From 660d1e207b726f05c7f93fe238f9452ccba37c09 Mon Sep 17 00:00:00 2001 From: Flakebi Date: Fri, 28 Mar 2025 10:15:56 +0100 Subject: [PATCH] Fix linker-plugin-lto only doing thin lto When rust provides LLVM bitcode files to lld and the bitcode contains function summaries as used for thin lto, lld defaults to using thin lto. This prevents some optimizations that are only applied for fat lto. We solve this by not creating function summaries when fat lto is enabled. The bitcode for the module is just directly written out. An alternative solution would be to set the `ThinLTO=0` module flag to signal lld to do fat lto. The code in clang that sets this flag is here: https://github.com/llvm/llvm-project/blob/560149b5e3c891c64899e9912e29467a69dc3a4c/clang/lib/CodeGen/BackendUtil.cpp#L1150 The code in LLVM that queries the flag and defaults to thin lto if not set is here: https://github.com/llvm/llvm-project/blob/e258bca9505f35e0a22cb213a305eea9b76d11ea/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp#L4441-L4446 --- compiler/rustc_codegen_llvm/src/back/write.rs | 2 +- .../src/external_deps/llvm.rs | 30 +++++++++++++++++ .../src/external_deps/rustc.rs | 6 ++++ src/tools/run-make-support/src/lib.rs | 2 +- tests/run-make/cross-lang-lto-clang/rmake.rs | 27 ++++++++++++---- tests/run-make/fat-then-thin-lto/lib.rs | 8 +++++ tests/run-make/fat-then-thin-lto/main.rs | 11 +++++++ tests/run-make/fat-then-thin-lto/rmake.rs | 25 +++++++++++++++ tests/run-make/linker-plugin-lto-fat/ir.ll | 6 ++++ tests/run-make/linker-plugin-lto-fat/main.rs | 17 ++++++++++ tests/run-make/linker-plugin-lto-fat/rmake.rs | 32 +++++++++++++++++++ 11 files changed, 157 insertions(+), 9 deletions(-) create mode 100644 tests/run-make/fat-then-thin-lto/lib.rs create mode 100644 tests/run-make/fat-then-thin-lto/main.rs create mode 100644 tests/run-make/fat-then-thin-lto/rmake.rs create mode 100644 tests/run-make/linker-plugin-lto-fat/ir.ll create mode 100644 tests/run-make/linker-plugin-lto-fat/main.rs create mode 100644 tests/run-make/linker-plugin-lto-fat/rmake.rs diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs index bead4c82a8120..0fe41f6801eef 100644 --- a/compiler/rustc_codegen_llvm/src/back/write.rs +++ b/compiler/rustc_codegen_llvm/src/back/write.rs @@ -827,7 +827,7 @@ pub(crate) unsafe fn codegen( "LLVM_module_codegen_make_bitcode", &*module.name, ); - ThinBuffer::new(llmod, config.emit_thin_lto, false) + ThinBuffer::new(llmod, cgcx.lto != Lto::Fat && config.emit_thin_lto, false) }; let data = thin.data(); let _timer = cgcx diff --git a/src/tools/run-make-support/src/external_deps/llvm.rs b/src/tools/run-make-support/src/external_deps/llvm.rs index 9a6e35da3fe20..939160d9f41d8 100644 --- a/src/tools/run-make-support/src/external_deps/llvm.rs +++ b/src/tools/run-make-support/src/external_deps/llvm.rs @@ -60,6 +60,12 @@ pub fn llvm_pdbutil() -> LlvmPdbutil { LlvmPdbutil::new() } +/// Construct a new `llvm-as` invocation. This assumes that `llvm-as` is available +/// at `$LLVM_BIN_DIR/llvm-as`. +pub fn llvm_as() -> LlvmAs { + LlvmAs::new() +} + /// Construct a new `llvm-dis` invocation. This assumes that `llvm-dis` is available /// at `$LLVM_BIN_DIR/llvm-dis`. pub fn llvm_dis() -> LlvmDis { @@ -135,6 +141,13 @@ pub struct LlvmPdbutil { cmd: Command, } +/// A `llvm-as` invocation builder. +#[derive(Debug)] +#[must_use] +pub struct LlvmAs { + cmd: Command, +} + /// A `llvm-dis` invocation builder. #[derive(Debug)] #[must_use] @@ -158,6 +171,7 @@ crate::macros::impl_common_helpers!(LlvmNm); crate::macros::impl_common_helpers!(LlvmBcanalyzer); crate::macros::impl_common_helpers!(LlvmDwarfdump); crate::macros::impl_common_helpers!(LlvmPdbutil); +crate::macros::impl_common_helpers!(LlvmAs); crate::macros::impl_common_helpers!(LlvmDis); crate::macros::impl_common_helpers!