T12227 is failing on ghc-8.0

Fresh validate from 5eab189b on x86_64 Linux:

=====> T12227(normal) 1 of 1 [0, 0, 0] 
cd ./perf/compiler &&  "/home/hs01/ezyang/ghc-validate/inplace/test   spaces/ghc-stage2" -c T12227.hs -fforce-recomp -dno-debug-output -fshow-warning-groups -no-user-package-db -rtsopts -fno-warn-tabs -fno-warn-missed-specialisations -fno-ghci-history  -O2 -ddump-hi -ddump-to-file +RTS -M1G +RTS -V0 -tT12227.comp.stats --machine-readable -RTS > T12227.comp.stderr 2>&1
bytes allocated value is too high:
    Expected    T12227(normal) bytes allocated: 1822822016 +/-5%
    Lower bound T12227(normal) bytes allocated: 1731680915 
    Upper bound T12227(normal) bytes allocated: 1913963117 
    Actual      T12227(normal) bytes allocated: 9256914200 
    Deviation   T12227(normal) bytes allocated:      407.8 %
*** unexpected stat test failure for T12227(normal)

That's a pretty awful regression, if it is real.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Visual Haskell
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	bgamari
Operating system
Architecture

changed milestone to %8.0.2

changed weight to 5

added Tbug Trac import labels

Sylvain, this your patch. Any ideas?

Trac metadata

Trac field	Value
CC	bgamari → bgamari, hsyl20@gmail.com

The patch the Edward cites is not the first that shows this failure. I've seen this is a few other cases and have been meaning to track it down. Last time I looked at this I determined that 2756af87 was the first failing commit, although ran out of time before I could replicate it.

I don't think my patch caused this failure: T12227 doesn't even use the FFI.

2756af87 is the patch adding the failing test in ghc-8.0 branch. If it is the first failing commit as @bgamari says, we should check patches from master that have not been cherry-picked into the ghc-8.0 branch (a priori committed in master before 89a8be71 if it validates).

Indeed the patch I cited in ticket:12737#comment:126379 is the patch that adds the failing test. Sadly I don't seeing any relevant patches to compiler/util/Pretty.hs missing from ghc-8.0. Tracking this one down may be a bit tricky. Thankfully the difference is quite large, so comparing ticky profiles from ghc-8.0 and master around the time should be illuminating.

According to ticky, it looks like the primary differences between master (namely 2cb8cc26) and ghc-8.0 (namely d84a824c, which is admittedly quite far removed chronologically from the cherry-picked commit) are indeed in Pretty,

| Change        | alloc A   | alloc B    | name                                                             |      
|---------------|-----------|------------|------------------------------------------------------------------|      
| +3474432240.0 | 262333536 | 3736765776 | beside (ghc:Pretty)                                              |      
| +951367008.0  | 221431440 | 1172798448 | $waboveNest (ghc:Pretty)                                         |      
| +140163848.0  | 91135776  | 231299624  |  (ghc:Coercion.coercionKind_go)                                  |      
| +118356184.0  | 63778576  | 182134760  | $wsplitAtList (ghc:Util.)                                        |      
| +111367360.0  | 640       | 111368000  | $w$cput_6 (ghc:Binary.)                                          |      
| +94517880.0   | 18616520  | 113134400  | $wunpack (ghc:Encoding)                                          |      
| +85860960.0   | 13610200  | 99471160   | $windent (ghc:Pretty)                                            |      
| +45853128.0   | 13206856  | 59059984   | $s$wget1 (ghc:Pretty)                                            |      
| +31953400.0   | 8224616   | 40178016   | $wsep1 (ghc:Pretty.)                                             |      
| +29843944.0   | 8127648   | 37971592   | $wpprName (ghc:Name.)                                            |      
| +29057288.0   | 20964736  | 50022024   | $wsubstTyWith (ghc:TyCoRep.)                                     |      
| +22840864.0   | 11732016  | 34572880   | $wtyCoFVsOfType (ghc:TyCoRep.)                                   |      
| +22640112.0   | 17493648  | 40133760   |  (ghc:TyCon.expandSynTyCon_maybe)                                |      
| +22354288.0   | 5551864   | 27906152   | $wlay2 (ghc:Pretty)                                              |      
| +19673016.0   | 14129160  | 33802176   |  (ghc:Unify.liftCoMatch)                                         |      
| +16728760.0   | 9231400   | 25960160   |  (ghc:Unify.ty_co_match)                                         |      
| +15683720.0   | 9053800   | 24737520   | $wcoercionKindRole (ghc:Coercion.)                               |      
| +15627024.0   | 3566736   | 19193760   |  (ghc:IfaceType.toIfaceTcArgs_go)                                |      
| +15499856.0   | 3545152   | 19045008   | $wget (ghc:Pretty)                                               |      
| +15113200.0   | 5327048   | 20440248   |  (ghc:IfaceType.toIfaceType)                                     |      
| +14813696.0   | 3417088   | 18230784   | $wppr_iface_tc_app (ghc:IfaceType)                               |      
| +14507168.0   | 2747264   | 17254432   |  (ghc:Name.pprModulePrefix)                                      |      
| +13158528.0   | 2774064   | 15932592   | $wxs1 (ghc:Pretty)                                               |      
| +12767416.0   | 5934000   | 18701416   |  (ghc:OptCoercion.opt_co4)                                       |      
| +11420416.0   | 2612848   | 14033264   | $wlay1 (ghc:Pretty)                                              |      
| +11400448.0   | 7529920   | 18930368   | $ssubst_ty (ghc:TyCoRep.composeTCvSubst_)                        |      
| +10744600.0   | 79480     | 10824080   | $w$cput_7 (ghc:IfaceType.)                                       |      
| +10555272.0   | 3780088   | 14335360   |  (ghc:IfaceType.toIfaceTcArgs)                                   |      
| +10380952.0   | 6663952   | 17044904   | isAxiom_maybe (ghc:OptCoercion)                                  |      
...

Working on why this is the case will require some more effort.

changed milestone to %8.0.3

Unfortunately this will need to be resolved in 8.0.3, if at all.

changed milestone to %8.2.1

At this point it is rather unlikely that there will be an 8.0.3. Re-milestoning.

changed milestone to %8.4.1

Given that 8.2.1-rc1 is imminent, I'm bumping these off to the 8.4

changed milestone to %8.6.1

This ticket won't be resolved in 8.4; remilestoning for 8.6. Do holler if you are affected by this or would otherwise like to work on it.

closed

Sadly there has been no motion on this; demilestoning. Do ping if this sounds interesting to you, however.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

reopened

Trac metadata

Trac field	Value
Resolution	ResolvedFixed → Unresolved

added runtime perf label

added Pnormal label

The situation has apparently improved a lot since 8.0.2. Below are the total allocations produced with ghc -fforce-recomp -O2 -ddump-hi -ddump-to-file +RTS -M1G -RTS -Rghc-timing T12227.hs

version	allocations in bytes
8.0.2	9264569728
8.2.2	1028272032
8.4.4	797242400
9.0.1	654268792

closed