[flang] Add runtime interface for GET_COMMAND

[rovka]

Summary

Use a single entry point with many optional parameters.

[klausler]

The entry point name should reflect the name of the intrinsic procedure more closely.

We will probably have to rethink the interface soon so that the runtime can cope better with intrinsic procedure arguments that are optional and that can't be known to be present or absent until execution.

[rovka]

Like this?

[jeanPerier]

flang/include/flang/Runtime/command.h

31

Passing length as a simple pointer is tempting, but I think it will be problematic because the actual Fortran entity for the length is not guaranteed to be a INTEGER(8). It is only required that it must have a decimal exponent range of at least four.

So if we blindly cast and pass the length in lowering, we may have troubles. And dealing with maybe allocating an INTEGER(8) temp is not easier than the previous interface.

So, I think this either has to be a const Descriptor *length, or lowering has to get more clever and be able to deal with dynamically optional argument with your previous interface.

I tend to think const Descriptor *length is the easiest solution, and since this is not a computational intrinsic, I am not sure the descriptor overhead is a big deal.

@klausler , do you agree ?

[klausler]

A descriptor would work, yes,. Another approach, which is used in the I/O runtime API for some integer results, is a void* pointer and a KIND code.

[rovka]

Ok, I updated it to use a descriptor instead, for brevity mostly.

flang/include/flang/Runtime/command.h

 
 extern "C" {
 // 16.9.51 COMMAND_ARGUMENT_COUNT
 //
 // Lowering may need to cast the result to match the precision of the default
 // integer kind.
 std::int32_t RTNAME(ArgumentCount)();
 
+// 16.9.82 GET_COMMAND
+// Try to get the value of the whole command. All of the parameters are
+// optional.
+// Return a STATUS as described in the standard.
+std::int32_t RTNAME(GetCommand)(const Descriptor *command = nullptr,
+    const Descriptor *length = nullptr, const Descriptor *errmsg = nullptr);
+
 // 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.
 std::int32_t RTNAME(ArgumentValue)(
     std::int32_t n, const Descriptor *value, const Descriptor *errmsg);