How are LLVM-IR passes done in Rust?

bexxmodd · November 3, 2021, 12:07am

Hello,

I recently got introduced to the LLVM-IR and implemented a couple of sanitizers myself using its C++ API. I know that Rust's compiler is built using LLVM infrastructure and it does several passes as well. My question is: as LLVM IR doesn't have Rust API how does the Rust compiler handles optimizations, and does Passes? Does it use C++ code to do that or there is a Rust binding for it? Crates I found for binding are somewhat personal projects?! I don't think Rust's compiler is built using those crates.

Or Rust doesn't use LLVM IR and it does something else to optimize code and do sanitization etc.?

sanxiyn · November 3, 2021, 12:16am

rustc has its own internal Rust binding for LLVM. It is not published as a crate and while it is (necessarily) battle tested, it probably is not reusable at all outside rustc. Here it is:

github.com

rust-lang/rust/blob/master/compiler/rustc_codegen_llvm/src/llvm/ffi.rs

#![allow(non_camel_case_types)]
#![allow(non_upper_case_globals)]

use rustc_codegen_ssa::coverageinfo::map as coverage_map;

use super::debuginfo::{
    DIArray, DIBasicType, DIBuilder, DICompositeType, DIDerivedType, DIDescriptor, DIEnumerator,
    DIFile, DIFlags, DIGlobalVariableExpression, DILexicalBlock, DILocation, DINameSpace,
    DISPFlags, DIScope, DISubprogram, DISubrange, DITemplateTypeParameter, DIType, DIVariable,
    DebugEmissionKind,
};

use libc::{c_char, c_int, c_uint, size_t};
use libc::{c_ulonglong, c_void};

use std::marker::PhantomData;

use super::RustString;

pub type Bool = c_uint;

This file has been truncated. show original

bexxmodd · November 3, 2021, 12:22am

Oh, ok so it does use Rust binding for LLVM IR C++ API? For example, if I want to try and implement a custom pass I can't reuse that piece separately?

Michael-F-Bryan · November 3, 2021, 12:42am

You would need to modify that part of the compiler to implement your own pass. Probably somewhere near this function.

system · February 1, 2022, 12:42am

This topic was automatically closed 90 days after the last reply. We invite you to open a new topic if you have further questions or comments.