %[[VAL_6]] to %[[VAL_1]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.boxchar<1>
+! CHECK:  hlfir.destroy %[[VAL_6]] : !hlfir.expr<!fir.char<1,?>>
+! CHECK:  return
+
+subroutine max2(c1, c2, c3)
+  character(*) :: c1(100)
+  character :: c2(100)*10, c3(100)*20
+  c1(1) = max(c2(1),c3(1))
+end subroutine
+! CHECK-LABEL:  func.func @_QPmax2
+! CHECK:  %[[VAL_0:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_1:[a-zA-Z0-9_]*]] = fir.convert %[[VAL_0]]#0 : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.array<100x!fir.char<1,?>>>
+! CHECK:  %[[VAL_C100:[a-zA-Z0-9_]*]] = arith.constant 100 : index
+! CHECK:  %[[VAL_2:[a-zA-Z0-9_]*]]  = fir.shape %[[VAL_C100]] : (index) -> !fir.shape<1>
+! CHECK:  %[[VAL_3:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_1]](%[[VAL_2]]) typeparams %[[VAL_0]]#1 {{.*}} : (!fir.ref<!fir.array<100x!fir.char<1,?>>>, !fir.shape<1>, index) -> (!fir.box<!fir.array<100x!fir.char<1,?>>>, !fir.ref<!fir.array<100x!fir.char<1,?>>>)
+! CHECK:  %[[VAL_4:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_C10:[a-zA-Z0-9_]*]] = arith.constant 10 : index
+! CHECK:  %[[VAL_5:[a-zA-Z0-9_]*]] = fir.convert %[[VAL_4]]#0 : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.array<100x!fir.char<1,10>>>
+! CHECK:  %[[VAL_C100_0:[a-zA-Z0-9_]*]] = arith.constant 100 : index
+! CHECK:  %[[VAL_6:[a-zA-Z0-9_]*]] = fir.shape %[[VAL_C100_0]] : (index) -> !fir.shape<1>
+! CHECK:  %[[VAL_7:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_5]](%[[VAL_6]]) typeparams %[[VAL_C10]] {{.*}} : (!fir.ref<!fir.array<100x!fir.char<1,10>>>, !fir.shape<1>, index) -> (!fir.ref<!fir.array<100x!fir.char<1,10>>>, !fir.ref<!fir.array<100x!fir.char<1,10>>>)
+! CHECK:  %[[VAL_8:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %{{.*}} : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_C20:[a-zA-Z0-9_]*]] = arith.constant 20 : index
+! CHECK:  %[[VAL_9:[a-zA-Z0-9_]*]] = fir.convert %[[VAL_8]]#0 : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.array<100x!fir.char<1,20>>>
+! CHECK:  %[[VAL_C100_1:[a-zA-Z0-9_]*]] = arith.constant 100 : index
+! CHECK:  %[[VAL_10:[a-zA-Z0-9_]*]] = fir.shape %[[VAL_C100_1]] : (index) -> !fir.shape<1>
+! CHECK:  %[[VAL_11:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_9]](%[[VAL_10]]) typeparams %[[VAL_C20]] {{.*}} : (!fir.ref<!fir.array<100x!fir.char<1,20>>>, !fir.shape<1>, index) -> (!fir.ref<!fir.array<100x!fir.char<1,20>>>, !fir.ref<!fir.array<100x!fir.char<1,20>>>)
+! CHECK:  %[[VAL_C1:[a-zA-Z0-9_]*]] = arith.constant 1 : index
+! CHECK:  %[[VAL_12:[a-zA-Z0-9_]*]] = hlfir.designate %[[VAL_7]]#0 (%[[VAL_C1]])  typeparams %[[VAL_C10]] : (!fir.ref<!fir.array<100x!fir.char<1,10>>>, index, index) -> !fir.ref<!fir.char<1,10>>
+! CHECK:  %[[VAL_C1_2:[a-zA-Z0-9_]*]] = arith.constant 1 : index
+! CHECK:  %[[VAL_13:[a-zA-Z0-9_]*]] = hlfir.designate %[[VAL_11]]#0 (%[[VAL_C1_2]])  typeparams %[[VAL_C20]] : (!fir.ref<!fir.array<100x!fir.char<1,20>>>, index, index) -> !fir.ref<!fir.char<1,20>>
+! CHECK:  %[[VAL_14:[a-zA-Z0-9_]*]] = hlfir.char_extremum max, %[[VAL_12]], %[[VAL_13]] : (!fir.ref<!fir.char<1,10>>, !fir.ref<!fir.char<1,20>>) -> !hlfir.expr<!fir.char<1,20>>
+! CHECK:  %c1_3 = arith.constant 1 : index
+! CHECK:  %[[VAL_15:[a-zA-Z0-9_]*]] = hlfir.designate %[[VAL_3]]#0 (%c1_3)  typeparams %[[VAL_0]]#1 : (!fir.box<!fir.array<100x!fir.char<1,?>>>, index, index) -> !fir.boxchar<1>
