Cleanup lto dead code

.github/workflows/release.yml

@@ -62,7 +62,7 @@ jobs:
     - name: Build
       run: |
         ./y.sh prepare --only-libcore
-        EMBED_LTO_BITCODE=1 ./y.sh build --sysroot --release --release-sysroot
+        ./y.sh build --sysroot --release --release-sysroot
         ./y.sh test --cargo-tests
         ./y.sh clean all
 
@@ -77,14 +77,12 @@ jobs:
 
     - name: Run tests
       run: |
-        # FIXME(antoyo): we cannot enable LTO for stdarch tests currently because of some failing LTO tests using proc-macros.
-        # FIXME(antoyo): this should probably not be needed since we embed the LTO bitcode.
         printf '[profile.release]\nlto = "fat"\n' >> build/build_sysroot/sysroot_src/library/Cargo.toml
-        EMBED_LTO_BITCODE=1 ./y.sh test --release --clean --release-sysroot --build-sysroot --keep-lto-tests ${{ matrix.commands }}
+        ./y.sh test --release --clean --release-sysroot --build-sysroot --keep-lto-tests ${{ matrix.commands }}
 
     - name: Run y.sh cargo build
       run: |
-        EMBED_LTO_BITCODE=1 CHANNEL="release" ./y.sh cargo build --release --manifest-path tests/hello-world/Cargo.toml
+        CHANNEL="release" ./y.sh cargo build --release --manifest-path tests/hello-world/Cargo.toml
         call_found=$(objdump -dj .text tests/hello-world/target/release/hello_world | grep -c "call .*mylib.*my_func" ) ||:
         if [ $call_found -gt 0 ]; then
           echo "ERROR: call my_func found in asm"

Readme.md

@@ -137,13 +137,7 @@ If you compiled cg_gccjit in debug mode (aka you didn't pass `--release` to `./y
 
 ### LTO
 
-To use LTO, you need to set the variable `EMBED_LTO_BITCODE=1` in addition to setting `lto = "fat"` in the `Cargo.toml`.
-
-Failing to set `EMBED_LTO_BITCODE` will give you the following error:
-
-```
-error: failed to copy bitcode to object file: No such file or directory (os error 2)
-```
+To use LTO, you need to set `lto = "fat"` in the `Cargo.toml`.
 
 ### Rustc
 

src/back/lto.rs

@@ -33,7 +33,6 @@ use rustc_errors::{DiagCtxtHandle, FatalError};
 use rustc_middle::bug;
 use rustc_middle::dep_graph::WorkProduct;
 use rustc_session::config::Lto;
-use rustc_target::spec::RelocModel;
 use tempfile::{TempDir, tempdir};
 
 use crate::back::write::save_temp_bitcode;
@@ -566,13 +565,7 @@ pub fn optimize_thin_module(
     };
     let module = ModuleCodegen::new_regular(
         thin_module.name().to_string(),
-        GccContext {
-            context,
-            should_combine_object_files,
-            // TODO(antoyo): use the correct relocation model here.
-            relocation_model: RelocModel::Pic,
-            temp_dir: None,
-        },
+        GccContext { context, should_combine_object_files, temp_dir: None },
     );
     /*{
         let target = &*module.module_llvm.tm;

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};
@@ -9,7 +9,6 @@ use rustc_session::config::OutputType;
 use rustc_span::fatal_error::FatalError;
 use rustc_target::spec::SplitDebuginfo;
 
-use crate::base::add_pic_option;
 use crate::errors::CopyBitcode;
 use crate::{GccCodegenBackend, GccContext};
 
@@ -27,11 +26,6 @@ pub(crate) fn codegen(
 
         let should_combine_object_files = module.module_llvm.should_combine_object_files;
 
-        // NOTE: Only generate object files with GIMPLE when this environment variable is set for
-        // now because this requires a particular setup (same gcc/lto1/lto-wrapper commit as libgccjit).
-        // TODO(antoyo): remove this environment variable.
-        let fat_lto = env::var("EMBED_LTO_BITCODE").as_deref() == Ok("1");
-
         let bc_out = cgcx.output_filenames.temp_path_for_cgu(
             OutputType::Bitcode,
             &module.name,
@@ -44,80 +38,24 @@ pub(crate) fn codegen(
         );
 
