Use a map to implement litToArrayPreimage

[gustavo-grieco]

Description

In certain runs, litToArrayPreimage was taking most of the execution time so this is an optimized version of it using maps

Checklist

• tested locally
• added automated tests
• updated the docs
• updated the changelog

[blishko]

Can you provide some examples and measurements?

[msooseth]

Wait, doesn't Haskell do memoization of such pure functions by default? I though this will only be computed once and then memoized... maybe I am wrong? If not, maybe we could simply add Memoizable as per: https://wiki.haskell.org/Memoization

What do you think?

[msooseth]

Haha, I'm an idiot. There is no such Memoizable Monad and memoization is clearly not the default. OK, so this is likely needed, actually...

[msooseth]

@blishko keccak is actually annoyingly slow and this thing needs to be recomputed every time if it's not memoized, which is likely pretty expensive. I just somehow thought this cannot possibly be non-memoized, but it seems like I was wrong....

[msooseth]

Let's remove the comment here, I think it's okay without.

[gustavo-grieco]

Here is a profiling run from around 15 minutes of the exploration of a swap function where the 100% of time spent in the interpret function. Without the patch:

COST CENTRE        MODULE                 SRC                                               %time %alloc

splitSExpr         EVM.Solvers            src/EVM/Solvers.hs:(463,1)-(472,52)                32.1   14.4
writeBytes         EVM.SMT                src/EVM/SMT.hs:(915,1)-(929,76)                    16.7    3.0
litToArrayPreimage EVM.Expr               src/EVM/Expr.hs:(760,1)-(765,19)                   12.4    0.0
getSExpr           EVM.Solvers            src/EVM/Solvers.hs:(478,1)-(492,75)                 8.6   13.4
sendLine           EVM.Solvers            src/EVM/Solvers.hs:(421,1)-(424,45)                 8.1   24.8
readWordFromBytes  EVM.Expr               src/EVM/Expr.hs:(298,1)-(307,44)                    3.7    4.3
exprToSMT          EVM.SMT                src/EVM/SMT.hs:(648,1)-(828,105)                    3.2    9.0
untilFixpoint      EVM.Types              src/EVM/Types.hs:(1565,1)-(1569,27)                 2.0    5.2
mapExprM           EVM.Traversals         src/EVM/Traversals.hs:(269,1)-(590,20)              1.7    5.6
readByte           EVM.Expr               src/EVM/Expr.hs:(225,1)-(258,31)                    1.6    0.5
maybeTryFrom       Witch.Utility          source/library/Witch/Utility.hs:(124,1)-(126,19)    1.1    1.4
sendScript         EVM.Solvers            src/EVM/Solvers.hs:(387,1)-(396,108)                0.6    1.7
sp                 EVM.SMT                src/EVM/SMT.hs:831:1-35                             0.5    1.0
splitSMGen         System.Random.SplitMix src/System/Random/SplitMix.hs:(225,1)-(229,31)      0.2    1.2
encode             Data.Serialize         src/Data/Serialize.hs:109:1-21                      0.1    2.8

And with the patch:

COST CENTRE       MODULE                 SRC                                               %time %alloc

splitSExpr        EVM.Solvers            src/EVM/Solvers.hs:(463,1)-(472,52)                37.8   16.9
sendLine          EVM.Solvers            src/EVM/Solvers.hs:(421,1)-(424,45)                14.2   27.1
getSExpr          EVM.Solvers            src/EVM/Solvers.hs:(478,1)-(492,75)                12.9   15.0
writeBytes        EVM.SMT                src/EVM/SMT.hs:(915,1)-(929,76)                    12.7    3.0
exprToSMT         EVM.SMT                src/EVM/SMT.hs:(648,1)-(828,105)                    4.1    9.5
readWordFromBytes EVM.Expr               src/EVM/Expr.hs:(298,1)-(307,44)                    3.6    3.2
mapExprM          EVM.Traversals         src/EVM/Traversals.hs:(269,1)-(590,20)              1.6    4.8
readByte          EVM.Expr               src/EVM/Expr.hs:(225,1)-(258,31)                    1.4    0.4
MAIN              MAIN                   <built-in>                                          1.3    0.1
untilFixpoint     EVM.Types              src/EVM/Types.hs:(1565,1)-(1569,27)                 1.2    2.2
sendScript        EVM.Solvers            src/EVM/Solvers.hs:(387,1)-(396,108)                1.1    1.9
maybeTryFrom      Witch.Utility          source/library/Witch/Utility.hs:(124,1)-(126,19)    0.9    1.0
sp                EVM.SMT                src/EVM/SMT.hs:831:1-35                             0.7    1.2
splitSMGen        System.Random.SplitMix src/System/Random/SplitMix.hs:(225,1)-(229,31)      0.2    1.2
encode            Data.Serialize         src/Data/Serialize.hs:109:1-21                      0.1    2.2

[blishko]

How can I reproduce this?

[blishko]

I think this will be good, but I think we can clean it up a bit.

[blishko]

I don't think we need to store imageHash + 255 in the value.

[gustavo-grieco]

Removed!

[gustavo-grieco]

I'm coming back to this, sorry for the delay

[gustavo-grieco]

All tests are passing, so feel free to take another look if needed. Should I update the changelog about it?

[blishko]

Can you please rebase on top of main? I would like to run a bit of benchmarking.

I don't think changelog entry is necessary for this change.