+! CHECK:  hlfir.assign %[[VAL_14]] to %[[VAL_15]] : !hlfir.expr<!fir.char<1,20>>, !fir.boxchar<1>
+! CHECK:  hlfir.destroy %[[VAL_14]] : !hlfir.expr<!fir.char<1,20>>
+
+subroutine min2(c1, c2, c3)
+  character(*) :: c1(100)
+  character :: c2(100)*10, c3(100)*20
+  c1(1) = min(c2(1),c3(1))
+end subroutine
+! CHECK-LABEL: func.func @_QPmin2
+! CHECK:  %[[VAL_0:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_1:[a-zA-Z0-9_]*]] = fir.convert %[[VAL_0]]#0 : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.array<100x!fir.char<1,?>>>
+! CHECK:  %[[VAL_C100:[a-zA-Z0-9_]*]] = arith.constant 100 : index
+! CHECK:  %[[VAL_2:[a-zA-Z0-9_]*]] = fir.shape %[[VAL_C100]] : (index) -> !fir.shape<1>
+! CHECK:  %[[VAL_3:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_1]](%[[VAL_2]]) typeparams %[[VAL_0]]#1 {{.*}} : (!fir.ref<!fir.array<100x!fir.char<1,?>>>, !fir.shape<1>, index) -> (!fir.box<!fir.array<100x!fir.char<1,?>>>, !fir.ref<!fir.array<100x!fir.char<1,?>>>)
+! CHECK:  %[[VAL_4:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg1 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_C10:[a-zA-Z0-9_]*]] = arith.constant 10 : index
+! CHECK:  %[[VAL_5:[a-zA-Z0-9_]*]] = fir.convert %[[VAL_4]]#0 : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.array<100x!fir.char<1,10>>>
+! CHECK:  %[[VAL_C100_0:[a-zA-Z0-9_]*]] = arith.constant 100 : index
+! CHECK:  %[[VAL_6:[a-zA-Z0-9_]*]] = fir.shape %[[VAL_C100_0]] : (index) -> !fir.shape<1>
+! CHECK:  %[[VAL_7:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_5]](%[[VAL_6]]) typeparams %[[VAL_C10]] {{.*}} : (!fir.ref<!fir.array<100x!fir.char<1,10>>>, !fir.shape<1>, index) -> (!fir.ref<!fir.array<100x!fir.char<1,10>>>, !fir.ref<!fir.array<100x!fir.char<1,10>>>)
+! CHECK:  %[[VAL_8:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg2 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_C20:[a-zA-Z0-9_]*]] = arith.constant 20 : index
+! CHECK:  %[[VAL_C9:[a-zA-Z0-9_]*]] = fir.convert %[[VAL_8]]#0 : (!fir.ref<!fir.char<1,?>>) -> !fir.ref<!fir.array<100x!fir.char<1,20>>>
+! CHECK:  %[[VAL_C100_1:[a-zA-Z0-9_]*]] = arith.constant 100 : index
+! CHECK:  %[[VAL_10:[a-zA-Z0-9_]*]] = fir.shape %[[VAL_C100_1]] : (index) -> !fir.shape<1>
+! CHECK:  %[[VAL_11:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_C9]](%[[VAL_10]]) typeparams %[[VAL_C20]] {{.*}} : (!fir.ref<!fir.array<100x!fir.char<1,20>>>, !fir.shape<1>, index) -> (!fir.ref<!fir.array<100x!fir.char<1,20>>>, !fir.ref<!fir.array<100x!fir.char<1,20>>>)
+! CHECK:  %[[VAL_C1:[a-zA-Z0-9_]*]] = arith.constant 1 : index
+! CHECK:  %[[VAL_12:[a-zA-Z0-9_]*]] = hlfir.designate %[[VAL_7]]#0 (%[[VAL_C1]])  typeparams %[[VAL_C10]] : (!fir.ref<!fir.array<100x!fir.char<1,10>>>, index, index) -> !fir.ref<!fir.char<1,10>>
+! CHECK:  %[[VAL_C1_2:[a-zA-Z0-9_]*]] = arith.constant 1 : index
+! CHECK:  %[[VAL_13:[a-zA-Z0-9_]*]] = hlfir.designate %[[VAL_11]]#0 (%[[VAL_C1_2]])  typeparams %[[VAL_C20]] : (!fir.ref<!fir.array<100x!fir.char<1,20>>>, index, index) -> !fir.ref<!fir.char<1,20>>
+! CHECK:  %[[VAL_14:[a-zA-Z0-9_]*]] = hlfir.char_extremum min, %[[VAL_12]], %[[VAL_13]] : (!fir.ref<!fir.char<1,10>>, !fir.ref<!fir.char<1,20>>) -> !hlfir.expr<!fir.char<1,20>>
+! CHECK:  %[[VAL_C1_3:[a-zA-Z0-9_]*]] = arith.constant 1 : index
