Auto merge of #125507 - compiler-errors:type-length-limit, r=lcnr

Re-implement a type-size based limit

r? lcnr

This PR reintroduces the type length limit added in #37789, which was accidentally made practically useless by the caching changes to `Ty::walk` in #72412, which caused the `walk` function to no longer walk over identical elements.

Hitting this length limit is not fatal unless we are in codegen -- so it shouldn't affect passes like the mir inliner which creates potentially very large types (which we observed, for example, when the new trait solver compiles `itertools` in `--release` mode).

This also increases the type length limit from `1048576 == 2 ** 20` to `2 ** 24`, which covers all of the code that can be reached with craterbot-check. Individual crates can increase the length limit further if desired.

Perf regression is mild and I think we should accept it -- reinstating this limit is important for the new trait solver and to make sure we don't accidentally hit more type-size related regressions in the future.

Fixes #125460

compiler/rustc_codegen_ssa/src/base.rs

@@ -37,7 +37,7 @@ use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_session::config::{self, CrateType, EntryFnType, OptLevel, OutputType};
 use rustc_session::Session;
 use rustc_span::symbol::sym;
-use rustc_span::Symbol;
+use rustc_span::{Symbol, DUMMY_SP};
 use rustc_target::abi::FIRST_VARIANT;
 
 use std::cmp;
@@ -467,6 +467,7 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
                 ty::ParamEnv::reveal_all(),
                 start_def_id,
                 cx.tcx().mk_args(&[main_ret_ty.into()]),
+                DUMMY_SP,
             );
             let start_fn = cx.get_fn_addr(start_instance);
 

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -842,6 +842,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         ty::ParamEnv::reveal_all(),
                         def_id,
                         args,
+                        fn_span,
                     )
                     .polymorphize(bx.tcx()),
                 ),