Investigate memory usage of compiling the packed_simd crate

[hsivonen]

Steps to reproduce

1. Create a new crate with cargo.
2. Add packed_simd = '0.3.1' to Cargo.toml of the new crate.
3. Build the new crate.

Actual results

While compiling packed_simd, rustc takes more than 2 GB of RAM.

Expected results

Lesser RAM usage.

Additional info

Maybe it's just the nature of packed_simd that it takes a lot of RAM to compile, and there's no bug. However, if RAM usage reached 3 GB in the future, the crate would become unbuildable on 32-bit systems. It might be worthwhile to investigate if building packed_simd has to take this much RAM or if there is an opportunity to use less RAM without adversely affecting compilation speed on systems that have plenty of RAM.

[gnzlbg]

cc @mw @nnethercote

[matthiaskrgr]

Looks like nll needs a lot of memory here

�[0m�[0m�[1m�[32m   Compiling�[0m packed_simd v0.3.1
  time: 0.054; rss: 57MB	parsing
  time: 0.000; rss: 58MB	attributes injection
  time: 0.000; rss: 58MB	recursion limit
  time: 0.000; rss: 58MB	crate injection
  time: 0.000; rss: 58MB	plugin loading
  time: 0.000; rss: 58MB	plugin registration
  time: 0.005; rss: 58MB	pre ast expansion lint checks
    time: 2.550; rss: 369MB	expand crate
    time: 0.000; rss: 369MB	check unused macros
  time: 2.550; rss: 369MB	expansion
  time: 0.000; rss: 369MB	maybe building test harness
  time: 0.012; rss: 369MB	maybe creating a macro crate
  time: 0.048; rss: 370MB	creating allocators
  time: 0.036; rss: 370MB	AST validation
  time: 0.497; rss: 412MB	name resolution
  time: 0.075; rss: 412MB	complete gated feature checking
  time: 0.321; rss: 481MB	lowering ast -> hir
  time: 0.081; rss: 482MB	early lint checks
    time: 0.052; rss: 504MB	validate hir map
  time: 0.353; rss: 504MB	indexing hir
  time: 0.000; rss: 504MB	load query result cache
  time: 0.000; rss: 504MB	looking for entry point
  time: 0.000; rss: 504MB	dep graph tcx init
  time: 0.001; rss: 504MB	looking for plugin registrar
  time: 0.001; rss: 504MB	looking for derive registrar
  time: 0.019; rss: 504MB	loop checking
  time: 0.024; rss: 504MB	attribute checking
    time: 0.000; rss: 515MB	solve_nll_region_constraints(DefId(0/1:2171 ~ packed_simd[a932]::v64[0]::f32x2[0]::{{constant}}[0]))
*snip*
    time: 0.000; rss: 527MB	solve_nll_region_constraints(DefId(0/1:4611 ~ packed_simd[a932]::vSize[0]::{{impl}}[587]::from[0]::U[0]::array[0]::{{constant}}[0]))
  time: 0.636; rss: 527MB	stability checking
  time: 0.124; rss: 527MB	type collecting
  time: 0.003; rss: 527MB	outlives testing
  time: 0.019; rss: 527MB	impl wf inference
    time: 0.000; rss: 1113MB	solve_nll_region_constraints(DefId(0/1:224 ~ packed_simd[a932]::codegen[0]::shuffle[0]::{{impl}}[0]::{{constant}}[0]))
*snip*
    time: 0.000; rss: 1246MB	solve_nll_region_constraints(DefId(0/1:4867 ~ packed_simd[a932]::vPtr[0]::{{impl}}[104]::{{constant}}[0]))
  time: 9.972; rss: 1408MB	coherence checking
  time: 0.002; rss: 1408MB	variance testing
    time: 0.000; rss: 1605MB	solve_nll_region_constraints(DefId(0/1:366 ~ packed_simd[a932]::codegen[0]::v16[0]::{{impl}}[0]::NT[0]::{{constant}}[0]))
*snip*
    time: 0.000; rss: 2013MB	solve_nll_region_constraints(DefId(0/0:4027 ~ packed_simd[a932]::codegen[0]::reductions[0]::mask[0]::{{impl}}[7]::any[0]))
    time: 0.000; rss: 2013MB	solve_nll_region_constraints(DefId(0/0:4053 ~ packed_simd[a932]::codegen[0]::reductions[0]::mask[0]::{{impl}}[17]::any[0]))
  time: 5.040; rss: 2013MB	MIR borrow checking
  time: 0.000; rss: 2013MB	dumping chalk-like clauses
  time: 0.005; rss: 2013MB	MIR effect checking
  time: 0.072; rss: 2018MB	death checking
  time: 0.021; rss: 2018MB	unused lib feature checking
  time: 0.176; rss: 2019MB	lint checking
  time: 0.000; rss: 2019MB	resolving dependency formats
    time: 0.890; rss: 2055MB	write metadata
      time: 0.010; rss: 2055MB	collecting roots
      time: 0.186; rss: 2056MB	collecting mono items
    time: 0.196; rss: 2056MB	monomorphization collection
    time: 0.001; rss: 2056MB	codegen unit partitioning
    time: 0.122; rss: 2060MB	codegen to LLVM IR
    time: 0.000; rss: 2060MB	assert dep graph
    time: 0.000; rss: 2060MB	serialize dep graph
  time: 1.215; rss: 2060MB	codegen
    time: 0.056; rss: 2063MB	llvm function passes [packed_simd.smey8184-cgu.0]
    time: 0.777; rss: 2071MB	llvm module passes [packed_simd.smey8184-cgu.0]
    time: 0.798; rss: 2079MB	codegen passes [packed_simd.smey8184-cgu.0]
  time: 1.703; rss: 1539MB	LLVM passes
  time: 0.000; rss: 1540MB	serialize work products
  time: 0.017; rss: 1540MB	linking

