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
Joshua Nelson
parent
a959fee323
commit
0319b90a25
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@ -28,6 +28,12 @@ number of lines of LLVM IR across all instantiations of a generic function.
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Since most of the time compiling rustc is spent in LLVM, the idea is that by
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reducing the amount of code passed to LLVM, compiling rustc gets faster.
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To use `cargo-llvm-lines` together with somewhat custom rustc build process, you can use
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`-C save-temps` to obtain required LLVM IR. The option preserves temporary work products
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created during compilation. Among those is LLVM IR that represents an input to the
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optimization pipeline; ideal for our purposes. It is stored in files with `*.no-opt.bc`
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extension in LLVM bitcode format.
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Example usage:
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```
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cargo install cargo-llvm-lines
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@ -35,36 +41,44 @@ cargo install cargo-llvm-lines
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# Do a clean before every run, to not mix in the results from previous runs.
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./x.py clean
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RUSTFLAGS="--emit=llvm-ir" ./x.py build --stage 0 compiler/rustc
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env RUSTFLAGS=-Csave-temps ./x.py build --stage 0 compiler/rustc
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# Single crate, eg. rustc_middle
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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
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# Specify all crates of the compiler. (Relies on the glob support of your shell.)
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cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/debug/deps/*.ll > llvm-lines.txt
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# Single crate, e.g., rustc_middle. (Relies on the glob support of your shell.)
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# Convert unoptimized LLVM bitcode into a human readable LLVM assembly accepted by cargo-llvm-lines.
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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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./build/x86_64-unknown-linux-gnu/llvm/bin/llvm-dis "$f"
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done
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cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/rustc_middle-*.ll > llvm-lines-middle.txt
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# Specify all crates of the compiler.
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for f in build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/*.no-opt.bc; do
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./build/x86_64-unknown-linux-gnu/llvm/bin/llvm-dis "$f"
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done
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cargo llvm-lines --files ./build/x86_64-unknown-linux-gnu/stage0-rustc/x86_64-unknown-linux-gnu/release/deps/*.ll > llvm-lines.txt
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```
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Example output:
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Example output for the compiler:
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```
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Lines Copies Function name
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----- ------ -------------
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11802479 (100%) 52848 (100%) (TOTAL)
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1663902 (14.1%) 400 (0.8%) rustc_query_system::query::plumbing::get_query_impl::{{closure}}
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683526 (5.8%) 10579 (20.0%) core::ptr::drop_in_place
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568523 (4.8%) 528 (1.0%) rustc_query_system::query::plumbing::get_query_impl
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472715 (4.0%) 1134 (2.1%) hashbrown::raw::RawTable<T>::reserve_rehash
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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}}
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212800 (1.8%) 514 (1.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
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194813 (1.7%) 124 (0.2%) rustc_query_system::query::plumbing::force_query_impl
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158488 (1.3%) 1 (0.0%) rustc_middle::ty::query::<impl rustc_middle::ty::context::TyCtxt>::alloc_self_profile_query_strings
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119768 (1.0%) 418 (0.8%) core::ops::function::FnOnce::call_once
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119644 (1.0%) 1 (0.0%) rustc_target::spec::load_specific
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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}}
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81173 (0.7%) 1 (0.0%) rustc_middle::ty::query::stats::query_stats
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80306 (0.7%) 2029 (3.8%) core::ops::function::FnOnce::call_once{{vtable.shim}}
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78019 (0.7%) 1611 (3.0%) stacker::grow::{{closure}}
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69720 (0.6%) 3286 (6.2%) <&T as core::fmt::Debug>::fmt
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56327 (0.5%) 186 (0.4%) rustc_query_system::query::plumbing::incremental_verify_ich
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49714 (0.4%) 14 (0.0%) rustc_mir::dataflow::framework::graphviz::BlockFormatter<A>::write_node_label
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Lines Copies Function name
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----- ------ -------------
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45207720 (100%) 1583774 (100%) (TOTAL)
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2102350 (4.7%) 146650 (9.3%) core::ptr::drop_in_place
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615080 (1.4%) 8392 (0.5%) std::thread::local::LocalKey<T>::try_with
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594296 (1.3%) 1780 (0.1%) hashbrown::raw::RawTable<T>::rehash_in_place
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592071 (1.3%) 9691 (0.6%) core::option::Option<T>::map
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528172 (1.2%) 5741 (0.4%) core::alloc::layout::Layout::array
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466854 (1.0%) 8863 (0.6%) core::ptr::swap_nonoverlapping_one
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412736 (0.9%) 1780 (0.1%) hashbrown::raw::RawTable<T>::resize
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367776 (0.8%) 2554 (0.2%) alloc::raw_vec::RawVec<T,A>::grow_amortized
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367507 (0.8%) 643 (0.0%) rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
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355882 (0.8%) 6332 (0.4%) alloc::alloc::box_free
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354556 (0.8%) 14213 (0.9%) core::ptr::write
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354361 (0.8%) 3590 (0.2%) core::iter::traits::iterator::Iterator::fold
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347761 (0.8%) 3873 (0.2%) rustc_middle::ty::context::tls::set_tlv
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337534 (0.7%) 2377 (0.2%) alloc::raw_vec::RawVec<T,A>::allocate_in
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331690 (0.7%) 3192 (0.2%) hashbrown::raw::RawTable<T>::find
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328756 (0.7%) 3978 (0.3%) rustc_middle::ty::context::tls::with_context_opt
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326903 (0.7%) 642 (0.0%) rustc_query_system::query::plumbing::try_execute_query
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```
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Since this doesn't seem to work with incremental compilation or `x.py check`,
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