Brenhin Keller (Jul 22 2022 at 18:03): Brenhin Keller (Jul 22 2022 at 18:03):Is there a way to tell constant propagation to just keep propagating? I keep running into cases where the types are perfectly well known, but constant propagation has been "Disabled by argument and rettype heuristics" and the return type has been widened into something else.
Brenhin Keller (Jul 22 2022 at 18:03):At first glance it seems like Base.@constprop :aggressive should do exactly what I want, but so far when I've tried it it actually hasn't helped
Zachary P Christensen (Jul 22 2022 at 18:14):I haven't found it terribly useful in practice (similar experiences). I would be happy to help but I can't promise that I'm smart enough to figure it out.
Brenhin Keller (Jul 22 2022 at 18:16):The next thing I'm trying is just adding manual type annotations.. think that'll work?
Brenhin Keller (Jul 22 2022 at 18:17):The context is the top-level functions in https://github.com/brenhinkeller/StaticMPI.jl
Brenhin Keller (Jul 22 2022 at 18:19):I'm trying to get things to statically compile, so need total type stability -- which so far works fine if I keep the whole program _super simple_ -- but as soon as I try to do something less trivial, functions that were previously inferring stably start giving that "Disabled by argument and rettype heuristics" message in Cthulhu and I start getting Union{}
Zachary P Christensen (Jul 22 2022 at 18:20):is it the source, dest, and tag in the MPI_* methods?
Brenhin Keller (Jul 22 2022 at 18:27):The return types of functions like https://github.com/brenhinkeller/StaticMPI.jl/blob/main/src/StaticMPI.jl#L110-L118 have been giving me a lot of trouble -- like I'll put an Int32 in the ref, but when I fetch it back out it doesn't seem to know the type any more unless I annotate it
Brenhin Keller (Jul 22 2022 at 18:28):The very simplest functions are fine, so like this example in the tests works just fine: https://github.com/brenhinkeller/StaticMPI.jl/blob/main/test/scripts/mpihello_mpich.jl
Brenhin Keller (Jul 22 2022 at 18:28):But the Isend and Irecv have been a lot of trouble to get working
Brenhin Keller (Jul 22 2022 at 18:37):This is my current attempt which I just can't get to work
https://github.com/brenhinkeller/StaticMPI.jl/blob/main/test/scripts/mpisendrecv.jl
(though there may also be some regular old bugs in there confounding things -- it doesn't help that I can't call any of these MPI functions interactively to test things because they segfault unless compiled in a way that links to libmpi :laughing: )
Fredrik Ekre (Jul 22 2022 at 18:48):What happens if you use the concrete type RefValue{T} instead of the abstract type Ref{T}?
Brenhin Keller (Jul 22 2022 at 18:49):Hmm, good point..
Zachary P Christensen (Jul 22 2022 at 18:54):RefValue was my gonna be my first guess too. Perhaps going back and forth betweenRef and ⅋ into a pointer is part of the problem. I'm not sure how well the heuristics of constant propagation play with memory storage.
Brenhin Keller (Jul 22 2022 at 19:13):Yeah, that probably doesn't help..
chriselrod (Jul 23 2022 at 04:13):BTW, note that Julia 1.8 adds the effects system, and Cthulhu can help you inspect inferred effects (e for effects).
chriselrod (Jul 23 2022 at 04:18):It helps to turn off optimizations o, otherwise a lot of the interesting code will be compiled away.
chriselrod (Jul 23 2022 at 04:18):These allow constant evaluation, which is dramatically faster than constant propagation. E.g., constant propagation for sin(1.0) means running code through the AbstractInterpreter, which is a very slow interpreter, while constant evaluation means the compiler just gets to call sin(::Float64), so it's likely to be more aggressive.
But RefValues do cause problems currently, because of course setfield! has a side effect, and getfield of a memory address isn't consistent
[(!c,!e,+n,+t,+s)]reftest()
@ Main REPL[5]:1
Variables
#self#::Core.Const(reftest)
x::Base.RefValue{Int64}
│ ─ %-1 = invoke reftest()::Int64
@ REPL[5]:2 within `reftest`
1 ─ %1 = Base.RefValue::Core.Const(Base.RefValue)
│ %2 = Core.apply_type(%1, Main.Int)::Core.Const(Base.RefValue{Int64})
│ (x = (%2)())::Base.RefValue{Int64}
│ @ REPL[5]:3 within `reftest`
│ Base.setindex!(x, 3)::Any
│ @ REPL[5]:4 within `reftest`
│ %5 = Base.getindex(x)::Int64
└── return %5
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• (?c,+e,+n,+t,+s) %3 = RefValue()::Base.RefValue{Int64}
(!c,!e,+n,+t,+s) %4 = < constprop > setindex!(::Base.RefValue{Int64},::Core.Const(3))::Any
(!c,+e,+n,+t,+s) %5 = getindex(::Base.RefValue{Int64})::Int64
Some sort of lifetime modeling could handle this in the future.
chriselrod (Jul 23 2022 at 04:20):Folks in Boston were treated to an excellent presentation by @Shuhei Kadowaki on Thursday.
Brenhin Keller (Jul 23 2022 at 04:21):Oh cool!
Brenhin Keller (Jul 23 2022 at 04:23):Success! https://github.com/brenhinkeller/StaticMPI.jl/blob/main/test/scripts/mpisendrecv.jl
Brenhin Keller (Jul 23 2022 at 04:25):Turns out there were still a bunch of actual bugs I had to iron out, and once I took care of those I didn't actually need any manual type annotations any more
Brenhin Keller (Jul 23 2022 at 04:26):There are still a bunch of warnings in Cthulhu about constprop being disabled, but it turns out none of them were actually preventing static compilation (just making it a bit harder for me to find where my actual problem was)
Brenhin Keller (Jul 23 2022 at 04:26):So I owe the compiler a bit of an apology :sweat_smile:
Notification Bot (Jul 23 2022 at 04:26):Brenhin Keller has marked this topic as resolved.
Last updated: Nov 06 2024 at 04:40 UTC