[gnzlbg]

Coherence checking also takes a good chunk of memory:

time: 0.000; rss: 1246MB	solve_nll_region_constraints(DefId(0/1:4867 ~ packed_simd[a932]::vPtr[0]::{{impl}}[104]::{{constant}}[0]))
  time: 9.972; rss: 1408MB	coherence checking

although NLL is the first suspect here. I wonder why NLL uses this much memory, packed_simd is full of methods, but the great majority of them are essentially one liners.

[memoryruins]

Reported the following spike of memory usage in #57432, which occurred after #56723

[mati865]

This one could be closed as duplicate of #57432 I guess.

[gnzlbg]

EDIT: @mati865 you are right, these are duplicates, I thought that was a different issue that apparently never got filled, so forget this.

---

original comment:

@mati865 while they are related, they are two different issues:

• this issue is about compiling packed_simd itself, which started using much more memory recently, resulting in some builds failing for consumers (encoding-rs)

• Compile time perf regression for packed-simd's max-rss #57432 is about increased compile-times and memory usage when compiling other crates when packed_simd is part of libcore (e.g. via core::simd)

[nnethercote]

I did a DHAT run. The "At t-gmax" measurement is the relevant one, it's short for "time of global max". It shows that the interning of constants within TypeFolder is accounting for over 54% of the global peak:

