instance: only polymorphize upvar substs

This commit restricts the substitution polymorphization added in #75255
to only apply to the tupled upvar substitution, rather than all
substitutions, fixing a bunch of regressions when polymorphization is
enabled.

Signed-off-by: David Wood <david@davidtw.co>

5 files changed, 33 insertions, 88 deletions

diff --git a/src/librustc_middle/ty/flags.rs b/src/librustc_middle/ty/flags.rs
index 81f7474962c..27f50c240db 100644
--- a/src/librustc_middle/ty/flags.rs
+++ b/src/librustc_middle/ty/flags.rs
@@ -85,8 +85,6 @@ impl FlagComputation {
             }
 
             &ty::Generator(_, ref substs, _) => {
-                self.add_flags(TypeFlags::MAY_POLYMORPHIZE);
-
                 let substs = substs.as_generator();
                 let should_remove_further_specializable =
                     !self.flags.contains(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
@@ -109,8 +107,6 @@ impl FlagComputation {
             }
 
             &ty::Closure(_, substs) => {
-                self.add_flags(TypeFlags::MAY_POLYMORPHIZE);
-
                 let substs = substs.as_closure();
                 let should_remove_further_specializable =
                     !self.flags.contains(TypeFlags::STILL_FURTHER_SPECIALIZABLE);
@@ -196,8 +192,6 @@ impl FlagComputation {
             }
 
             &ty::FnDef(_, substs) => {
-                self.add_flags(TypeFlags::MAY_POLYMORPHIZE);
-
                 self.add_substs(substs);
             }
 
diff --git a/src/librustc_middle/ty/fold.rs b/src/librustc_middle/ty/fold.rs
index 87434f3f267..492f8ce9ef1 100644
--- a/src/librustc_middle/ty/fold.rs
+++ b/src/librustc_middle/ty/fold.rs
@@ -150,12 +150,6 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
         self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
     }
 
-    /// Does this value contain closures, generators or functions such that it may require
-    /// polymorphization?
-    fn may_polymorphize(&self) -> bool {
-        self.has_type_flags(TypeFlags::MAY_POLYMORPHIZE)
-    }
-
     /// A visitor that does not recurse into types, works like `fn walk_shallow` in `Ty`.
     fn visit_tys_shallow(&self, visit: impl FnMut(Ty<'tcx>) -> bool) -> bool {
         pub struct Visitor<F>(F);
diff --git a/src/librustc_middle/ty/instance.rs b/src/librustc_middle/ty/instance.rs
index cf876db26bc..2def000da64 100644
--- a/src/librustc_middle/ty/instance.rs
+++ b/src/librustc_middle/ty/instance.rs
@@ -492,6 +492,20 @@ fn polymorphize<'tcx>(
     let unused = tcx.unused_generic_params(def_id);
     debug!("polymorphize: unused={:?}", unused);
 
+    // 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>,
     };
@@ -512,14 +526,6 @@ fn polymorphize<'tcx>(
                         self.tcx.mk_closure(def_id, polymorphized_substs)
                     }
                 }
-                ty::FnDef(def_id, substs) => {
-                    let polymorphized_substs = polymorphize(self.tcx, def_id, substs);
-                    if substs == polymorphized_substs {
-                        ty
-                    } else {
-                        self.tcx.mk_fn_def(def_id, polymorphized_substs)
-                    }
-                }
                 ty::Generator(def_id, substs, movability) => {
                     let polymorphized_substs = polymorphize(self.tcx, def_id, substs);
                     if substs == polymorphized_substs {
@@ -537,24 +543,31 @@ fn polymorphize<'tcx>(
         let is_unused = unused.contains(param.index).unwrap_or(false);
         debug!("polymorphize: param={:?} is_unused={:?}", param, is_unused);
         match param.kind {
-            // If parameter is a const or type parameter..
+            // 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..
             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),
 
-            // If the parameter does not contain any closures or generators, then use the
-            // substitution directly.
-            _ if !substs.may_polymorphize() => substs[param.index as usize],
-
-            // Otherwise, use the substitution after polymorphizing.
-            _ => {
-                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)
-            }
+            // Otherwise, use the parameter as before.
+            _ => substs[param.index as usize],
         }
     })
 }
diff --git a/src/librustc_middle/ty/mod.rs b/src/librustc_middle/ty/mod.rs
index 0102225b9b5..6798addb8aa 100644
--- a/src/librustc_middle/ty/mod.rs
+++ b/src/librustc_middle/ty/mod.rs
@@ -575,10 +575,6 @@ bitflags! {
         /// Does this value have parameters/placeholders/inference variables which could be
         /// replaced later, in a way that would change the results of `impl` specialization?
         const STILL_FURTHER_SPECIALIZABLE = 1 << 17;
-
-        /// Does this value contain closures, generators or functions such that it may require
-        /// polymorphization?
-        const MAY_POLYMORPHIZE = 1 << 18;
     }
 }
 
diff --git a/src/test/codegen-units/polymorphization/pr-75255.rs b/src/test/codegen-units/polymorphization/pr-75255.rs
deleted file mode 100644
index af47b440640..00000000000
--- a/src/test/codegen-units/polymorphization/pr-75255.rs
+++ /dev/null
@@ -1,52 +0,0 @@
-// 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` and `iter::repeat` are generated.
-
-fn unused<T>() -> u64 {
-    42
-}
-
-fn foo<T>() {
-    let x = [1, 2, 3, std::mem::size_of::<T>()];
-    x.iter().map(|_| ());
-}
-
-//~ 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]
-
-fn bar<T>() {
-    std::iter::repeat(unused::<T>);
-}
-
-//~ MONO_ITEM fn core::iter[0]::sources[0]::repeat[0]<fn() -> u64> @@ pr_75255-cgu.1[Internal]
-
-pub fn dispatch() {
-    foo::<String>();
-    foo::<Vec<String>>();
-
-    bar::<String>();
-    bar::<Vec<String>>();
-}
-
-// 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]
-//~ MONO_ITEM fn pr_75255::bar[0]<alloc::string[0]::String[0]> @@ pr_75255-cgu.1[Internal]
-//~ MONO_ITEM fn pr_75255::bar[0]<alloc::vec[0]::Vec[0]<alloc::string[0]::String[0]>> @@ pr_75255-cgu.1[Internal]