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Ensure fat LTO doesn't merge everything into the allocator module

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bjorn3
2025-09-05 19:09:39 +00:00
parent 9239d141dc
commit 2cf94b92ca
4 changed files with 21 additions and 3 deletions
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8
compiler/rustc_codegen_llvm/src/back/lto.rs
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@@ -11,7 +11,7 @@ use object::{Object, ObjectSection};
use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule, ThinShared};
use rustc_codegen_ssa::back::write::{CodegenContext, FatLtoInput};
use rustc_codegen_ssa::traits::*;
use rustc_codegen_ssa::{ModuleCodegen, looks_like_rust_object_file};
use rustc_codegen_ssa::{ModuleCodegen, ModuleKind, looks_like_rust_object_file};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::memmap::Mmap;
use rustc_errors::DiagCtxtHandle;
@@ -225,9 +225,15 @@ fn fat_lto(
// All the other modules will be serialized and reparsed into the new
// context, so this hopefully avoids serializing and parsing the largest
// codegen unit.
//
// Additionally use a regular module as the base here to ensure that various
// file copy operations in the backend work correctly. The only other kind
// of module here should be an allocator one, and if your crate is smaller
// than the allocator module then the size doesn't really matter anyway.
let costliest_module = in_memory
.iter()
.enumerate()
.filter(|&(_, module)| module.kind == ModuleKind::Regular)
.map(|(i, module)| {
let cost = unsafe { llvm::LLVMRustModuleCost(module.module_llvm.llmod()) };
(cost, i)