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incremental = true causes 4-5x build time regression in generated rustc build times #52374

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RalfJung opened this issue Jul 14, 2018 · 5 comments
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incremental = true causes 4-5x build time regression in generated rustc build times #52374

RalfJung opened this issue Jul 14, 2018 · 5 comments
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A-incr-comp Area: Incremental compilation WG-compiler-performance Working group: Compiler Performance WG-incr-comp Working group: Incremental compilation

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@RalfJung
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RalfJung commented Jul 14, 2018 •
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I am running rm build/*/stage* -rf && ./x.py build src/libstd in two different situations: With incremental = true and with incremental = false. All the other settings in config.toml are commented out. This is using 1731f0a.

With incremental = false, the build step "Building stage1 std artifacts" takes 46s.
With incremental = true, the same step takes 4m 46s.

These are compiled using the stage0 compiler artifacts -- seems like those become way slower when incremental build is enabled?

(I am currently doing this experiment again just to be sure.)
@oli-obk oli-obk added the WG-compiler-performance Working group: Compiler Performance label Jul 14, 2018
@oli-obk
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oli-obk commented Jul 14, 2018

cc @michaelwoerister

@oli-obk oli-obk added A-incr-comp Area: Incremental compilation WG-incr-comp Working group: Incremental compilation labels Jul 14, 2018
@RalfJung
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I have reproduced this. I also refined the command to rm build/*/stage* -rf && ./x.py build src/libstd --stage 1 to take less long. ;)

incremental = false:

Building stage1 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   Compiling cc v1.0.17
   Compiling core v0.0.0 (file:///home/r/src/rust/rustc/src/libcore)
   Compiling build_helper v0.1.0 (file:///home/r/src/rust/rustc/src/build_helper)
   Compiling unwind v0.0.0 (file:///home/r/src/rust/rustc/src/libunwind)
   Compiling compiler_builtins v0.0.0 (file:///home/r/src/rust/rustc/src/rustc/compiler_builtins_shim)
   Compiling cmake v0.1.31
   Compiling alloc_jemalloc v0.0.0 (file:///home/r/src/rust/rustc/src/liballoc_jemalloc)
   Compiling std v0.0.0 (file:///home/r/src/rust/rustc/src/libstd)
   Compiling rustc_msan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_msan)
   Compiling rustc_tsan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_tsan)
   Compiling rustc_lsan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_lsan)
   Compiling rustc_asan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_asan)
   Compiling libc v0.0.0 (file:///home/r/src/rust/rustc/src/rustc/libc_shim)
   Compiling alloc v0.0.0 (file:///home/r/src/rust/rustc/src/liballoc)
   Compiling std_unicode v0.0.0 (file:///home/r/src/rust/rustc/src/libstd_unicode)
   Compiling alloc_system v0.0.0 (file:///home/r/src/rust/rustc/src/liballoc_system)
   Compiling panic_abort v0.0.0 (file:///home/r/src/rust/rustc/src/libpanic_abort)
   Compiling panic_unwind v0.0.0 (file:///home/r/src/rust/rustc/src/libpanic_unwind)
    Finished release [optimized] target(s) in 48.04s

incremental = true:

Building stage1 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   Compiling cc v1.0.17
   Compiling core v0.0.0 (file:///home/r/src/rust/rustc/src/libcore)
   Compiling build_helper v0.1.0 (file:///home/r/src/rust/rustc/src/build_helper)
   Compiling unwind v0.0.0 (file:///home/r/src/rust/rustc/src/libunwind)
   Compiling compiler_builtins v0.0.0 (file:///home/r/src/rust/rustc/src/rustc/compiler_builtins_shim)
   Compiling cmake v0.1.31
   Compiling alloc_jemalloc v0.0.0 (file:///home/r/src/rust/rustc/src/liballoc_jemalloc)
   Compiling std v0.0.0 (file:///home/r/src/rust/rustc/src/libstd)
   Compiling rustc_asan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_asan)
   Compiling rustc_tsan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_tsan)
   Compiling rustc_lsan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_lsan)
   Compiling rustc_msan v0.0.0 (file:///home/r/src/rust/rustc/src/librustc_msan)
   Compiling libc v0.0.0 (file:///home/r/src/rust/rustc/src/rustc/libc_shim)
   Compiling alloc v0.0.0 (file:///home/r/src/rust/rustc/src/liballoc)
   Compiling std_unicode v0.0.0 (file:///home/r/src/rust/rustc/src/libstd_unicode)
   Compiling alloc_system v0.0.0 (file:///home/r/src/rust/rustc/src/liballoc_system)
   Compiling panic_abort v0.0.0 (file:///home/r/src/rust/rustc/src/libpanic_abort)
   Compiling panic_unwind v0.0.0 (file:///home/r/src/rust/rustc/src/libpanic_unwind)
    Finished release [optimized] target(s) in 4m 51s

@RalfJung
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RalfJung commented Jul 14, 2018 •
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This does not just affect libstd. If I can trust my backscroll here, a "stage1 compiler artifacts" build takes 25m 20s with incremental = true, whereas it just takes 8m 06s with incremental = false.

@RalfJung RalfJung changed the title incremental = true causes 5x build time regression for stage1 libstd incremental = true causes 5x build time regression in generated rustc build times Jul 14, 2018
@RalfJung RalfJung changed the title incremental = true causes 5x build time regression in generated rustc build times incremental = true causes 4-5x build time regression in generated rustc build times Jul 14, 2018
@michaelwoerister
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Yes, that's a known issue, unfortunately. #52309 will hopefully solve this in the medium term.

@alexcrichton
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With incremental ThinLTO now implemented, I think this is largely "fixed enough"

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A-incr-comp Area: Incremental compilation WG-compiler-performance Working group: Compiler Performance WG-incr-comp Working group: Incremental compilation
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