[commit: ghc] master: extend '-fmax-worker-args' limit to specialiser (Trac #11565) (f93c363)
git at git.haskell.org
git at git.haskell.org
Fri Sep 2 20:45:28 UTC 2016
Repository : ssh://git@git.haskell.org/ghc
On branch : master
Link : http://ghc.haskell.org/trac/ghc/changeset/f93c363fab1ac8ce6f0b474f5967b0b097995827/ghc
>---------------------------------------------------------------
commit f93c363fab1ac8ce6f0b474f5967b0b097995827
Author: Sergei Trofimovich <slyfox at gentoo.org>
Date: Fri Sep 2 18:47:56 2016 +0100
extend '-fmax-worker-args' limit to specialiser (Trac #11565)
It's a complementary change to
a48de37dcca98e7d477040b0ed298bcd1b3ab303
restore -fmax-worker-args handling (Trac #11565)
I don't have a small example but I've noticed another
discrepancy when was profiling GHC for performance
cmmExprNative :: ReferenceKind -> CmmExpr -> CmmOptM CmmExpr
was specialised by 'spec_one' down to a function with arity 159.
As a result 'perf record' pointed at it as at slowest
function in whole ghc library.
I've extended -fmax-worker-args effect to 'spec_one'
as it does the same worker/wrapper split to push
arguments to the heap.
The change decreases heap usage on a synth.bash benchmark
(Trac #9221) from 67G down to 64G (-4%). Benchmark runtime
decreased from 14.5 s down to 14.s (-7%).
Signed-off-by: Sergei Trofimovich <siarheit at google.com>
Reviewers: ezyang, simonpj, austin, goldfire, bgamari
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2507
GHC Trac Issues: #11565
>---------------------------------------------------------------
f93c363fab1ac8ce6f0b474f5967b0b097995827
compiler/specialise/SpecConstr.hs | 12 ++++++++----
compiler/stranal/WwLib.hs | 14 +++++++++-----
2 files changed, 17 insertions(+), 9 deletions(-)
diff --git a/compiler/specialise/SpecConstr.hs b/compiler/specialise/SpecConstr.hs
index 8cc393c..1cf3d44 100644
--- a/compiler/specialise/SpecConstr.hs
+++ b/compiler/specialise/SpecConstr.hs
@@ -29,7 +29,7 @@ import CoreFVs ( exprsFreeVarsList )
import CoreMonad
import Literal ( litIsLifted )
import HscTypes ( ModGuts(..) )
-import WwLib ( mkWorkerArgs )
+import WwLib ( isWorkerSmallEnough, mkWorkerArgs )
import DataCon
import Coercion hiding( substCo )
import Rules
@@ -1533,10 +1533,14 @@ specialise env bind_calls (RI { ri_fn = fn, ri_lam_bndrs = arg_bndrs
| Just all_calls <- lookupVarEnv bind_calls fn
= -- pprTrace "specialise entry {" (ppr fn <+> ppr (length all_calls)) $
- do { (boring_call, pats) <- callsToPats env specs arg_occs all_calls
-
+ do { (boring_call, all_pats) <- callsToPats env specs arg_occs all_calls
-- Bale out if too many specialisations
- ; let n_pats = length pats
+ ; let pats = filter (is_small_enough . fst) all_pats
+ is_small_enough vars = isWorkerSmallEnough (sc_dflags env) vars
+ -- We are about to construct w/w pair in 'spec_one'.
+ -- Omit specialisation leading to high arity workers.
+ -- See Note [Limit w/w arity]
+ n_pats = length pats
spec_count' = n_pats + spec_count
; case sc_count env of
Just max | not (sc_force env) && spec_count' > max
diff --git a/compiler/stranal/WwLib.hs b/compiler/stranal/WwLib.hs
index 1a09605..64de0e0 100644
--- a/compiler/stranal/WwLib.hs
+++ b/compiler/stranal/WwLib.hs
@@ -8,6 +8,7 @@
module WwLib ( mkWwBodies, mkWWstr, mkWorkerArgs
, deepSplitProductType_maybe, findTypeShape
+ , isWorkerSmallEnough
) where
#include "HsVersions.h"
@@ -143,7 +144,8 @@ mkWwBodies dflags fam_envs fun_ty demands res_info
wrapper_body = wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_call_args . Var
worker_body = mkLams work_lam_args. work_fn_str . work_fn_cpr . work_fn_args
- ; if is_small_enough work_args && (useful1 && not only_one_void_argument || useful2)
+ ; if isWorkerSmallEnough dflags work_args
+ && (useful1 && not only_one_void_argument || useful2)
then return (Just (worker_args_dmds, wrapper_body, worker_body))
else return Nothing
}
@@ -163,10 +165,12 @@ mkWwBodies dflags fam_envs fun_ty demands res_info
= True
| otherwise
= False
- is_small_enough args = count isId args <= maxWorkerArgs dflags
- -- See Note [Limit w/w arity]
- -- We count only Free variables (isId) to skip Type, Kind
- -- variables which have no runtime representation.
+
+-- See Note [Limit w/w arity]
+isWorkerSmallEnough :: DynFlags -> [Var] -> Bool
+isWorkerSmallEnough dflags vars = count isId vars <= maxWorkerArgs dflags
+ -- We count only Free variables (isId) to skip Type, Kind
+ -- variables which have no runtime representation.
{-
Note [Always do CPR w/w]
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