remove polymorphization

src/backend/monomorph.md

@@ -79,77 +79,3 @@ For more details about the partitioner read the module level [documentation].
 [mono]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_monomorphize/partitioning/fn.collect_and_partition_mono_items.html
 [codegen1]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/base/fn.codegen_crate.html
 [documentation]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_monomorphize/partitioning/index.html
-
-## Polymorphization
-
-As mentioned above, monomorphization produces fast code, but it comes at the
-cost of compile time and binary size. [MIR optimizations][miropt] can help a
-bit with this.
-
-In addition to MIR optimizations, rustc attempts to determine when fewer
-copies of functions are necessary and avoid making those copies - known
-as "polymorphization". When a function-like item is found during
-monomorphization collection, the
-[`rustc_mir_monomorphize::polymorphize::unused_generic_params`][polymorph]
-query is invoked, which traverses the MIR of the item to determine on which
-generic parameters the item might not need duplicated.
-
-Currently, polymorphization only looks for unused generic parameters. These
-are relatively rare in functions, but closures inherit the generic
-parameters of their parent function and it is common for closures to not
-use those inherited parameters. Without polymorphization, a copy of these
-closures would be created for each copy of the parent function. By
-creating fewer copies, less LLVM IR is generated; therefore less needs to be processed.
-
-`unused_generic_params` returns a `FiniteBitSet<u64>` where a bit is set if
-the generic parameter of the corresponding index is unused. Any parameters
-after the first sixty-four are considered used.
-
-The results of polymorphization analysis are used in the
-[`Instance::polymorphize`][inst_polymorph] function to replace the
-[`Instance`][inst]'s substitutions for the unused generic parameters with their
-identity substitutions.
-
-Consider the example below:
-
-```rust
-fn foo<A, B>() {
-    let x: Option<B> = None;
-}
-
-fn main() {
-    foo::<u16, u32>();
-    foo::<u64, u32>();
-}
-```
-
-During monomorphization collection, `foo` will be collected with the
-substitutions `[u16, u32]` and `[u64, u32]` (from its invocations in `main`).
-`foo` has the identity substitutions `[A, B]` (or
-`[ty::Param(0), ty::Param(1)]`).
-
-Polymorphization will identify `A` as being unused and it will be replaced in
-the substitutions with the identity parameter before being added to the set
-of collected items - thereby reducing the copies from two (`[u16, u32]` and
-`[u64, u32]`) to one (`[A, u32]`).
-
-`unused_generic_params` will also be invoked during code generation when the
-symbol name for `foo` is being computed for use in the callsites of `foo`
-(which have the regular substitutions present, otherwise there would be a
-symbol mismatch between the caller and the function).
-
-As a result of polymorphization, items collected during monomorphization
-cannot be assumed to be monomorphic.
-
-It is intended that polymorphization be extended to more advanced cases,
-such as where only the size/alignment of a generic parameter are required.
-
-More details on polymorphization are available in the
-[master's thesis][thesis] associated with polymorphization's initial
-implementation.
-
-[miropt]: ../mir/optimizations.md
-[polymorph]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_monomorphize/polymorphize/fn.unused_generic_params.html
-[inst]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/instance/struct.Instance.html
-[inst_polymorph]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/instance/struct.Instance.html#method.polymorphize
-[thesis]: https://davidtw.co/media/masters_dissertation.pdf