[flang] implement function form of SYSTEM intrinsic

SYSTEM is a gfortran extension which we already supported in subroutine
form. Gfortran also allows it to be called as a function, which was
requested by a user
https://discourse.llvm.org/t/unresolved-externals-with-appendend-underscore/83305/4

Author: tblah

flang/include/flang/Optimizer/Builder/IntrinsicCall.h

@@ -395,7 +395,8 @@ struct IntrinsicLibrary {
   fir::ExtendedValue genSum(mlir::Type, llvm::ArrayRef<fir::ExtendedValue>);
   void genSignalSubroutine(llvm::ArrayRef<fir::ExtendedValue>);
   void genSleep(llvm::ArrayRef<fir::ExtendedValue>);
-  void genSystem(mlir::ArrayRef<fir::ExtendedValue> args);
+  fir::ExtendedValue genSystem(std::optional<mlir::Type>,
+                               mlir::ArrayRef<fir::ExtendedValue> args);
   void genSystemClock(llvm::ArrayRef<fir::ExtendedValue>);
   mlir::Value genTand(mlir::Type, llvm::ArrayRef<mlir::Value>);
   mlir::Value genTrailz(mlir::Type, llvm::ArrayRef<mlir::Value>);

flang/lib/Evaluate/intrinsics.cpp

@@ -884,6 +884,8 @@ static const IntrinsicInterface genericIntrinsicFunction[]{
         IntrinsicClass::transformationalFunction},
     {"sum", {{"array", SameNumeric, Rank::array}, MissingDIM, OptionalMASK},
         SameNumeric, Rank::scalar, IntrinsicClass::transformationalFunction},
+    {"system", {{"command", DefaultChar, Rank::scalar}}, DefaultInt,
+        Rank::scalar},
     {"tan", {{"x", SameFloating}}, SameFloating},
     {"tand", {{"x", SameFloating}}, SameFloating},
     {"tanh", {{"x", SameFloating}}, SameFloating},
@@ -2640,7 +2642,7 @@ bool IntrinsicProcTable::Implementation::IsDualIntrinsic(
   // Collection for some intrinsics with function and subroutine form,
   // in order to pass the semantic check.
   static const std::string dualIntrinsic[]{
-      {"etime"s}, {"getcwd"s}, {"rename"s}, {"second"s}};
+      {"etime"s}, {"getcwd"s}, {"rename"s}, {"second"s}, {"system"s}};
 
   return llvm::is_contained(dualIntrinsic, name);
 }

flang/lib/Optimizer/Builder/IntrinsicCall.cpp

@@ -7280,12 +7280,22 @@ IntrinsicLibrary::genSum(mlir::Type resultType,
 }
 
 // SYSTEM
-void IntrinsicLibrary::genSystem(llvm::ArrayRef<fir::ExtendedValue> args) {
-  assert(args.size() == 2);
+fir::ExtendedValue
+IntrinsicLibrary::genSystem(std::optional<mlir::Type> resultType,
+                            llvm::ArrayRef<fir::ExtendedValue> args) {
+  assert((!resultType && (args.size() == 2)) ||
+         (resultType && (args.size() == 1)));
   mlir::Value command = fir::getBase(args[0]);
-  const fir::ExtendedValue &exitstat = args[1];
   assert(command && "expected COMMAND parameter");
 
+  fir::ExtendedValue exitstat;
+  if (resultType) {
+    mlir::Value tmp = builder.createTemporary(loc, *resultType);
+    exitstat = builder.createBox(loc, tmp);
+  } else {
+    exitstat = args[1];
+  }
+
   mlir::Type boxNoneTy = fir::BoxType::get(builder.getNoneType());
 
   mlir::Value waitBool = builder.createBool(loc, true);
@@ -7307,6 +7317,12 @@ void IntrinsicLibrary::genSystem(llvm::ArrayRef<fir::ExtendedValue> args) {
 
   fir::runtime::genExecuteCommandLine(builder, loc, command, waitBool,
                                       exitstatBox, cmdstatBox, cmdmsgBox);
+
+  if (resultType) {
+    mlir::Value exitstatAddr = builder.create<fir::BoxAddrOp>(loc, exitstatBox);
+    return builder.create<fir::LoadOp>(loc, fir::getBase(exitstatAddr));
+  }
+  return {};
 }
 
