peixin added inline comments.
================
Comment at: flang/test/Driver/emit-mlir.f90:16
! CHECK-NEXT: }
+! CHECK-NEXT: fir.global @_QQEnvironmentDefaults constant :
!fir.ref<tuple<i[[int_size:.*]], !fir.ref<!fir.array<0xtuple<!fir.ref<i8>,
!fir.ref<i8>>>>>> {
+! CHECK-NEXT: %[[VAL_0:.*]] = fir.zero_bits !fir.ref<tuple<i[[int_size]],
!fir.ref<!fir.array<0xtuple<!fir.ref<i8>, !fir.ref<i8>>>>>>
----------------
jpenix-quic wrote:
> peixin wrote:
> > jpenix-quic wrote:
> > > peixin wrote:
> > > > jpenix-quic wrote:
> > > > > peixin wrote:
> > > > > > Is it possible not to generated this global variable if `fconvert=`
> > > > > > is not specified?
> > > > > I'm not entirely sure--the issue I was running into was how to handle
> > > > > this in Fortran_main.c in a way which worked for all of
> > > > > GCC/Clang/Visual Studio (and maybe others?). I was originally
> > > > > thinking of doing this by using a weak definition of
> > > > > _QQEnvironmentDefaults set to nullptr so fconvert, etc. could
> > > > > override this definition without explicitly generating the fallback
> > > > > case. For GCC/clang, I think I could use __attribute__((weak)), but I
> > > > > wasn't sure how to handle this if someone tried to build with Visual
> > > > > Studio (or maybe another toolchain). I saw a few workarounds (ex:
> > > > > https://devblogs.microsoft.com/oldnewthing/20200731-00/?p=104024) but
> > > > > I shied away from this since it seems to be an undocumented feature
> > > > > (and presumably only helps with Visual Studio).
> > > > >
> > > > > Do you know of a better or more general way I could do this? (Or, is
> > > > > there non-weak symbol approach that might be better that I'm missing?)
> > > > How about generate one runtime function with the argument of
> > > > `EnvironmentDefaultList`? This will avoid this and using one extern
> > > > variable?
> > > >
> > > > If users use one variable with bind C name `_QQEnvironmentDefaults` in
> > > > fortran or one variable with name `_QQEnvironmentDefaults` in C, it is
> > > > risky. Would using the runtime function and static variable with the
> > > > type `EnvironmentDefaultList` in runtime be safer?
> > > Agreed that there are potential risks with the current approach
> > > (although, are the `_Q*` names considered reserved?). Unfortunately, I
> > > think generating a call to set the environment defaults requires somewhat
> > > significant changes to the runtime. The runtime reads environment
> > > variables during initialization in `ExecutionEnvironment::Configure`
> > > which is ultimately called from the "hardcoded" `Fortran_main.c` and I
> > > need to set the defaults before this happens. So, I believe I'd either
> > > have to move the initialization to `_QQmain` or make it so that `main`
> > > isn't hardcoded so that I could insert the appropriate runtime function.
> > >
> > > @klausler I think I asked you about this when I was first trying to
> > > figure out how to implement the environment defaults and you suggested I
> > > try the extern approach--please let me know if you have
> > > thoughts/suggestions around this!
> > This is what @klausler suggested:
> > ```
> > Instead of adding new custom APIs that let command-line options control
> > behavior in a way that is redundant with the runtime environment, I suggest
> > that you try a more general runtime library API by which the main program
> > can specify a default environment variable setting, or a set of them. Then
> > turn the command-line options into the equivalent environment settings and
> > pass them as default settings that could be overridden by the actual
> > environment.
> > ```
> > If I understand correctly, what I am suggesting match his comments. The
> > "main program" he means should be fortran main program, not the
> > `RTNAME(ProgramStart`. In your initial patch, you add the runtime specified
> > for "convert option". I think @klausler suggest you making the runtime
> > argument more general used for a set of runtime environment variable
> > settings, not restricted to "convert option". And that is what you already
> > added -- `EnvironmentDefaultList`. So, combining this patch and your
> > initial patch will be the solution. Hope I understand it correctly.
> The issue I hit with the suggested approach is that in order to use the
> pre-existing runtime environment variable handling to set the internal state
> I need to set the environment variable defaults before the environment
> variables are read by the runtime.
>
> I might be misunderstanding/missing something, but given that the environment
> variables are read as part of `RTNAME(ProgramStart)` in `main` and the
> earliest I can place the call if I am generating it is `_QQmain`, I think
> that leaves three options: 1. don't hardcode `main` so that I can place the
> call early enough 2. delay or rerun the code [[
> https://github.com/llvm/llvm-project/blob/c619d4f840dcba54751ff8c5aaafce0f173a4ad5/flang/runtime/environment.cpp#L50-L90
> | here ]] that is responsible for initializing the runtime state so that it
> is called as part of `_QQmain` so I can insert my runtime function before it
> or 3. hardcode something like the `_QQEnvironmentDefaults` into
> Fortran_main.c so that the environment defaults are available early enough.
> Option 2 seems less than ideal to me, option 1 seems ideal but requires
> generating `main`, so option 3 is what I ended up going with. If options 1 or
> 2 would be preferable to what is currently implemented (or if there is
> another possibility I'm missing!) I'd be happy to switch and try to implement
> them.
>
What do other reviewers think? @klausler @awarzynski @kiranchandramohan
@clementval @jeanPerier
The current approach has two drawbacks:
1. Add one extern variable `_QQEnvironmentDefaults` in runtime.
2. Generate the variable during lowering even if there is no `-fconvert` option.
Can we accept this?
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D130513/new/
https://reviews.llvm.org/D130513
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