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rustc: Handle modules in "fat" LTO more robustly

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When performing a "fat" LTO the compiler has a whole mess of codegen
units that it links together. To do this it needs to select one module
as a "base" module and then link everything else into this module.
Previously LTO passes assume that there's at least one module in-memory
to link into, but nowadays that's not always true! With incremental
compilation modules may actually largely be cached and it may be
possible that there's no in-memory modules to work with.

This commit updates the logic of the LTO backend to handle modules a bit
more uniformly during a fat LTO. This commit immediately splits them
into two lists, one serialized and one in-memory. The in-memory list is
then searched for the largest module and failing that we simply
deserialize the first serialized module and link into that. This
refactoring avoids juggling three lists, two of which are serialized
modules and one of which is half serialized and half in-memory.

Closes #63349
This commit is contained in:
Alex Crichton 2019-08-27 12:25:35 -07:00
parent 0396aace27
commit 1a4330d2a2
5 changed files with 59 additions and 49 deletions
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7
src/librustc_codegen_llvm/lib.rs
View file

@ -54,6 +54,7 @@ use syntax_pos::symbol::InternedString;
pub use llvm_util::target_features;
use std::any::Any;
use std::sync::{mpsc, Arc};
use std::ffi::CStr;
use rustc::dep_graph::DepGraph;
use rustc::middle::cstore::{EncodedMetadata, MetadataLoader};
@ -386,13 +387,13 @@ impl ModuleLlvm {
fn parse(
cgcx: &CodegenContext<LlvmCodegenBackend>,
name: &str,
buffer: &back::lto::ModuleBuffer,
name: &CStr,
buffer: &[u8],
handler: &Handler,
) -> Result<Self, FatalError> {
unsafe {
let llcx = llvm::LLVMRustContextCreate(cgcx.fewer_names);
let llmod_raw = buffer.parse(name, llcx, handler)?;
let llmod_raw = back::lto::parse_module(llcx, name, buffer, handler)?;
let tm = match (cgcx.tm_factory.0)() {
Ok(m) => m,
Err(e) => {