         if config.bitcode_needed() {
-            if fat_lto {
+            if config.emit_bc || config.emit_obj == EmitObj::Bitcode {
                 let _timer = cgcx
                     .prof
-                    .generic_activity_with_arg("GCC_module_codegen_make_bitcode", &*module.name);
-
-                // TODO(antoyo)
-                /*if let Some(bitcode_filename) = bc_out.file_name() {
-                    cgcx.prof.artifact_size(
-                        "llvm_bitcode",
-                        bitcode_filename.to_string_lossy(),
-                        data.len() as u64,
-                    );
-                }*/
-
-                if config.emit_bc || config.emit_obj == EmitObj::Bitcode {
-                    let _timer = cgcx.prof.generic_activity_with_arg(
-                        "GCC_module_codegen_emit_bitcode",
-                        &*module.name,
-                    );
-                    context.add_command_line_option("-flto=auto");
-                    context.add_command_line_option("-flto-partition=one");
-                    // TODO(antoyo): remove since we don't want fat objects when it is for Bitcode only.
-                    context.add_command_line_option("-ffat-lto-objects");
-                    context.compile_to_file(
-                        OutputKind::ObjectFile,
-                        bc_out.to_str().expect("path to str"),
-                    );
-                }
-
-                if config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full) {
-                    let _timer = cgcx.prof.generic_activity_with_arg(
-                        "GCC_module_codegen_embed_bitcode",
-                        &*module.name,
-                    );
-                    // TODO(antoyo): maybe we should call embed_bitcode to have the proper iOS fixes?
-                    //embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, data);
-
-                    context.add_command_line_option("-flto=auto");
-                    context.add_command_line_option("-flto-partition=one");
-                    context.add_command_line_option("-ffat-lto-objects");
-                    // TODO(antoyo): Send -plugin/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/liblto_plugin.so to linker (this should be done when specifying the appropriate rustc cli argument).
-                    context.compile_to_file(
-                        OutputKind::ObjectFile,
-                        bc_out.to_str().expect("path to str"),
-                    );
-                }
-            } else {
-                if config.emit_bc || config.emit_obj == EmitObj::Bitcode {
-                    let _timer = cgcx.prof.generic_activity_with_arg(
-                        "GCC_module_codegen_emit_bitcode",
-                        &*module.name,
-                    );
-                    context.compile_to_file(
-                        OutputKind::ObjectFile,
-                        bc_out.to_str().expect("path to str"),
-                    );
-                }
+                    .generic_activity_with_arg("GCC_module_codegen_emit_bitcode", &*module.name);
+                context
+                    .compile_to_file(OutputKind::ObjectFile, bc_out.to_str().expect("path to str"));
+            }
 
-                if config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full) {
-                    // TODO(antoyo): we might want to emit to emit an error here, saying to set the
-                    // environment variable EMBED_LTO_BITCODE.
-                    let _timer = cgcx.prof.generic_activity_with_arg(
-                        "GCC_module_codegen_embed_bitcode",
-                        &*module.name,
-                    );
-                    // TODO(antoyo): maybe we should call embed_bitcode to have the proper iOS fixes?
-                    //embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, data);
+            if config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full) {
+                let _timer = cgcx
+                    .prof
+                    .generic_activity_with_arg("GCC_module_codegen_embed_bitcode", &*module.name);
+                // TODO(antoyo): maybe we should call embed_bitcode to have the proper iOS fixes?
+                //embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, data);
 
-                    // TODO(antoyo): Send -plugin/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/liblto_plugin.so to linker (this should be done when specifying the appropriate rustc cli argument).
-                    context.compile_to_file(
-                        OutputKind::ObjectFile,
-                        bc_out.to_str().expect("path to str"),
-                    );
-                }
+                // TODO(antoyo): Send -plugin/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/liblto_plugin.so to linker (this should be done when specifying the appropriate rustc cli argument).
+                context
+                    .compile_to_file(OutputKind::ObjectFile, bc_out.to_str().expect("path to str"));
             }
         }
 
@@ -167,61 +105,16 @@ pub(crate) fn codegen(
                     context.dump_to_file(path, true);
                 }
                 if should_combine_object_files {
-                    if fat_lto {
-                        context.add_command_line_option("-flto=auto");
-                        context.add_command_line_option("-flto-partition=one");
-
-                        // NOTE: without -fuse-linker-plugin, we get the following error:
-                        // lto1: internal compiler error: decompressed stream: Destination buffer is too small
-                        // TODO(antoyo): since we do not do LTO when the linker is invoked anymore, perhaps
-                        // the following flag is not necessary anymore.
-                        context.add_driver_option("-fuse-linker-plugin");
-                    }
-
                     context.add_driver_option("-Wl,-r");
                     // NOTE: we need -nostdlib, otherwise, we get the following error:
                     // /usr/bin/ld: cannot find -lgcc_s: No such file or directory
                     context.add_driver_option("-nostdlib");
 
                     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]
-                        // 150 |     let (lo5, hi5) = POWER_OF_FIVE_128[index];
-                        //     |               ^
-                        // lto1: note: ‘_ZN4core3num7dec2flt5table17POWER_OF_FIVE_12817ha449a68fb31379e4E’ was previously declared here
-                        //
-                        // 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);
-                    }
+                    // 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);
                 } else {
                     context.compile_to_file(
                         OutputKind::ObjectFile,

src/base.rs

@@ -246,7 +246,6 @@ pub fn compile_codegen_unit(
             cgu_name.to_string(),
             GccContext {
                 context: Arc::new(SyncContext::new(context)),
-                relocation_model: tcx.sess.relocation_model(),
                 should_combine_object_files: false,
                 temp_dir: None,
             },

src/lib.rs

@@ -112,7 +112,6 @@ use rustc_session::Session;
 use rustc_session::config::{OptLevel, OutputFilenames};
 use rustc_span::Symbol;
 use rustc_span::fatal_error::FatalError;
-use rustc_target::spec::RelocModel;
 use tempfile::TempDir;
 
 use crate::back::lto::ModuleBuffer;
@@ -287,7 +286,6 @@ impl ExtraBackendMethods for GccCodegenBackend {
     ) -> Self::Module {
         let mut mods = GccContext {
             context: Arc::new(SyncContext::new(new_context(tcx))),
-            relocation_model: tcx.sess.relocation_model(),
             should_combine_object_files: false,
             temp_dir: None,
         };
@@ -319,9 +317,6 @@ impl ExtraBackendMethods for GccCodegenBackend {
 
 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.
-    relocation_model: RelocModel,
     should_combine_object_files: bool,
     // Temporary directory used by LTO. We keep it here so that it's not removed before linking.
     temp_dir: Option<TempDir>,