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codegen-units=1 + LTO causes 3-5% performance regression for sequential code

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#148670 In rust-lang/rust;

· naoNao89 opened on Nov 7, 2025

Unable to link code containing naked functions on ARM64 macOS with ThinLTO enabled

A-linkageArea: linking into static, shared libraries and binariesArea: linking into static, shared libraries and binaries

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

A-nakedArea: `#[naked]`, prologue and epilogue-free, functions, https://git.io/vAzzSArea: `#[naked]`, prologue and epilogue-free, functions, https://git.io/vAzzS

C-bugCategory: This is a bug.Category: This is a bug.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

Status: Open.

#148307 In rust-lang/rust;

· mkaput opened on Oct 30, 2025

linker error when building rustc with clang+lld 21 and <code>-C linker-plugin-lto</code>

A-linkageArea: linking into static, shared libraries and binariesArea: linking into static, shared libraries and binaries

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

T-bootstrapRelevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap)Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap)

Status: Open.

#147902 In rust-lang/rust;

· vadorovsky opened on Oct 20, 2025

Compiler Requested Report

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️

O-windowsOperating system: WindowsOperating system: Windows

S-needs-infoStatus: The issue lacks details necessary to triage or act on it.Status: The issue lacks details necessary to triage or act on it.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#147203 In rust-lang/rust;

· AllProAi opened on Sep 30, 2025

4000% performance regression with "-C target-cpu=x86-64-v3" and fat LTO

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

Status: Open.

#146497 In rust-lang/rust;

· im-0 opened on Sep 13, 2025

Rust LLVMIR causes errors after LTO on x86-32

A-ABIArea: Concerning the application binary interface (ABI)Area: Concerning the application binary interface (ABI)

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

O-x86_32Target: x86 processors, 32 bit (like i686-*) (also known as IA-32, i386, i586, i686)Target: x86 processors, 32 bit (like i686-*) (also known as IA-32, i386, i586, i686)

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#143818 In rust-lang/rust;

· jrmuizel opened on Jul 11, 2025

rustc SIGSEGV on RISC-V when compiling serde and other crates (stack overflow on 4 GB stack)

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

I-crashIssue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.Issue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.

O-riscvTarget: RISC-V architectureTarget: RISC-V architecture

Status: Open.

#143749 In rust-lang/rust;

· planetryan opened on Jul 10, 2025

Code model other than medium does not work with lto on riscv64

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

O-riscvTarget: RISC-V architectureTarget: RISC-V architecture

P-lowLow priorityLow priority

regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.Performance or correctness regression from one stable version to another.

S-has-mcveStatus: A Minimal Complete and Verifiable Example has been found for this issueStatus: A Minimal Complete and Verifiable Example has been found for this issue

Status: Open.

#139479 In rust-lang/rust;

· kxxt opened on Apr 7, 2025

Failure to link rust dependency with LTO-enabled C FFI code built with GCC

A-FFIArea: Foreign function interface (FFI)Area: Foreign function interface (FFI)

A-linkageArea: linking into static, shared libraries and binariesArea: linking into static, shared libraries and binaries

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#138681 In rust-lang/rust;

· glandium opened on Mar 19, 2025

<code>--emit obj</code> with <code>--crate-type staticlib</code> doesn't work when <code>-C lto=thin</code> is set

A-CLIArea: Command-line interface (CLI) to the compilerArea: Command-line interface (CLI) to the compiler

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#134998 In rust-lang/rust;

· ChrisDenton opened on Jan 1, 2025

Adding <code>lto = true</code> causes duplicated symbol errors on <code>.weak</code> symbols

A-inline-assemblyArea: Inline assembly (`asm!(…)`)Area: Inline assembly (`asm!(…)`)

A-linkageArea: linking into static, shared libraries and binariesArea: linking into static, shared libraries and binaries

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#133974 In rust-lang/rust;

· rslawson opened on Dec 6, 2024

Rustc fails to compile a program with ThinLTO and split-debuginfo = "packed"

A-codegenArea: Code generationArea: Code generation

A-debuginfoArea: Debugging information in compiled programs (DWARF, PDB, etc.)Area: Debugging information in compiled programs (DWARF, PDB, etc.)

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#132677 In rust-lang/rust;

· zamazan4ik opened on Nov 6, 2024