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Use more accurate estimate of generated LLVM IR with llvm-lines #1049

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Use more accurate estimate of generated LLVM IR with llvm-lines #1049

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68 changes: 41 additions & 27 deletions src/profiling.md
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Original file line number Diff line number Diff line change
Expand Up @@ -28,43 +28,57 @@ 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
# On a normal crate you could now run `cargo llvm-lines`, but x.py isn't normal :P

# 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.)
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Suggested change
# Single crate, e.g., rustc_middle. (Relies on the glob support of your shell.)
# 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
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Do you think this should mention that x86_64-unknown-linux-gnu varies based on the target? Or is it self-evident?

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I'd say it's easy enough to figure out what's wrong when you get file not found errors. Also bash syntax is used here, so unfortunately copy-pasting wouldn't work for windows anyway.

./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`,
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