Now that the requirements and implementation of asynchronous I/O are
better understood, adjust their I/O runtime APIs. In particular:
1) Remove the BeginAsynchronousOutput/Input APIs; they're not needed,
since any data transfer statement might have ASYNCHRONOUS= and
(if ASYNCHRONOUS='YES') ID= control list specifiers that need to
at least be checked.
2) Add implementations for BeginWait(All) to check for the error
case of a bad unit number and nonzero ID=.
3) Rearrange and comment SetAsynchronous so that it's clear that
it can be called for READ/WRITE as well as for OPEN.
The implementation remains completely synchronous, but should be conforming.
Where opportunities make sense for true asynchronous implementations of
some big block transfers without SIZE= in the future, we'll need to add
a GetAsynchronousId API to capture ID= on a READ or WRITE; add sourceFile
and sourceLine arguments to BeginWait(All) for good error reporting;
track pending operations in unit.h; and add code to force synchronization
to non-asynchronous I/O operations.
Lowering should call SetAsynchronous when ASYNCHRONOUS= appears as
a control list specifier. It should also set ID=x variables to 0
until such time as we support asynchronous operations, if ever.
This patch only removes the removed APIs from lowering.
Differential Revision: https://reviews.llvm.org/D126143
deb62f5ad6