AP 1.1.1.1.1/2 (2 children) {
  Total:     912,261,120 bytes (12.02%, 7,312.63/Minstr) in 6 blocks (0%, 0/Minstr), avg size 152,043,520 bytes, avg lifetime 103,155,024,513.33 instrs (82.69% of program duration)
  At t-gmax: 912,261,120 bytes (54.74%) in 6 blocks (0%), avg size 152,043,520 bytes
  At t-end:  0 bytes (0%) in 0 blocks (0%), avg size 0 bytes
  Reads:     1,827,458,569 bytes (4.97%, 14,648.81/Minstr), 2/byte
  Writes:    844,260,160 bytes (9.59%, 6,767.54/Minstr), 0.93/byte
  Allocated at {
    #1: 0xB66BCCB: alloc (alloc.rs:72)
    #2: 0xB66BCCB: alloc (alloc.rs:148)
    #3: 0xB66BCCB: allocate_in<u8,alloc::alloc::Global> (raw_vec.rs:96)
    #4: 0xB66BCCB: with_capacity<u8> (raw_vec.rs:140)
    #5: 0xB66BCCB: new<u8> (lib.rs:66)
    #6: 0xB66BCCB: arena::DroplessArena::grow (lib.rs:346)
    #7: 0x8C1BB25: alloc_raw (lib.rs:362)
    #8: 0x8C1BB25: alloc<rustc::ty::sty::LazyConst> (lib.rs:378)
    #9: 0x8C1BB25: alloc<rustc::ty::sty::LazyConst> (lib.rs:465)
    #10: 0x8C1BB25: intern_lazy_const (context.rs:1123)
    #11: 0x8C1BB25: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_const (project.rs:423)
    #12: 0x8C1B235: fold_with<rustc::traits::project::AssociatedTypeNormalizer> (structural_impls.rs:1049)
    #13: 0x8C1B235: super_fold_with<rustc::traits::project::AssociatedTypeNormalizer> (structural_impls.rs:719)
    #14: 0x8C1B235: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty (project.rs:337)
    #15: 0x890C0D0: fold_with<rustc::traits::project::AssociatedTypeNormalizer> (structural_impls.rs:769)
    #16: 0x890C0D0: super_fold_with<rustc::traits::project::AssociatedTypeNormalizer> (subst.rs:135)
    #17: 0x890C0D0: fold_with<rustc::ty::subst::Kind,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #18: 0x890C0D0: {{closure}}<rustc::traits::project::AssociatedTypeNormalizer> (subst.rs:328)
    #19: 0x890C0D0: call_once<(&rustc::ty::subst::Kind),closure> (function.rs:279)
    #20: 0x890C0D0: map<&rustc::ty::subst::Kind,rustc::ty::subst::Kind,&mut closure> (option.rs:414)
    #21: 0x890C0D0: next<rustc::ty::subst::Kind,core::slice::Iter<rustc::ty::subst::Kind>,closure> (mod.rs:567)
    #22: 0x890C0D0: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend (lib.rs:1349)
    #23: 0x8EF9787: from_iter<[rustc::ty::subst::Kind; 8],core::iter::adapters::Map<core::slice::Iter<rustc::ty::subst::Kind>, closure>> (lib.rs:1333)
    #24: 0x8EF9787: collect<core::iter::adapters::Map<core::slice::Iter<rustc::ty::subst::Kind>, closure>,smallvec::SmallVec<[rustc::ty::subst::Kind; 8]>> (iterator.rs:1466)
    #25: 0x8EF9787: rustc::ty::subst::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::List<rustc::ty::subst::Kind<'tcx>>>::super_fold_with (subst.rs:328)
    #26: 0x8C1B183: fold_with<&rustc::ty::List<rustc::ty::subst::Kind>,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #27: 0x8C1B183: super_fold_with<rustc::traits::project::AssociatedTypeNormalizer> (structural_impls.rs:721)
    #28: 0x8C1B183: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty (project.rs:337)
    #29: 0x890C0D0: fold_with<rustc::traits::project::AssociatedTypeNormalizer> (structural_impls.rs:769)
    #30: 0x890C0D0: super_fold_with<rustc::traits::project::AssociatedTypeNormalizer> (subst.rs:135)
    #31: 0x890C0D0: fold_with<rustc::ty::subst::Kind,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #32: 0x890C0D0: {{closure}}<rustc::traits::project::AssociatedTypeNormalizer> (subst.rs:328)
    #33: 0x890C0D0: call_once<(&rustc::ty::subst::Kind),closure> (function.rs:279)
    #34: 0x890C0D0: map<&rustc::ty::subst::Kind,rustc::ty::subst::Kind,&mut closure> (option.rs:414)
    #35: 0x890C0D0: next<rustc::ty::subst::Kind,core::slice::Iter<rustc::ty::subst::Kind>,closure> (mod.rs:567)
    #36: 0x890C0D0: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend (lib.rs:1349)
    #37: 0x8EF9787: from_iter<[rustc::ty::subst::Kind; 8],core::iter::adapters::Map<core::slice::Iter<rustc::ty::subst::Kind>, closure>> (lib.rs:1333)
    #38: 0x8EF9787: collect<core::iter::adapters::Map<core::slice::Iter<rustc::ty::subst::Kind>, closure>,smallvec::SmallVec<[rustc::ty::subst::Kind; 8]>> (iterator.rs:1466)
    #39: 0x8EF9787: rustc::ty::subst::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::List<rustc::ty::subst::Kind<'tcx>>>::super_fold_with (subst.rs:328)
    #40: 0x8BFE173: fold_with<&rustc::ty::List<rustc::ty::subst::Kind>,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #41: 0x8BFE173: super_fold_with<rustc::traits::project::AssociatedTypeNormalizer> (macros.rs:344)
    #42: 0x8BFE173: fold_with<rustc::ty::sty::TraitRef,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #43: 0x8BFE173: super_fold_with<rustc::ty::sty::TraitRef,rustc::traits::project::AssociatedTypeNormalizer> (macros.rs:397)
    #44: 0x8BFE173: fold_with<core::option::Option<rustc::ty::sty::TraitRef>,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #45: 0x8BFE173: super_fold_with<rustc::traits::project::AssociatedTypeNormalizer> (macros.rs:344)
    #46: 0x8BFE173: fold_with<rustc::ty::ImplHeader,rustc::traits::project::AssociatedTypeNormalizer> (fold.rs:47)
    #47: 0x8BFE173: fold<rustc::ty::ImplHeader> (project.rs:315)
    #48: 0x8BFE173: normalize_with_depth<rustc::ty::ImplHeader> (project.rs:274)
    #49: 0x8BFE173: normalize<rustc::ty::ImplHeader> (project.rs:258)
    #50: 0x8BFE173: rustc::traits::coherence::with_fresh_ty_vars (coherence.rs:107)

