Auto merge of #69749 - davidtwco:issue-46477-polymorphization, r=eddyb

Polymorphization

This PR implements an analysis to detect when functions could remain polymorphic during code generation.

Fixes #46477

r? @eddyb
cc @rust-lang/wg-mir-opt @nikomatsakis @pnkfelix

Author: bors

src/librustc_codegen_llvm/callee.rs

@@ -13,7 +13,7 @@ use log::debug;
 use rustc_codegen_ssa::traits::*;
 
 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
-use rustc_middle::ty::{Instance, TypeFoldable};
+use rustc_middle::ty::{self, Instance, TypeFoldable};
 
 /// Codegens a reference to a fn/method item, monomorphizing and
 /// inlining as it goes.
@@ -29,14 +29,18 @@ pub fn get_fn(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) -> &'ll Value
 
     assert!(!instance.substs.needs_infer());
     assert!(!instance.substs.has_escaping_bound_vars());
-    assert!(!instance.substs.has_param_types_or_consts());
 
     if let Some(&llfn) = cx.instances.borrow().get(&instance) {
         return llfn;
     }
 
     let sym = tcx.symbol_name(instance).name;
-    debug!("get_fn({:?}: {:?}) => {}", instance, instance.monomorphic_ty(cx.tcx()), sym);
+    debug!(
+        "get_fn({:?}: {:?}) => {}",
+        instance,
+        instance.ty(cx.tcx(), ty::ParamEnv::reveal_all()),
+        sym
+    );
 
     let fn_abi = FnAbi::of_instance(cx, instance, &[]);
 

src/librustc_codegen_llvm/consts.rs

@@ -203,7 +203,7 @@ impl CodegenCx<'ll, 'tcx> {
             def_id
         );
 
-        let ty = instance.monomorphic_ty(self.tcx);
+        let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
         let sym = self.tcx.symbol_name(instance).name;
 
         debug!("get_static: sym={} instance={:?}", sym, instance);
@@ -361,7 +361,7 @@ impl StaticMethods for CodegenCx<'ll, 'tcx> {
             };
 
             let instance = Instance::mono(self.tcx, def_id);
-            let ty = instance.monomorphic_ty(self.tcx);
+            let ty = instance.ty(self.tcx, ty::ParamEnv::reveal_all());
             let llty = self.layout_of(ty).llvm_type(self);
             let g = if val_llty == llty {
                 g