+! CHECK:  %[[VAL_15:[a-zA-Z0-9_]*]] = hlfir.designate %[[VAL_3]]#0 (%[[VAL_C1_3]])  typeparams %[[VAL_0]]#1 : (!fir.box<!fir.array<100x!fir.char<1,?>>>, index, index) -> !fir.boxchar<1>
+! CHECK:  hlfir.assign %[[VAL_14]] to %[[VAL_15]] : !hlfir.expr<!fir.char<1,20>>, !fir.boxchar<1>
+! CHECK:  hlfir.destroy %[[VAL_14]] : !hlfir.expr<!fir.char<1,20>>
+
+subroutine max3(c1, c2, c3, c4)
+  character(*) :: c1, c2, c3, c4
+  c1 = max(c2, c3, c4)
+end subroutine
+! CHECK-LABEL: func.func @_QPmax3
+! CHECK:  %[[VAL_0:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_1:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_0]]#0 typeparams %[[VAL_0]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_2:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg1 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_3:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_2]]#0 typeparams %[[VAL_2]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_4:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg2 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_5:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_4]]#0 typeparams %[[VAL_4]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_6:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg3 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_7:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_6]]#0 typeparams %[[VAL_6]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_8:[a-zA-Z0-9_]*]] = hlfir.char_extremum max, %[[VAL_3]]#0, %[[VAL_5]]#0, %[[VAL_7]]#0 : (!fir.boxchar<1>, !fir.boxchar<1>, !fir.boxchar<1>) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK:  hlfir.assign %[[VAL_8]] to %[[VAL_1]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.boxchar<1>
+! CHECK:  hlfir.destroy %[[VAL_8]] : !hlfir.expr<!fir.char<1,?>>
+
+subroutine min3(c1, c2, c3, c4)
+  character(*) :: c1, c2, c3, c4
+  c1 = min(c2, c3, c4)
+end subroutine
+! CHECK-LABEL: func.func @_QPmin3
+! CHECK:  %[[VAL_0:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg0 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_1:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_0]]#0 typeparams %[[VAL_0]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_2:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg1 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_3:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_2]]#0 typeparams %[[VAL_2]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_4:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg2 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_5:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_4]]#0 typeparams %[[VAL_4]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_6:[a-zA-Z0-9_]*]]:2 = fir.unboxchar %arg3 : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK:  %[[VAL_7:[a-zA-Z0-9_]*]]:2 = hlfir.declare %[[VAL_6]]#0 typeparams %[[VAL_6]]#1 {{.*}} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:  %[[VAL_8:[a-zA-Z0-9_]*]] = hlfir.char_extremum min, %[[VAL_3]]#0, %[[VAL_5]]#0, %[[VAL_7]]#0 : (!fir.boxchar<1>, !fir.boxchar<1>, !fir.boxchar<1>) -> !hlfir.expr<!fir.char<1,?>>
+! CHECK:  hlfir.assign %[[VAL_8]] to %[[VAL_1]]#0 : !hlfir.expr<!fir.char<1,?>>, !fir.boxchar<1>
+! CHECK:  hlfir.destroy %[[VAL_8]] : !hlfir.expr<!fir.char<1,?>>