(LlvmObjcopy); @@ -441,6 +455,22 @@ impl LlvmObjcopy { } } +impl LlvmAs { + /// Construct a new `llvm-as` invocation. This assumes that `llvm-as` is available + /// at `$LLVM_BIN_DIR/llvm-as`. + pub fn new() -> Self { + let llvm_as = llvm_bin_dir().join("llvm-as"); + let cmd = Command::new(llvm_as); + Self { cmd } + } + + /// Provide an input file. + pub fn input>(&mut self, path: P) -> &mut Self { + self.cmd.arg(path.as_ref()); + self + } +} + impl LlvmDis { /// Construct a new `llvm-dis` invocation. This assumes that `llvm-dis` is available /// at `$LLVM_BIN_DIR/llvm-dis`. diff --git a/src/tools/run-make-support/src/external_deps/rustc.rs b/src/tools/run-make-support/src/external_deps/rustc.rs index 0e2239147f122..e6ea1330e4a8b 100644 --- a/src/tools/run-make-support/src/external_deps/rustc.rs +++ b/src/tools/run-make-support/src/external_deps/rustc.rs @@ -171,6 +171,12 @@ impl Rustc { self } + /// This flag enables LTO in the specified form. + pub fn lto(&mut self, option: &str) -> &mut Self { + self.cmd.arg(format!("-Clto={option}")); + self + } + /// This flag defers LTO optimizations to the linker. pub fn linker_plugin_lto(&mut self, option: &str) -> &mut Self { self.cmd.arg(format!("-Clinker-plugin-lto={option}")); diff --git a/src/tools/run-make-support/src/lib.rs b/src/tools/run-make-support/src/lib.rs index e0ad3ee9bedaa..f7cffea82cb46 100644 --- a/src/tools/run-make-support/src/lib.rs +++ b/src/tools/run-make-support/src/lib.rs @@ -63,7 +63,7 @@ pub use cargo::cargo; pub use clang::{clang, Clang}; pub use htmldocck::htmldocck; pub use llvm::{ - llvm_ar, llvm_bcanalyzer, llvm_dis, llvm_dwarfdump, llvm_filecheck, llvm_nm, llvm_objcopy, + llvm_ar, llvm_bcanalyzer, llvm_as, llvm_dis, llvm_dwarfdump, llvm_filecheck, llvm_nm, llvm_objcopy, llvm_objdump, llvm_profdata, llvm_readobj, LlvmAr, LlvmBcanalyzer, LlvmDis, LlvmDwarfdump, LlvmFilecheck, LlvmNm, LlvmObjcopy, LlvmObjdump, LlvmProfdata, LlvmReadobj, }; diff --git a/tests/run-make/cross-lang-lto-clang/rmake.rs b/tests/run-make/cross-lang-lto-clang/rmake.rs index 3fed6ea20667a..0c4383e2cd815 100644 --- a/tests/run-make/cross-lang-lto-clang/rmake.rs +++ b/tests/run-make/cross-lang-lto-clang/rmake.rs @@ -28,7 +28,16 @@ static C_NEVER_INLINED_PATTERN: &'static str = "bl.*"; static C_NEVER_INLINED_PATTERN: &'static str = "call.*c_never_inlined"; fn main() { + test_lto(false); + test_lto(true); +} + +fn test_lto(fat_lto: bool) { + let lto = if fat_lto { "fat" } else { "thin" }; + let clang_lto = if fat_lto { "full" } else { "thin" }; + rustc() + .lto(lto) .linker_plugin_lto("on") .output(static_lib_name("rustlib-xlto")) .opt_level("2") @@ -36,7 +45,7 @@ fn main() { .input("rustlib.rs") .run(); clang() - .lto("thin") + .lto(clang_lto) .use_ld("lld") .arg("-lrustlib-xlto") .out_exe("cmain") @@ -57,9 +66,10 @@ fn main() { .input("cmain") .run() .assert_stdout_contains_regex(RUST_NEVER_INLINED_PATTERN); - clang().input("clib.c").lto("thin").arg("-c").out_exe("clib.o").arg("-O2").run(); + clang().input("clib.c").lto(clang_lto).arg("-c").out_exe("clib.o").arg("-O2").run(); llvm_ar().obj_to_ar().output_input(static_lib_name("xyz"), "clib.o").run(); rustc() + .lto(lto) .linker_plugin_lto("on") .opt_level("2") .linker(&env_var("CLANG")) @@ -72,9 +82,12 @@ fn main() { .input("rsmain") .run() .assert_stdout_not_contains_regex(C_ALWAYS_INLINED_PATTERN); - llvm_objdump() - .disassemble() - .input("rsmain") - .run() - .assert_stdout_contains_regex(C_NEVER_INLINED_PATTERN); + + let dump = llvm_objdump().disassemble().input("rsmain").run(); + if !fat_lto { + dump.assert_stdout_contains_regex(C_NEVER_INLINED_PATTERN); + } else { + // fat lto inlines this anyway + dump.assert_stdout_not_contains_regex(C_NEVER_INLINED_PATTERN); + } } diff --git a/tests/run-make/fat-then-thin-lto/lib.rs b/tests/run-make/fat-then-thin-lto/lib.rs new file mode 100644 