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

5 files changed, 20 insertions, 17 deletions

diff --git a/src/librustc_codegen_ssa/debuginfo/type_names.rs b/src/librustc_codegen_ssa/debuginfo/type_names.rs
index 20d440433cb..fb8f5a62989 100644
--- a/src/librustc_codegen_ssa/debuginfo/type_names.rs
+++ b/src/librustc_codegen_ssa/debuginfo/type_names.rs
@@ -205,14 +205,17 @@ pub fn push_debuginfo_type_name<'tcx>(
                 tcx.def_key(def_id).disambiguated_data.disambiguator
             ));
         }
+        // Type parameters from polymorphized functions.
+        ty::Param(_) => {
+            output.push_str(&format!("{:?}", t));
+        }
         ty::Error(_)
         | ty::Infer(_)
         | ty::Placeholder(..)
         | ty::Projection(..)
         | ty::Bound(..)
         | ty::Opaque(..)
-        | ty::GeneratorWitness(..)
-        | ty::Param(_) => {
+        | ty::GeneratorWitness(..) => {
             bug!(
                 "debuginfo: Trying to create type name for \
                   unexpected type: {:?}",
diff --git a/src/librustc_codegen_ssa/meth.rs b/src/librustc_codegen_ssa/meth.rs
index 199dd8c7df4..cfa01280e5a 100644
--- a/src/librustc_codegen_ssa/meth.rs
+++ b/src/librustc_codegen_ssa/meth.rs
@@ -94,7 +94,8 @@ pub fn get_vtable<'tcx, Cx: CodegenMethods<'tcx>>(
                     def_id,
                     substs,
                 )
-                .unwrap(),
+                .unwrap()
+                .polymorphize(cx.tcx()),
             )
         })
     });
diff --git a/src/librustc_codegen_ssa/mir/analyze.rs b/src/librustc_codegen_ssa/mir/analyze.rs
index db935c2b3e2..2e386c1e594 100644
--- a/src/librustc_codegen_ssa/mir/analyze.rs
+++ b/src/librustc_codegen_ssa/mir/analyze.rs
@@ -124,8 +124,7 @@ impl<Bx: BuilderMethods<'a, 'tcx>> LocalAnalyzer<'mir, 'a, 'tcx, Bx> {
                 let base_ty = self.fx.monomorphize(&base_ty);
 
                 // ZSTs don't require any actual memory access.
-                let elem_ty = base_ty.projection_ty(cx.tcx(), elem).ty;
-                let elem_ty = self.fx.monomorphize(&elem_ty);
+                let elem_ty = base_ty.projection_ty(cx.tcx(), self.fx.monomorphize(&elem)).ty;
                 let span = self.fx.mir.local_decls[place_ref.local].source_info.span;
                 if cx.spanned_layout_of(elem_ty, span).is_zst() {
                     return;
diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs
index 7116bb8c925..e1de9677f80 100644
--- a/src/librustc_codegen_ssa/mir/block.rs
+++ b/src/librustc_codegen_ssa/mir/block.rs
@@ -543,7 +543,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 Some(
                     ty::Instance::resolve(bx.tcx(), ty::ParamEnv::reveal_all(), def_id, substs)
                         .unwrap()
-                        .unwrap(),
+                        .unwrap()
+                        .polymorphize(bx.tcx()),
                 ),
                 None,
             ),
diff --git a/src/librustc_codegen_ssa/mir/rvalue.rs b/src/librustc_codegen_ssa/mir/rvalue.rs
index 4b2be7b5321..9c108998bc9 100644
--- a/src/librustc_codegen_ssa/mir/rvalue.rs
+++ b/src/librustc_codegen_ssa/mir/rvalue.rs
@@ -190,17 +190,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                 if bx.cx().tcx().has_attr(def_id, sym::rustc_args_required_const) {
                                     bug!("reifying a fn ptr that requires const arguments");
                                 }
-                                OperandValue::Immediate(
-                                    bx.get_fn_addr(
-                                        ty::Instance::resolve_for_fn_ptr(
-                                            bx.tcx(),
-                                            ty::ParamEnv::reveal_all(),
-                                            def_id,
-                                            substs,
-                                        )
-                                        .unwrap(),
-                                    ),
+                                let instance = ty::Instance::resolve_for_fn_ptr(
+                                    bx.tcx(),
+                                    ty::ParamEnv::reveal_all(),
+                                    def_id,
+                                    substs,
                                 )
+                                .unwrap()
+                                .polymorphize(bx.cx().tcx());
+                                OperandValue::Immediate(bx.get_fn_addr(instance))
                             }
                             _ => bug!("{} cannot be reified to a fn ptr", operand.layout.ty),
                         }
@@ -213,7 +211,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                     def_id,
                                     substs,
                                     ty::ClosureKind::FnOnce,
-                                );
+                                )
+                                .polymorphize(bx.cx().tcx());
                                 OperandValue::Immediate(bx.cx().get_fn_addr(instance))
                             }
                             _ => bug!("{} cannot be cast to a fn ptr", operand.layout.ty),