 // SYSTEM_CLOCK

flang/test/Lower/Intrinsics/system.f90

@@ -51,3 +51,35 @@ subroutine only_command(command)
 ! CHECK-NEXT:   return
 ! CHECK-NEXT:    }
 end subroutine only_command
+
+! CHECK-LABEL: func.func @_QPas_function(
+! CHECK-SAME:    %[[commandArg:.*]]: !fir.boxchar<1> {fir.bindc_name = "command"}
+subroutine as_function(command)
+CHARACTER(*) :: command
+INTEGER :: exitstat
+exitstat = system(command)
+end subroutine
+! CHECK-NEXT:   %[[cmdstatVal:.*]] = fir.alloca i16
+! CHECK-NEXT:   %[[RETVAL:.*]] = fir.alloca i32
+! CHECK-NEXT:   %[[DSCOPE:.*]] = fir.dummy_scope : !fir.dscope
+! CHECK-NEXT:   %[[commandUnbox:.*]]:2 = fir.unboxchar %[[commandArg]] : (!fir.boxchar<1>) -> (!fir.ref<!fir.char<1,?>>, index)
+! CHECK-NEXT:   %[[commandDeclare:.*]]:2 = hlfir.declare %[[commandUnbox]]#0 typeparams %[[commandUnbox]]#1 dummy_scope %[[DSCOPE]] {uniq_name = "_QFas_functionEcommand"} : (!fir.ref<!fir.char<1,?>>, index, !fir.dscope) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK-NEXT:   %[[EXITSTAT_ALLOC:.*]] = fir.alloca i32
+! CHECK-NEXT:   %[[exitstatDeclare:.*]]:2 = hlfir.declare %[[EXITSTAT_ALLOC]] {uniq_name = "_QFas_functionEexitstat"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+! CHECK-NEXT:   %[[commandBox:.*]] = fir.embox %[[commandDeclare]]#1 typeparams %[[commandUnbox]]#1 : (!fir.ref<!fir.char<1,?>>, index) -> !fir.box<!fir.char<1,?>>
+! CHECK-NEXT:   %[[exitstatBox:.*]] = fir.embox %[[RETVAL]] : (!fir.ref<i32>) -> !fir.box<i32>
+! CHECK-NEXT:   %[[true:.*]] = arith.constant true
+! CHECK-NEXT:   %[[c0_i16:.*]] = arith.constant 0 : i16
+! CHECK-NEXT:   fir.store %[[c0_i16]] to %[[cmdstatVal]] : !fir.ref<i16>
+! CHECK-NEXT:   %[[cmdstatBox:.*]] = fir.embox %[[cmdstatVal]] : (!fir.ref<i16>) -> !fir.box<i16>
+! CHECK-NEXT:   %[[absentBox:.*]] = fir.absent !fir.box<none>
+! CHECK:        %[[LINE_NO:.*]] = arith.constant {{.*}} : i32
+! CHECK-NEXT:   %[[command:.*]] = fir.convert %[[commandBox]] : (!fir.box<!fir.char<1,?>>) -> !fir.box<none>
+! CHECK-NEXT:   %[[exitstat:.*]] = fir.convert %[[exitstatBox]] : (!fir.box<i32>) -> !fir.box<none>
+! CHECK-NEXT:   %[[cmdstat:.*]] = fir.convert %[[cmdstatBox]] : (!fir.box<i16>) -> !fir.box<none>
+! CHECK:        %[[VAL_13:.*]] = fir.call @_FortranAExecuteCommandLine(%[[command]], %[[true]], %[[exitstat]], %[[cmdstat]], %[[absentBox]], %[[VAL_12:.*]], %[[LINE_NO]]) fastmath<contract> : (!fir.box<none>, i1, !fir.box<none>, !fir.box<none>, !fir.box<none>, !fir.ref<i8>, i32) -> none
+! CHECK-NEXT:   %[[RET_ADDR:.*]] = fir.box_addr %[[exitstatBox]] : (!fir.box<i32>) -> !fir.ref<i32>
+! CHECK-NEXT:   %[[RET:.*]] = fir.load %[[RET_ADDR]] : !fir.ref<i32>
+! CHECK-NEXT:   hlfir.assign %[[RET]] to %[[exitstatDeclare]]#0 : i32, !fir.ref<i32>
+! CHECK-NEXT:   return
+! CHECK-NEXT:  }