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instance: always polymorphize substs

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By always polymorphizing substitutions, functions which take closures as
arguments (e.g. `impl Fn()`) can have fewer mono items when some of the
argument closures can be polymorphized.

Signed-off-by: David Wood <david@davidtw.co>
This commit is contained in:
David Wood 2020-08-07 17:11:16 +01:00
parent d9decede35
commit 0d9924a87b
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GPG Key ID: 2592E76C87381FD9
2 changed files with 45 additions and 38 deletions
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46
src/librustc_middle/ty/instance.rs
View File

@ -492,25 +492,6 @@ fn polymorphize<'tcx>(
let unused = tcx.unused_generic_params(def_id);
debug!("polymorphize: unused={:?}", unused);
if unused.is_empty() {
// Exit early if every parameter was used.
return substs;
}
// If this is a closure or generator then we need to handle the case where another closure
// from the function is captured as an upvar and hasn't been polymorphized. In this case,
// the unpolymorphized upvar closure would result in a polymorphized closure producing
// multiple mono items (and eventually symbol clashes).
let upvars_ty = if tcx.is_closure(def_id) {
Some(substs.as_closure().tupled_upvars_ty())
} else if tcx.type_of(def_id).is_generator() {
Some(substs.as_generator().tupled_upvars_ty())
} else {
None
};
let has_upvars = upvars_ty.map(|ty| ty.tuple_fields().count() > 0).unwrap_or(false);
debug!("polymorphize: upvars_ty={:?} has_upvars={:?}", upvars_ty, has_upvars);
struct PolymorphizationFolder<'tcx> {
tcx: TyCtxt<'tcx>,
};
@ -540,31 +521,20 @@ fn polymorphize<'tcx>(
let is_unused = unused.contains(param.index).unwrap_or(false);
debug!("polymorphize: param={:?} is_unused={:?}", param, is_unused);
match param.kind {
// Upvar case: If parameter is a type parameter..
ty::GenericParamDefKind::Type { .. } if
// ..and has upvars..
has_upvars &&
// ..and this param has the same type as the tupled upvars..
upvars_ty == Some(substs[param.index as usize].expect_ty()) => {
// ..then double-check that polymorphization marked it used..
debug_assert!(!is_unused);
// ..and polymorphize any closures/generators captured as upvars.
let upvars_ty = upvars_ty.unwrap();
let polymorphized_upvars_ty = upvars_ty.fold_with(
&mut PolymorphizationFolder { tcx });
debug!("polymorphize: polymorphized_upvars_ty={:?}", polymorphized_upvars_ty);
ty::GenericArg::from(polymorphized_upvars_ty)
},
// Simple case: If parameter is a const or type parameter..
// If parameter is a const or type parameter..
ty::GenericParamDefKind::Const | ty::GenericParamDefKind::Type { .. } if
// ..and is within range and unused..
unused.contains(param.index).unwrap_or(false) =>
// ..then use the identity for this parameter.
tcx.mk_param_from_def(param),
// Otherwise, use the parameter as before.
_ => substs[param.index as usize],
// Otherwise, use the parameter as before (polymorphizing any closures or generators).
_ => {
let arg = substs[param.index as usize];
let polymorphized_arg = arg.fold_with(&mut PolymorphizationFolder { tcx });
debug!("polymorphize: arg={:?} polymorphized_arg={:?}", arg, polymorphized_arg);
ty::GenericArg::from(polymorphized_arg)
}
}
})
}

37
src/test/codegen-units/polymorphization/pr-75255.rs Normal file
View File

@ -0,0 +1,37 @@
// compile-flags:-Zpolymorphize=on -Zprint-mono-items=lazy -Copt-level=1
// ignore-tidy-linelength
#![crate_type = "rlib"]
// Test that only one copy of `Iter::map` is generated.
fn foo<T>() {
let x = [1, 2, 3, std::mem::size_of::<T>()];
x.iter().map(|_| ());
}
pub fn dispatch() {
foo::<String>();
foo::<Vec<String>>();
}
//~ MONO_ITEM fn core::iter[0]::adapters[0]::{{impl}}[29]::new[0]<core::slice[0]::Iter[0]<usize>, pr_75255::foo[0]::{{closure}}[0]<T>> @@ pr_75255-cgu.0[External]
//~ MONO_ITEM fn core::iter[0]::traits[0]::iterator[0]::Iterator[0]::map[0]<core::slice[0]::Iter[0]<usize>, (), pr_75255::foo[0]::{{closure}}[0]<T>> @@ pr_75255-cgu.1[Internal]
// These are all the items that aren't relevant to the test.
//~ MONO_ITEM fn core::mem[0]::size_of[0]<alloc::string[0]::String[0]> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::mem[0]::size_of[0]<alloc::vec[0]::Vec[0]<alloc::string[0]::String[0]>> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::mem[0]::size_of[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::const_ptr[0]::{{impl}}[0]::add[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::const_ptr[0]::{{impl}}[0]::is_null[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::const_ptr[0]::{{impl}}[0]::offset[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::const_ptr[0]::{{impl}}[0]::wrapping_add[0]<u8> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::const_ptr[0]::{{impl}}[0]::wrapping_offset[0]<u8> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::non_null[0]::{{impl}}[3]::new_unchecked[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::ptr[0]::null[0]<u8> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::slice[0]::{{impl}}[0]::as_ptr[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::slice[0]::{{impl}}[0]::iter[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn core::slice[0]::{{impl}}[0]::len[0]<usize> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn pr_75255::dispatch[0] @@ pr_75255-cgu.1[External]
//~ MONO_ITEM fn pr_75255::foo[0]<alloc::string[0]::String[0]> @@ pr_75255-cgu.1[Internal]
//~ MONO_ITEM fn pr_75255::foo[0]<alloc::vec[0]::Vec[0]<alloc::string[0]::String[0]>> @@ pr_75255-cgu.1[Internal]