C++ interface templates appear to be broken #1904
Comments
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Yeah it is known that references aren't handled properly in the new interface, help definitely welcome! And yeah tentaitlvely c++17, though obviously earlier support would be nice if possible |
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Adding a MFE which used to work in the original PR for the C++ interface https://fwd.gymni.ch/nsKPWF |
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@jandrej with #1914 your code compiles with the following minor changes: 62,64c62,63
< return std::tuple<enzyme::Duplicated<decltype(std::get<Is>(args))>...>{
< { std::get<Is>(args), std::get<Is>(shadow_args) }...
< };
---
> return std::tuple_cat(std::make_tuple(
> enzyme::Duplicated<std::remove_cv_t<std::remove_reference_t<decltype(std::get<Is>(args))>>*> {&std::get<Is>(args), &std::get<Is>(shadow_args)})...);
87c86
< enzyme::autodiff<enzyme::Forward>
---
> enzyme::autodiff<enzyme::Forward, enzyme::DuplicatedNoNeed<kf_return_t>>
106,110c105
< std::get<0>(kernel_args) = 3;
< std::get<0>(kernel_shadow_args) = 1;
<
< const auto res = fwddiff_apply_enzyme(func, kernel_args, kernel_shadow_args);
< std::cout << res << " == 6\n";
---
> fwddiff_apply_enzyme(func, kernel_args, kernel_shadow_args);(I've replaced It still doesn't work as intended (prints #include <enzyme/enzyme>
#include <iostream>
double f(const double& x) { return x * x; }
int main() {
double x = 3, dx = 0;
enzyme::autodiff<enzyme::Reverse>(
f, enzyme::Duplicated<const double&>{ x, dx }
);
std::cout << x << ' ' << dx << '\n';
return 0;
}will compile and work meanwhile this: #include <enzyme/enzyme>
#include <iostream>
double f(const double& x) { return x * x; }
int main() {
double x = 3, dx = 0;
enzyme::autodiff<enzyme::Reverse>(
&f, enzyme::Duplicated<const double&>{ x, dx }
);
std::cout << x << ' ' << dx << '\n';
return 0;
}will not: (nevermind the line numbers, I'm testing everything in a single |
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@GregTheMadMonk the issue is that we need to ensure that all the reference passes do not end up creating a copy and thus the autodiff/fwddiff call gets the pointer to the actual reference provided. Re function pointers, they are supported, but when passed directly. (like the top) |
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@wsmoses Sorry, I'm not sure I quite follow what you're saying... Do you mean that we need to ensure that the pointer Then there is also the issue that I've written about in the PR comments - but I see you've already read and replied to it :) And I also realize (now) why function pointers can't really be processed (since a function pointer could point to any function really and there is no guarantee it was processed by Enzyme). It seems that the best self-critique arrives after the code has been submitted... It's getting quite late, I won't be replying for a while |
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So we can find out what's happening by looking at the generated LLVM. If there's a copy somewhere we'll see a different allocation passed to the underlying It would be nice to do a check at the outermost c++ api level (though we have some internal shenanigans to handle a slightly wider scope). |
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@GregTheMadMonk did you check the output values? I only get zeros from the fwddiff in your branch. |
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Seemingly resolved. |
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Thank you! Sorry for being very inconsistent with GH activity |
Hello! Playing with C++ interface trying to get it to work and this simple program:
doesn't compile with the following errors:
It seems that the interface
std::stuff with an internalenzyme::tupleUnless I terribly misunderstand something, this is an error.
If it is, I think I'm going to try and fix it
edit: btw, what version of C++ should I use if editing the headers? C++17, or do you target lower versions too?
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