index 0000000000000..3091988368628 --- /dev/null +++ b/tests/run-make/fat-then-thin-lto/lib.rs @@ -0,0 +1,8 @@ +#![feature(no_core, lang_items)] +#![no_core] +#![crate_type = "rlib"] + +#[lang = "sized"] +trait Sized {} + +pub fn foo() {} diff --git a/tests/run-make/fat-then-thin-lto/main.rs b/tests/run-make/fat-then-thin-lto/main.rs new file mode 100644 index 0000000000000..a3f2e18158bc0 --- /dev/null +++ b/tests/run-make/fat-then-thin-lto/main.rs @@ -0,0 +1,11 @@ +#![allow(internal_features)] +#![feature(no_core, lang_items)] +#![no_core] +#![crate_type = "cdylib"] + +extern crate lib; + +#[unsafe(no_mangle)] +pub fn bar() { + lib::foo(); +} diff --git a/tests/run-make/fat-then-thin-lto/rmake.rs b/tests/run-make/fat-then-thin-lto/rmake.rs new file mode 100644 index 0000000000000..ef4f26689d4e8 --- /dev/null +++ b/tests/run-make/fat-then-thin-lto/rmake.rs @@ -0,0 +1,25 @@ +// Compile a library with lto=fat, then compile a binary with lto=thin +// and check that lto is applied with the library. +// The goal is to mimic the standard library being build with lto=fat +// and allowing users to build with lto=thin. + +//@ only-x86_64-unknown-linux-gnu + +use run_make_support::{dynamic_lib_name, llvm_objdump, rustc}; + +fn main() { + rustc().input("lib.rs").opt_level("3").lto("fat").run(); + rustc().input("main.rs").panic("abort").opt_level("3").lto("thin").run(); + + llvm_objdump() + .input(dynamic_lib_name("main")) + .arg("--disassemble-symbols=bar") + .run() + // The called function should be inlined. + // Check that we have a ret (to detect tail + // calls with a jmp) and no call. + .assert_stdout_contains("bar") + .assert_stdout_contains("ret") + .assert_stdout_not_contains("foo") + .assert_stdout_not_contains("call"); +} diff --git a/tests/run-make/linker-plugin-lto-fat/ir.ll b/tests/run-make/linker-plugin-lto-fat/ir.ll new file mode 100644 index 0000000000000..fa3dbdd4e088d --- /dev/null +++ b/tests/run-make/linker-plugin-lto-fat/ir.ll @@ -0,0 +1,6 @@ +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-unknown-linux-gnu" + +define void @ir_callee() { + ret void +} diff --git a/tests/run-make/linker-plugin-lto-fat/main.rs b/tests/run-make/linker-plugin-lto-fat/main.rs new file mode 100644 index 0000000000000..3a7b02f4b92e3 --- /dev/null +++ b/tests/run-make/linker-plugin-lto-fat/main.rs @@ -0,0 +1,17 @@ +#![feature(no_core, lang_items)] +#![no_core] +#![crate_type = "cdylib"] + +#[lang = "sized"] +trait Sized {} + +extern "C" { + fn ir_callee(); +} + +#[no_mangle] +extern "C" fn rs_foo() { + unsafe { + ir_callee(); + } +} diff --git a/tests/run-make/linker-plugin-lto-fat/rmake.rs b/tests/run-make/linker-plugin-lto-fat/rmake.rs new file mode 100644 index 0000000000000..0cfc799d2aaa1 --- /dev/null +++ b/tests/run-make/linker-plugin-lto-fat/rmake.rs @@ -0,0 +1,32 @@ +// Check that -C lto=fat with -C linker-plugin-lto actually works and can inline functions. +// A library is created from LLVM IR, defining a single function. Then a dylib is compiled, +// linking to the library and calling the function from the library. +// The function from the library should end up inlined and disappear from the output. + +//@ only-x86_64-unknown-linux-gnu +//@ needs-rust-lld + +use run_make_support::{dynamic_lib_name, llvm_as, llvm_objdump, rustc}; + +fn main() { + llvm_as().input("ir.ll").run(); + rustc() + .input("main.rs") + .opt_level("3") + .lto("fat") + .linker_plugin_lto("on") + .link_arg("ir.bc") + .arg("-Zlinker-features=+lld") + .run(); + + llvm_objdump() + .input(dynamic_lib_name("main")) + .arg("--disassemble-symbols=rs_foo") + .run() + // The called function should be inlined. + // Check that we have a ret (to detect tail + // calls with a jmp) and no call. + .assert_stdout_contains("foo") + .assert_stdout_contains("ret") + .assert_stdout_not_contains("call"); +}