Remove -Zthinlto

This explicitly enables thin local LTO. It was added before support for
this got stabilized and implicitly enabled when optimizations are
enabled. All tests that use it already implicitly enable this option.

Author: bjorn3

compiler/rustc_interface/src/tests.rs

@@ -872,7 +872,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(src_hash_algorithm, Some(SourceFileHashAlgorithm::Sha1));
     tracked!(stack_protector, StackProtector::All);
     tracked!(teach, true);
-    tracked!(thinlto, Some(true));
     tracked!(tiny_const_eval_limit, true);
     tracked!(tls_model, Some(TlsModel::GeneralDynamic));
     tracked!(translate_remapped_path_to_local_path, false);

compiler/rustc_session/src/options.rs

@@ -2685,9 +2685,6 @@ written to standard error output)"),
         "the directory the intermediate files are written to"),
     terminal_urls: TerminalUrl = (TerminalUrl::No, parse_terminal_url, [UNTRACKED],
         "use the OSC 8 hyperlink terminal specification to print hyperlinks in the compiler output"),
-    #[rustc_lint_opt_deny_field_access("use `Session::lto` instead of this field")]
-    thinlto: Option<bool> = (None, parse_opt_bool, [TRACKED],
-        "enable ThinLTO when possible"),
     /// We default to 1 here since we want to behave like
     /// a sequential compiler for now. This'll likely be adjusted
     /// in the future. Note that -Zthreads=0 is the way to get

compiler/rustc_session/src/session.rs

@@ -628,19 +628,6 @@ impl Session {
             return config::Lto::No;
         }
 
-        // If `-Z thinlto` specified process that, but note that this is mostly
-        // a deprecated option now that `-C lto=thin` exists.
-        if let Some(enabled) = self.opts.unstable_opts.thinlto {
-            if enabled {
-                if !self.thin_lto_supported {
-                    self.dcx().emit_fatal(errors::ThinLtoNotSupportedByBackend);
-                }
-                return config::Lto::ThinLocal;
-            } else {
-                return config::Lto::No;
-            }
-        }
-
         // If there's only one codegen unit and LTO isn't enabled then there's
         // no need for ThinLTO so just return false.
         if self.codegen_units().as_usize() == 1 {

tests/ui/README.md

@@ -903,7 +903,7 @@ Tests on [AST lowering](https://rustc-dev-guide.rust-lang.org/ast-lowering.html)
 
 ## `tests/ui/lto/`
 
-Exercise *Link-Time Optimization* (LTO), involving the flags `-C lto` or `-Z thinlto`.
+Exercise *Link-Time Optimization* (LTO), involving the flags `-C lto`.
 
 ## `tests/ui/lub-glb/`: LUB/GLB algorithm update
 

tests/ui/lto/auxiliary/dylib.rs

@@ -1,4 +1,4 @@
-//@ compile-flags: -Z thinlto -C codegen-units=8
+//@ compile-flags: -C codegen-units=8
 
 #[inline]
 pub fn foo(b: u8) {

tests/ui/lto/auxiliary/msvc-imp-present.rs

@@ -1,5 +1,5 @@
 //@ no-prefer-dynamic
-//@ compile-flags: -Z thinlto -C codegen-units=8 -C prefer-dynamic
+//@ compile-flags: -C codegen-units=8 -C prefer-dynamic
 
 #![crate_type = "rlib"]
 #![crate_type = "dylib"]

tests/ui/lto/msvc-imp-present.rs

@@ -1,7 +1,7 @@
 //@ run-pass
 
 //@ aux-build:msvc-imp-present.rs
-//@ compile-flags: -Z thinlto -C codegen-units=8
+//@ compile-flags: -C codegen-units=8
 //@ no-prefer-dynamic
 
 // On MSVC we have a "hack" where we emit symbols that look like `_imp_$name`

tests/ui/lto/thin-lto-global-allocator.rs

@@ -1,5 +1,5 @@
 //@ run-pass
-//@ compile-flags: -Z thinlto -C codegen-units=2
+//@ compile-flags: -C codegen-units=2
 
 #[global_allocator]
 static A: std::alloc::System = std::alloc::System;

tests/ui/lto/thin-lto-inlines.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 
-//@ compile-flags: -Z thinlto -C codegen-units=8 -O
+//@ compile-flags: -C codegen-units=8 -O
 //@ ignore-emscripten can't inspect instructions on emscripten
 
 // We want to assert here that ThinLTO will inline across codegen units. There's

tests/ui/lto/weak-works.rs

@@ -1,6 +1,6 @@
 //@ run-pass
 
-//@ compile-flags: -C codegen-units=8 -Z thinlto
+//@ compile-flags: -C codegen-units=8
 //@ ignore-i686-pc-windows-gnu
 //@ ignore-x86_64-pc-windows-gnu