Attempt to fix Thin LTO

Author: antoyo

src/back/write.rs

@@ -1,6 +1,6 @@
 use std::{env, fs};
 
-use gccjit::{Context, OutputKind};
+use gccjit::OutputKind;
 use rustc_codegen_ssa::back::link::ensure_removed;
 use rustc_codegen_ssa::back::write::{BitcodeSection, CodegenContext, EmitObj, ModuleConfig};
 use rustc_codegen_ssa::{CompiledModule, ModuleCodegen};
@@ -11,7 +11,6 @@ use rustc_log::tracing::debug;
 use rustc_session::config::OutputType;
 use rustc_target::spec::SplitDebuginfo;
 
-use crate::base::add_pic_option;
 use crate::errors::CopyBitcode;
 use crate::{GccContext, LtoMode};
 
@@ -148,7 +147,6 @@ pub(crate) fn codegen(
                     let path = obj_out.to_str().expect("path to str");
 
                     if fat_lto {
-                        let lto_path = format!("{}.lto", path);
                         // cSpell:disable
                         // FIXME(antoyo): The LTO frontend generates the following warning:
                         // ../build_sysroot/sysroot_src/library/core/src/num/dec2flt/lemire.rs:150:15: warning: type of ‘_ZN4core3num7dec2flt5table17POWER_OF_FIVE_12817ha449a68fb31379e4E’ does not match original declaration [-Wlto-type-mismatch]
@@ -159,27 +157,6 @@ pub(crate) fn codegen(
                         // This option is to mute it to make the UI tests pass with LTO enabled.
                         // cSpell:enable
                         context.add_driver_option("-Wno-lto-type-mismatch");
-                        // NOTE: this doesn't actually generate an executable. With the above
-                        // flags, it combines the .o files together in another .o.
-                        context.compile_to_file(OutputKind::Executable, &lto_path);
-
-                        let context = Context::default();
-                        if cgcx.target_arch == "x86" || cgcx.target_arch == "x86_64" {
-                            // NOTE: it seems we need to use add_driver_option instead of
-                            // add_command_line_option here because we use the LTO frontend via gcc.
-                            context.add_driver_option("-masm=intel");
-                        }
-
-                        // NOTE: these two options are needed to invoke LTO to produce an object file.
-                        // We need to initiate a second compilation because the arguments "-x lto"
-                        // needs to be at the very beginning.
-                        context.add_driver_option("-x");
-                        context.add_driver_option("lto");
-                        add_pic_option(&context, module.module_llvm.relocation_model);
-                        context.add_driver_option(lto_path);
-
-                        context.compile_to_file(OutputKind::ObjectFile, path);
-                    } else {
                         // NOTE: this doesn't actually generate an executable. With the above
                         // flags, it combines the .o files together in another .o.
                         context.compile_to_file(OutputKind::Executable, path);

src/lib.rs

@@ -384,6 +384,7 @@ pub struct GccContext {
     context: Arc<SyncContext>,
     /// This field is needed in order to be able to set the flag -fPIC when necessary when doing
     /// LTO.
+    #[allow(dead_code)]
     relocation_model: RelocModel,
     lto_mode: LtoMode,
     lto_supported: bool,