[flang] Lower present intrinsic

This patch adds lowering for the `present` intrinsic.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: jeanPerier

Differential Revision: https://reviews.llvm.org/D121884

Co-authored-by: Jean Perier <jperier@nvidia.com>

flang/lib/Lower/IntrinsicCall.cpp

@@ -485,6 +485,7 @@ struct IntrinsicLibrary {
   mlir::Value genNot(mlir::Type, llvm::ArrayRef<mlir::Value>);
   fir::ExtendedValue genNull(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genPack(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
+  fir::ExtendedValue genPresent(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genProduct(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   void genRandomInit(llvm::ArrayRef<fir::ExtendedValue>);
   void genRandomNumber(llvm::ArrayRef<fir::ExtendedValue>);
@@ -726,6 +727,10 @@ static constexpr IntrinsicHandler handlers[]{
        {"mask", asBox},
        {"vector", asBox, handleDynamicOptional}}},
      /*isElemental=*/false},
+    {"present",
+     &I::genPresent,
+     {{{"a", asInquired}}},
+     /*isElemental=*/false},
     {"product",
      &I::genProduct,
      {{{"array", asBox},
@@ -2563,6 +2568,15 @@ IntrinsicLibrary::genPack(mlir::Type resultType,
                            "unexpected result for PACK");
 }
 
+// PRESENT
+fir::ExtendedValue
+IntrinsicLibrary::genPresent(mlir::Type,
+                             llvm::ArrayRef<fir::ExtendedValue> args) {
+  assert(args.size() == 1);
+  return builder.create<fir::IsPresentOp>(loc, builder.getI1Type(),
+                                          fir::getBase(args[0]));
+}
+
 // PRODUCT
 fir::ExtendedValue
 IntrinsicLibrary::genProduct(mlir::Type resultType,

flang/test/Lower/Intrinsics/present.f90

@@ -0,0 +1,10 @@
+! RUN: bbc -emit-fir %s -o - | FileCheck %s
+
+! CHECK-LABEL: present_test
+! CHECK-SAME: %[[arg0:[^:]+]]: !fir.box<!fir.array<?xi32>>
+subroutine present_test(a)
+  integer, optional :: a(:)
+
+  if (present(a)) print *,a
+  ! CHECK: %{{.*}} = fir.is_present %[[arg0]] : (!fir.box<!fir.array<?xi32>>) -> i1
+end subroutine