awarzynski added inline comments.
================
Comment at:
flang/include/flang/Optimizer/Builder/Runtime/EnvironmentDefaults.h:7
+//
+//===----------------------------------------------------------------------===//
+
----------------
Could you document what these are? And what are they used for?
================
Comment at: flang/lib/Frontend/CompilerInvocation.cpp:403-413
+ if (const auto *arg =
+ args.getLastArg(clang::driver::options::OPT_fconvert_EQ)) {
+ auto parseConvertArg = [](const char *s) {
+ return llvm::StringSwitch<std::optional<const char *>>(s)
+ .Case("unknown", "UNKNOWN")
+ .Case("native", "NATIVE")
+ .Case("little-endian", "LITTLE_ENDIAN")
----------------
I'm OK with a lambda here, just pointing our that in other cases we added small
hooks, e.g. `getOptimizationLevel`. I personally prefer hooks as this means
that methods like `parseFrontendArgs` can be a bit shorter. But this is a very
weak preference!
================
Comment at: flang/test/Driver/convert.f90:1
+! Ensure argument -fconvert=<value> works as expected.
+
----------------
Could you be more specific? IIUC, this is more about making sure that the
option parser works correctly and reports invalid usage of `-fconvert` as an
error, right?
================
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>>>>>>
----------------
peixin wrote:
> 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?
Based on the analysis by @jpenix-quic, this is the path of least resistance and
SGTM. It can always be refactored/improved in the future if need be. It would
be helpful if this was documented somewhere. But I'm not sure whether there's
a good landing space for this ATM.
================
Comment at: flang/test/Lower/environment-defaults.f90:1
+! RUN: bbc -emit-fir -o - %s | FileCheck %s
+
----------------
Can you test with `flang-new` as well?
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D130513/new/
https://reviews.llvm.org/D130513
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