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Fix 8.4 + CUDA 11.4 build (#789)

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Work around a likely GCC 8.x issue with fold expressions
and generic lambdas.

Only use the work-around when the host compiler is GCC 8.x.
This avoids any concerns about the work-around possibly
hindering inlining for a critical CuTe function (product).

Users can experiment with the work-around for other compilers
or compiler versions by defining the following macro.

CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND

Fixes https://github.com/NVIDIA/cutlass/issues/788

Co-authored-by: Mark Hoemmen <mhoemmen@nvidia.com>
This commit is contained in:
Mark Hoemmen 2023-01-27 07:18:59 -07:00 committed by GitHub
parent 277bd6e537
commit add4ba622f
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1 changed files with 57 additions and 0 deletions
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57
include/cute/int_tuple.hpp
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@ -219,13 +219,70 @@ product(IntTuple const& a)
CUTE_GCC_UNREACHABLE;
}
// Work-around for some compiler versions (e.g., GCC 8.x)
// incorrectly not being able to compile certain
// legal C++ fold expressions inside generic lambdas.
// Issue is known to exist in GCC 8.4 and GCC 8.5.
// Work-around should be valid portable CUDA C++.
#if ! defined(CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND)
# if defined(__GNUC__) && __GNUC__ == 8
# define CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND 1
# endif
#endif
#if defined(CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND)
namespace impl {
template<int B, int E>
struct SubrangeProductImpl {
// GCC 8.4 accepts the fold expression here. If that doesn't work,
// the other branch (recursive operator()) is known to build
// with GCC 8.4 as well. The code does not enable recursion by default,
// as fold expressions might be easier for compilers to optimize.
#if 1
template<class ... Args>
CUTE_HOST_DEVICE constexpr auto
operator()(Args const&... args) const
{
return (Int<1>{} * ... * product(args));
}
#else
CUTE_HOST_DEVICE constexpr Int<1>
operator()() const
{
return Int<1>{};
}
template<class Head, class ... Tail>
CUTE_HOST_DEVICE constexpr auto
operator()(Head const& head, Tail const&... tail) const
{
return (*this)(tail...) * product<Head>(head);
}
#endif // 1
};
} // namespace impl
#endif // defined(CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND)
// Product of a subrange
template <int B, int E, class Tuple>
CUTE_HOST_DEVICE constexpr
auto
product(Tuple const& a)
{
// Work around some compiler versions that do not accept
// the generic lambda in the else branch, by replacing
// the lambda with a function object. The work-around
// is legal C++17, but the original code might be easier
// for non-broken compilers to optimize, so it remains.
#if defined(CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND)
impl::SubrangeProductImpl<B, E> function_object;
return detail::apply(a, function_object, make_range<B, E>{});
#else
return detail::apply(a, [](auto const&... v){ return (Int<1>{} * ... * product(v)); }, make_range<B,E>{});
#endif // defined(CUTE_FOLD_GENERIC_LAMBDA_WORKAROUND)
}
template <class Tuple>