[nnethercote]

@eddby @oli-obk @RalfJung Any thoughts on how to improve intern_lazy_const?

[RalfJung]

Cc @eddyb

[nnethercote]

Any thoughts on how to improve intern_lazy_const?

There is an obvious problem: intern_lazy_const doesn't intern the value! And the values passed are exceedingly repetitive. Here's a histogram of the top 10, which account for 97.2% of the calls:

17886042 counts:
(  1)  5253160 (29.4%, 29.4%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 2 }) })
(  2)  5192895 (29.0%, 58.4%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 4 }) })
(  3)  3928986 (22.0%, 80.4%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 8 }) })
(  4)  1600916 ( 9.0%, 89.3%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 16 }) })
(  5)   719785 ( 4.0%, 93.3%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 32 }) })
(  6)   299507 ( 1.7%, 95.0%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 1 }) })
(  7)   271847 ( 1.5%, 96.5%): Evaluated(Const { ty: usize, val: Scalar(Bits { size: 8, bits: 64 }) })
(  8)    61636 ( 0.3%, 96.9%): Unevaluated(DefId(0/1:4735 ~ packed_simd[3c0f]::vPtr[0]::mptrx4[0]::{{constant}}[0]), [])
(  9)    61636 ( 0.3%, 97.2%): Unevaluated(DefId(0/1:4823 ~ packed_simd[3c0f]::vPtr[0]::mptrx8[0]::{{constant}}[0]), [])
( 10)    61636 ( 0.3%, 97.6%): Unevaluated(DefId(0/1:4653 ~ packed_simd[3c0f]::vPtr[0]::mptrx2[0]::{{constant}}[0]), [])

Fixing this should drastically reduce the memory usage.

I tried doing the obvious thing by introducing GlobalCtxt::lazy_const_interner, heavily inspired by GlobalCtxt::layout_interner, but I couldn't get the lifetimes to work. I will try again tomorrow if nobody else beats me to it.