[flang][lowering] Add support for lowering of the `ibset` intrinsic

[awarzynski]

Summary

This patch adds support for lowering of the ibset intrinsic from Fortran
to the FIR dialect of MLIR.

This is part of the upstreaming effort from the fir-dev branch in [1].

[1] https://github.com/flang-compiler/f18-llvm-project

Co-authored-by: Jean Perier <[e-mail]>
Co-authored-by: Valentin Clement <[e-mail]>
Co-authored-by: V Donaldson <[e-mail]>

flang/lib/Lower/IntrinsicCall.cpp

struct IntrinsicLibrary {
   void genCpuTime(llvm::ArrayRef<fir::ExtendedValue>);
   void genDateAndTime(llvm::ArrayRef<fir::ExtendedValue>);
   template <Extremum, ExtremumBehavior>
   mlir::Value genExtremum(mlir::Type, llvm::ArrayRef<mlir::Value>);
   /// Lowering for the IAND intrinsic. The IAND intrinsic expects two arguments
   /// in the llvm::ArrayRef.
   mlir::Value genIand(mlir::Type, llvm::ArrayRef<mlir::Value>);
   mlir::Value genIbits(mlir::Type, llvm::ArrayRef<mlir::Value>);
+  mlir::Value genIbset(mlir::Type, llvm::ArrayRef<mlir::Value>);
   fir::ExtendedValue genLbound(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genNull(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genLen(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genLenTrim(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genMaxloc(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genMaxval(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genMinloc(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   fir::ExtendedValue genMinval(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
static constexpr IntrinsicHandler handlers[]{
      /*isElemental=*/false},
     {"dim", &I::genDim},
     {"dot_product",
      &I::genDotProduct,
      {{{"vector_a", asBox}, {"vector_b", asBox}}},
      /*isElemental=*/false},
     {"iand", &I::genIand},
     {"ibits", &I::genIbits},
+    {"ibset", &I::genIbset},
     {"len",
      &I::genLen,
      {{{"string", asInquired}, {"kind", asValue}}},
      /*isElemental=*/false},
     {"len_trim", &I::genLenTrim},
     {"lge", &I::genCharacterCompare<mlir::arith::CmpIPredicate::sge>},
     {"lgt", &I::genCharacterCompare<mlir::arith::CmpIPredicate::sgt>},
     {"lle", &I::genCharacterCompare<mlir::arith::CmpIPredicate::sle>},
mlir::Value IntrinsicLibrary::genIbits(mlir::Type resultType,
   auto mask = builder.create<mlir::arith::ShRUIOp>(loc, ones, shiftCount);
   auto res1 = builder.create<mlir::arith::ShRSIOp>(loc, args[0], pos);
   auto res2 = builder.create<mlir::arith::AndIOp>(loc, res1, mask);
   auto lenIsZero = builder.create<mlir::arith::CmpIOp>(
       loc, mlir::arith::CmpIPredicate::eq, len, zero);
   return builder.create<mlir::arith::SelectOp>(loc, lenIsZero, zero, res2);
 }
 
+// IBSET
+mlir::Value IntrinsicLibrary::genIbset(mlir::Type resultType,
+                                       llvm::ArrayRef<mlir::Value> args) {
+  // A conformant IBSET(I,POS) call satisfies:
+  //     POS >= 0
+  //     POS < BIT_SIZE(I)
+  // Return:  I | (1 << POS)
+  assert(args.size() == 2);
+  mlir::Value pos = builder.createConvert(loc, resultType, args[1]);
+  mlir::Value one = builder.createIntegerConstant(loc, resultType, 1);
+  auto mask = builder.create<mlir::arith::ShLIOp>(loc, one, pos);
+  return builder.create<mlir::arith::OrIOp>(loc, args[0], mask);
+}
+
 // LEN
 // Note that this is only used for an unrestricted intrinsic LEN call.
 // Other uses of LEN are rewritten as descriptor inquiries by the front-end.
 fir::ExtendedValue
 IntrinsicLibrary::genLen(mlir::Type resultType,
                          llvm::ArrayRef<fir::ExtendedValue> args) {
   // Optional KIND argument reflected in result type and otherwise ignored.
   assert(args.size() == 1 || args.size() == 2);

flang/test/Lower/Intrinsics/ibset.f90

+! RUN: bbc -emit-fir %s -o - | FileCheck %s
+! RUN: %flang_fc1 -emit-fir %s -o - | FileCheck %s
+
+! CHECK-LABEL: ibset_test
+function ibset_test(i, j)
+  ! CHECK-DAG: %[[result:.*]] = fir.alloca i32 {bindc_name = "ibset_test"
+  ! CHECK-DAG: %[[i:.*]] = fir.load %arg0 : !fir.ref<i32>
+  ! CHECK-DAG: %[[j:.*]] = fir.load %arg1 : !fir.ref<i32>
+  ! CHECK-DAG: %[[VAL_5:.*]] = arith.constant 1 : i32
+  ! CHECK: %[[VAL_6:.*]] = arith.shli %[[VAL_5]], %[[j]] : i32
+  ! CHECK: %[[VAL_7:.*]] = arith.ori %[[i]], %[[VAL_6]] : i32
+  ! CHECK: fir.store %[[VAL_7]] to %[[result]] : !fir.ref<i32>
+  ! CHECK: %[[VAL_8:.*]] = fir.load %[[result]] : !fir.ref<i32>
+  ! CHECK: return %[[VAL_8]] : i32
+  ibset_test = ibset(i, j)
+end
+