Add back error for ThinLTO

Author: antoyo

build_sysroot/Cargo.toml

@@ -17,4 +17,5 @@ rustc-std-workspace-std = { path = "./sysroot_src/library/rustc-std-workspace-st
 
 [profile.release]
 debug = true
+# FIXME: is this actually needed?
 lto = "fat"

locales/en-US.ftl

@@ -2,7 +2,7 @@ codegen_gcc_unwinding_inline_asm =
     GCC backend does not support unwinding from inline asm
 
 codegen_gcc_lto_not_supported =
-    LTO is not supported. You may get a linker error.
+    Thin LTO is not supported. You may get a linker error.
 
 codegen_gcc_invalid_monomorphization_basic_integer =
     invalid monomorphization of `{$name}` intrinsic: expected basic integer type, found `{$ty}`

src/back/lto.rs

@@ -1,3 +1,7 @@
+// FIXME:
+// fat-lto UI test fail with:
+// x86_64-pc-linux-gnu-gcc-13.1.0: fatal error: ‘-fuse-linker-plugin’, but liblto_plugin.so not found
+//
 // Fix these warnings:
 // /usr/bin/ld: warning: type of symbol `_RNvNvNvNtCs5JWOrf9uCus_5rayon11thread_pool19WORKER_THREAD_STATE7___getit5___KEY' changed from 1 to 6 in /tmp/ccKeUSiR.ltrans0.ltrans.o
 // /usr/bin/ld: warning: type of symbol `_RNvNvNvNvNtNtNtCsAj5i4SGTR7_3std4sync4mpmc5waker17current_thread_id5DUMMY7___getit5___KEY' changed from 1 to 6 in /tmp/ccKeUSiR.ltrans0.ltrans.o

src/lib.rs

@@ -1,9 +1,9 @@
-// TODO: rebase on master.
-
 /*
  * TODO(antoyo): implement equality in libgccjit based on https://zpz.github.io/blog/overloading-equality-operator-in-cpp-class-hierarchy/ (for type equality?)
  * TODO(antoyo): support #[inline] attributes.
  * TODO(antoyo): support LTO (gcc's equivalent to Full LTO is -flto -flto-partition=one — https://documentation.suse.com/sbp/all/html/SBP-GCC-10/index.html).
+ * For Thin LTO, this might be helpful:
+ * In gcc 4.6 -fwhopr was removed and became default with -flto. The non-whopr path can still be executed via -flto-partition=none.
  *
  * TODO(antoyo): remove the patches.
  */
@@ -71,6 +71,7 @@ use std::any::Any;
 use std::sync::atomic::AtomicBool;
 use std::sync::{Arc, Mutex};
 
+use errors::LTONotSupported;
 use gccjit::{Context, OptimizationLevel, CType};
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen};
@@ -86,7 +87,7 @@ use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::query::Providers;
-use rustc_session::config::{OptLevel, OutputFilenames};
+use rustc_session::config::{Lto, OptLevel, OutputFilenames};
 use rustc_session::Session;
 use rustc_span::Symbol;
 use rustc_span::fatal_error::FatalError;
@@ -117,9 +118,12 @@ impl CodegenBackend for GccCodegenBackend {
         crate::DEFAULT_LOCALE_RESOURCE
     }
 
-    fn init(&self, _sess: &Session) {
+    fn init(&self, sess: &Session) {
         #[cfg(feature="master")]
         gccjit::set_global_personality_function_name(b"rust_eh_personality\0");
+        if sess.lto() == Lto::Thin {
+            sess.emit_warning(LTONotSupported {});
+        }
 
         let temp_dir = TempDir::new().expect("cannot create temporary directory");
         let temp_file = temp_dir.into_path().join("result.asm");