diff --git a/src/profiling.md b/src/profiling.md
index 429376167..155dda97d 100644
--- a/src/profiling.md
+++ b/src/profiling.md
@@ -28,6 +28,12 @@ number of lines of LLVM IR across all instantiations of a generic function.
Since most of the time compiling rustc is spent in LLVM, the idea is that by
reducing the amount of code passed to LLVM, compiling rustc gets faster.
+To use `cargo-llvm-lines` together with somewhat custom rustc build process, you can use
+`-C save-temps` to obtain required LLVM IR. The option preserves temporary work products
+created during compilation. Among those is LLVM IR that represents an input to the
+optimization pipeline; ideal for our purposes. It is stored in files with `*.no-opt.bc`
+extension in LLVM bitcode format.
+
Example usage:
```
cargo install cargo-llvm-lines
@@ -35,36 +41,44 @@ cargo install cargo-llvm-lines
# Do a clean before every run, to not mix in the results from previous runs.
./x.py clean
-RUSTFLAGS="--emit=llvm-ir" ./x.py build --stage 0 compiler/rustc
-
-# Single crate, eg. rustc_middle
-cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/debug/deps/rustc_middle-a539a639bdab6513.ll > llvm-lines-middle.txt
-# Specify all crates of the compiler. (Relies on the glob support of your shell.)
-cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/debug/deps/*.ll > llvm-lines.txt
+env RUSTFLAGS=-Csave-temps ./x.py build --stage 0 compiler/rustc
+
+# Single crate, e.g., rustc_middle. (Relies on the glob support of your shell.)
+# Convert unoptimized LLVM bitcode into a human readable LLVM assembly accepted by cargo-llvm-lines.
+for f in build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_middle-*.no-opt.bc; do
+ ./build/x86_64-unknown-linux-gnu/llvm/bin/llvm-dis "$f"
+done
+cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_middle-*.ll > llvm-lines-middle.txt
+
+# Specify all crates of the compiler.
+for f in build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/*.no-opt.bc; do
+ ./build/x86_64-unknown-linux-gnu/llvm/bin/llvm-dis "$f"
+done
+cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/*.ll > llvm-lines.txt
```
-Example output:
+Example output for the compiler:
```
- Lines Copies Function name
- ----- ------ -------------
- 11802479 (100%) 52848 (100%) (TOTAL)
- 1663902 (14.1%) 400 (0.8%) rustc_query_system::query::plumbing::get_query_impl::{{closure}}
- 683526 (5.8%) 10579 (20.0%) core::ptr::drop_in_place
- 568523 (4.8%) 528 (1.0%) rustc_query_system::query::plumbing::get_query_impl
- 472715 (4.0%) 1134 (2.1%) hashbrown::raw::RawTable<T>::reserve_rehash
- 306782 (2.6%) 1320 (2.5%) rustc_middle::ty::query::plumbing::<impl rustc_query_system::query::QueryContext for rustc_middle::ty::context::TyCtxt>::start_query::{{closure}}::{{closure}}::{{closure}}
- 212800 (1.8%) 514 (1.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
- 194813 (1.7%) 124 (0.2%) rustc_query_system::query::plumbing::force_query_impl
- 158488 (1.3%) 1 (0.0%) rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::alloc_self_profile_query_strings
- 119768 (1.0%) 418 (0.8%) core::ops::function::FnOnce::call_once
- 119644 (1.0%) 1 (0.0%) rustc_target::spec::load_specific
- 104153 (0.9%) 7 (0.0%) rustc_middle::ty::context::_DERIVE_rustc_serialize_Decodable_D_FOR_TypeckResults::<impl rustc_serialize::serialize::Decodable<__D> for rustc_middle::ty::context::TypeckResults>::decode::{{closure}}
- 81173 (0.7%) 1 (0.0%) rustc_middle::ty::query::stats::query_stats
- 80306 (0.7%) 2029 (3.8%) core::ops::function::FnOnce::call_once{{vtable.shim}}
- 78019 (0.7%) 1611 (3.0%) stacker::grow::{{closure}}
- 69720 (0.6%) 3286 (6.2%) <&T as core::fmt::Debug>::fmt
- 56327 (0.5%) 186 (0.4%) rustc_query_system::query::plumbing::incremental_verify_ich
- 49714 (0.4%) 14 (0.0%) rustc_mir::dataflow::framework::graphviz::BlockFormatter<A>::write_node_label
+ Lines Copies Function name
+ ----- ------ -------------
+ 45207720 (100%) 1583774 (100%) (TOTAL)
+ 2102350 (4.7%) 146650 (9.3%) core::ptr::drop_in_place
+ 615080 (1.4%) 8392 (0.5%) std::thread::local::LocalKey<T>::try_with
+ 594296 (1.3%) 1780 (0.1%) hashbrown::raw::RawTable<T>::rehash_in_place
+ 592071 (1.3%) 9691 (0.6%) core::option::Option<T>::map
+ 528172 (1.2%) 5741 (0.4%) core::alloc::layout::Layout::array
+ 466854 (1.0%) 8863 (0.6%) core::ptr::swap_nonoverlapping_one
+ 412736 (0.9%) 1780 (0.1%) hashbrown::raw::RawTable<T>::resize
+ 367776 (0.8%) 2554 (0.2%) alloc::raw_vec::RawVec<T,A>::grow_amortized
+ 367507 (0.8%) 643 (0.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
+ 355882 (0.8%) 6332 (0.4%) alloc::alloc::box_free
+ 354556 (0.8%) 14213 (0.9%) core::ptr::write
+ 354361 (0.8%) 3590 (0.2%) core::iter::traits::iterator::Iterator::fold
+ 347761 (0.8%) 3873 (0.2%) rustc_middle::ty::context::tls::set_tlv
+ 337534 (0.7%) 2377 (0.2%) alloc::raw_vec::RawVec<T,A>::allocate_in
+ 331690 (0.7%) 3192 (0.2%) hashbrown::raw::RawTable<T>::find
+ 328756 (0.7%) 3978 (0.3%) rustc_middle::ty::context::tls::with_context_opt
+ 326903 (0.7%) 642 (0.0%) rustc_query_system::query::plumbing::try_execute_query
```
Since this doesn't seem to work with incremental compilation or `x.py check`,