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

The `--emit=llvm-ir` emits an optimized LLVM IR. For optimized builds it will be
highly inaccurate estimate of the amount IR generated initially.  While the
inaccuracy can be somewhat reduce after disabling the optimization, that in turn
has other unintended consequences, since opt-level controls the emission of
lifetime markers, sharing of generics between crates, instantiation of inline
functions, etc.

Use `-Csave-temps` and `no-opt` bitcode as a basis for more accurate estimate of
initial work handed of to the LLVM.
This commit is contained in:
Tomasz Miąsko 2021-03-05 00:00:00 +00:00 committed by Joshua Nelson
parent a959fee323
commit 0319b90a25
1 changed files with 40 additions and 26 deletions
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66
src/profiling.md
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@ -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 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. 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: Example usage:
``` ```
cargo install cargo-llvm-lines 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. # Do a clean before every run, to not mix in the results from previous runs.
./x.py clean ./x.py clean
RUSTFLAGS="--emit=llvm-ir" ./x.py build --stage 0 compiler/rustc env RUSTFLAGS=-Csave-temps ./x.py build --stage 0 compiler/rustc
# Single crate, eg. rustc_middle # Single crate, e.g., rustc_middle. (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/rustc_middle-a539a639bdab6513.ll > llvm-lines-middle.txt # Convert unoptimized LLVM bitcode into a human readable LLVM assembly accepted by cargo-llvm-lines.
# Specify all crates of the compiler. (Relies on the glob support of your shell.) for f in build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_middle-*.no-opt.bc; do
cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/debug/deps/*.ll > llvm-lines.txt ./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 Lines Copies Function name
----- ------ ------------- ----- ------ -------------
11802479 (100%) 52848 (100%) (TOTAL) 45207720 (100%) 1583774 (100%) (TOTAL)
1663902 (14.1%) 400 (0.8%) rustc_query_system::query::plumbing::get_query_impl::{{closure}} 2102350 (4.7%) 146650 (9.3%) core::ptr::drop_in_place
683526 (5.8%) 10579 (20.0%) core::ptr::drop_in_place 615080 (1.4%) 8392 (0.5%) std::thread::local::LocalKey<T>::try_with
568523 (4.8%) 528 (1.0%) rustc_query_system::query::plumbing::get_query_impl 594296 (1.3%) 1780 (0.1%) hashbrown::raw::RawTable<T>::rehash_in_place
472715 (4.0%) 1134 (2.1%) hashbrown::raw::RawTable<T>::reserve_rehash 592071 (1.3%) 9691 (0.6%) core::option::Option<T>::map
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}} 528172 (1.2%) 5741 (0.4%) core::alloc::layout::Layout::array
212800 (1.8%) 514 (1.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl 466854 (1.0%) 8863 (0.6%) core::ptr::swap_nonoverlapping_one
194813 (1.7%) 124 (0.2%) rustc_query_system::query::plumbing::force_query_impl 412736 (0.9%) 1780 (0.1%) hashbrown::raw::RawTable<T>::resize
158488 (1.3%) 1 (0.0%) rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::alloc_self_profile_query_strings 367776 (0.8%) 2554 (0.2%) alloc::raw_vec::RawVec<T,A>::grow_amortized
119768 (1.0%) 418 (0.8%) core::ops::function::FnOnce::call_once 367507 (0.8%) 643 (0.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
119644 (1.0%) 1 (0.0%) rustc_target::spec::load_specific 355882 (0.8%) 6332 (0.4%) alloc::alloc::box_free
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}} 354556 (0.8%) 14213 (0.9%) core::ptr::write
81173 (0.7%) 1 (0.0%) rustc_middle::ty::query::stats::query_stats 354361 (0.8%) 3590 (0.2%) core::iter::traits::iterator::Iterator::fold
80306 (0.7%) 2029 (3.8%) core::ops::function::FnOnce::call_once{{vtable.shim}} 347761 (0.8%) 3873 (0.2%) rustc_middle::ty::context::tls::set_tlv
78019 (0.7%) 1611 (3.0%) stacker::grow::{{closure}} 337534 (0.7%) 2377 (0.2%) alloc::raw_vec::RawVec<T,A>::allocate_in
69720 (0.6%) 3286 (6.2%) <&T as core::fmt::Debug>::fmt 331690 (0.7%) 3192 (0.2%) hashbrown::raw::RawTable<T>::find
56327 (0.5%) 186 (0.4%) rustc_query_system::query::plumbing::incremental_verify_ich 328756 (0.7%) 3978 (0.3%) rustc_middle::ty::context::tls::with_context_opt
49714 (0.4%) 14 (0.0%) rustc_mir::dataflow::framework::graphviz::BlockFormatter<A>::write_node_label 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`, Since this doesn't seem to work with incremental compilation or `x.py check`,