[flang] Add runtime interface for GET_COMMAND_ARGUMENT

[rovka]

Summary

GET_COMMAND_ARGUMENT takes a lot of optional arguments: VALUE, LENGTH,
STATUS and ERRMSG. This patch breaks up the interface into 2 different
functions:

• One for getting the LENGTH of an argument.

• One for (optionally) getting the VALUE and the ERRMSG of an argument. This returns

the STATUS, which can be easily ignored by lowering if it is missing in
the invocation.

[klausler]

environment.h is not a header for APIs.

The ERRMSG argument could be a nullable pointer argument to ArgumentValue.

[rovka]

In D108688#2965273, @klausler wrote:

environment.h is not a header for APIs.

Ok, should I move them to main.h, so they can sit next to ProgramStart? Seems like a nice place since they'd all be using executionEnvironment.

The ERRMSG argument could be a nullable pointer argument to ArgumentValue.

Why a nullable pointer and not a descriptor? I'm also wondering this about \p value, should that also be passed as a pointer + length rather than a descriptor?

[klausler]

In D108688#2966694, @rovka wrote:

In D108688#2965273, @klausler wrote:

environment.h is not a header for APIs.

Ok, should I move them to main.h, so they can sit next to ProgramStart? Seems like a nice place since they'd all be using executionEnvironment.

Fine.

The ERRMSG argument could be a nullable pointer argument to ArgumentValue.

Why a nullable pointer and not a descriptor? I'm also wondering this about \p value, should that also be passed as a pointer + length rather than a descriptor?

I mean the argument can be a pointer (not reference) to a descriptor, and the pointer can be null if there is no ERRMSG=.

[rovka]

In D108688#2967602, @klausler wrote:

In D108688#2966694, @rovka wrote:

In D108688#2965273, @klausler wrote:

The ERRMSG argument could be a nullable pointer argument to ArgumentValue.

Why a nullable pointer and not a descriptor? I'm also wondering this about \p value, should that also be passed as a pointer + length rather than a descriptor?

I mean the argument can be a pointer (not reference) to a descriptor, and the pointer can be null if there is no ERRMSG=.

Right, I got a bit confused there, thanks for clarifying :) I'll make both of them nullable, since it's clearer and simpler than having to check if the descriptor is allocated.

[jeanPerier]

flang/runtime/environment.h

61 ↗

(On Diff #368568)

Could you make all the Descriptor& and Descriptor* const ? The runtime will modify the value described by the descriptors, but it should not modify the descriptors themselves.

In lowering, const Descriptor& and Descriptor& do not end-up being handled the same in FIR (because FIR cares if descriptors may be modified in meaningful way by a function), so it's important to make them const when they are not intended to be modified by the runtime.

[rovka]

Addressed review comments:

• Moved everything to command.h.
• s/Descriptor &/const Descriptor */
• Removed ArgumentValueVerbose entry point.

flang/runtime/command.h

 //===-- runtime/command.h ---------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef FORTRAN_RUNTIME_COMMAND_H_
 #define FORTRAN_RUNTIME_COMMAND_H_
 
 #include "cpp-type.h"
 #include "entry-names.h"
 
 namespace Fortran::runtime {
+class Descriptor;
+
 extern "C" {
 // 16.9.51 COMMAND_ARGUMENT_COUNT
 //
 // Lowering may need to cast the result to match the precision of the default
 // integer kind.
 CppTypeFor<TypeCategory::Integer, 4> RTNAME(ArgumentCount)();
+
+// 16.9.83 GET_COMMAND_ARGUMENT
+// We're breaking up the interface into several different functions, since most
+// of the parameters are optional.
+
+// Try to get the value of the n'th argument.
+// Returns a STATUS as described in the standard.
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(ArgumentValue)(
+    CppTypeFor<TypeCategory::Integer, 4> n, const Descriptor *value,
+    const Descriptor *errmsg);
+
+// Try to get the significant length of the n'th argument.
+// Returns 0 if it doesn't manage.
+CppTypeFor<TypeCategory::Integer, 4> RTNAME(ArgumentLength)(
+    CppTypeFor<TypeCategory::Integer, 4> n);
 }
 } // namespace Fortran::runtime
 
 #endif // FORTRAN_RUNTIME_COMMAND_H_