diff options
| author | Simon Peyton Jones <simonpj@microsoft.com> | 2021-02-08 22:46:32 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2021-02-12 14:16:16 +0000 |
| commit | 101b242a23a72a140f3ca2248732847401084da3 (patch) | |
| tree | b1a1d606200bfca42e24a1594691fd1fa79b5a5a /compiler/GHC/Iface/Rename.hs | |
| parent | 40983d2331fe34c0af6925db7588d5ac6a19ae36 (diff) | |
| download | haskell-wip/T19336.tar.gz | |
Fix a serious bug in roughMatchTcswip/T19336
The roughMatchTcs function enables a quick definitely-no-match test
in lookupInstEnv. Unfortunately, it didn't account for type families.
This didn't matter when type families were flattened away, but now
they aren't flattened it matters a lot.
The fix is very easy. See INVARIANT in GHC.Core.InstEnv
Note [ClsInst laziness and the rough-match fields]
Fixes #19336
The change makes compiler perf worse on two very-type-family-heavy
benchmarks, T9872{a,d}:
T9872a(normal) ghc/alloc 2172536442.7 2216337648.0 +2.0%
T9872d(normal) ghc/alloc 614584024.0 621081384.0 +1.1%
(Everything else is 0.0% or at most 0.1%.)
I think we just have to put up with this. Some cases were being
wrongly filtered out by roughMatchTcs that might actually match, which
could lead to false apartness checks. And it only affects these very
type-family-heavy cases.
Metric Increase:
T9872a
T9872d
Diffstat (limited to 'compiler/GHC/Iface/Rename.hs')
| -rw-r--r-- | compiler/GHC/Iface/Rename.hs | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/compiler/GHC/Iface/Rename.hs b/compiler/GHC/Iface/Rename.hs index f523d24625..cd97c000a8 100644 --- a/compiler/GHC/Iface/Rename.hs +++ b/compiler/GHC/Iface/Rename.hs @@ -414,7 +414,7 @@ rnIfaceNeverExported name = do rnIfaceClsInst :: Rename IfaceClsInst rnIfaceClsInst cls_inst = do n <- rnIfaceGlobal (ifInstCls cls_inst) - tys <- mapM rnMaybeIfaceTyCon (ifInstTys cls_inst) + tys <- mapM rnRoughMatchTyCon (ifInstTys cls_inst) dfun <- rnIfaceNeverExported (ifDFun cls_inst) return cls_inst { ifInstCls = n @@ -422,14 +422,14 @@ rnIfaceClsInst cls_inst = do , ifDFun = dfun } -rnMaybeIfaceTyCon :: Rename (Maybe IfaceTyCon) -rnMaybeIfaceTyCon Nothing = return Nothing -rnMaybeIfaceTyCon (Just tc) = Just <$> rnIfaceTyCon tc +rnRoughMatchTyCon :: Rename (Maybe IfaceTyCon) +rnRoughMatchTyCon Nothing = return Nothing +rnRoughMatchTyCon (Just tc) = Just <$> rnIfaceTyCon tc rnIfaceFamInst :: Rename IfaceFamInst rnIfaceFamInst d = do fam <- rnIfaceGlobal (ifFamInstFam d) - tys <- mapM rnMaybeIfaceTyCon (ifFamInstTys d) + tys <- mapM rnRoughMatchTyCon (ifFamInstTys d) axiom <- rnIfaceGlobal (ifFamInstAxiom d) return d { ifFamInstFam = fam, ifFamInstTys = tys, ifFamInstAxiom = axiom } |