#15226: GHC doesn't know that seq# produces something in WHNF
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Reporter: dfeuer | Owner: (none)
Type: bug | Status: merge
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.4.3
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: Runtime | Test Case:
performance bug | perf/should_run/T15226, 15226a
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D4796
Wiki Page: |
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Changes (by simonpj):
* testcase: => perf/should_run/T15226, 15226a
Comment:
I believe this is a follow-up patch
{{{
commit 502026fc0a35460c7f04b26a11320723a7bbfdff
Author: David Feuer
---------------------------------------------------------------
502026fc0a35460c7f04b26a11320723a7bbfdff compiler/coreSyn/CoreSyn.hs | 3 ++- testsuite/tests/perf/should_run/{T15226.hs => T15226a.hs} | 5 ++++- testsuite/tests/perf/should_run/all.T | 9 +++++++++ 3 files changed, 15 insertions(+), 2 deletions(-) diff --git a/compiler/coreSyn/CoreSyn.hs b/compiler/coreSyn/CoreSyn.hs index 4dd70b0..50e40d1 100644 --- a/compiler/coreSyn/CoreSyn.hs +++ b/compiler/coreSyn/CoreSyn.hs @@ -2046,10 +2046,11 @@ collectArgs expr go e as = (e, as) -- | Attempt to remove the last N arguments of a function call. --- Strip off any ticks encountered along the way and any ticks +-- Strip off any ticks or coercions encountered along the way and any -- at the end. stripNArgs :: Word -> Expr a -> Maybe (Expr a) stripNArgs !n (Tick _ e) = stripNArgs n e +stripNArgs n (Cast f _) = stripNArgs n f stripNArgs 0 e = Just e stripNArgs n (App f _) = stripNArgs (n - 1) f stripNArgs _ _ = Nothing diff --git a/testsuite/tests/perf/should_run/T15226.hs b/testsuite/tests/perf/should_run/T15226a.hs similarity index 89% copy from testsuite/tests/perf/should_run/T15226.hs copy to testsuite/tests/perf/should_run/T15226a.hs index 4c09114..6e9a1db 100644 --- a/testsuite/tests/perf/should_run/T15226.hs +++ b/testsuite/tests/perf/should_run/T15226a.hs @@ -3,6 +3,7 @@ import Control.Exception (evaluate) -- Just in case Prelude.repeat changes for some reason. import Prelude hiding (repeat) +import Data.Coerce -- We want to be sure that the compiler *doesn't* know that -- all the elements of the list are in WHNF, because if it @@ -12,11 +13,13 @@ repeat a = res where res = a : res {-# NOINLINE repeat #-} -- Belt *and* suspenders +newtype Foo = Foo Int + silly :: [Int] -> IO () silly = foldr go (pure ()) where go x r = do - x' <- evaluate x + x' <- (coerce (evaluate :: Foo -> IO Foo) :: Int -> IO Int) x evaluate (x' + 3) -- GHC should know that x' has been evaluated, -- so this calculation will be erased entirely. -- Otherwise, we'll create a thunk to pass to diff --git a/testsuite/tests/perf/should_run/all.T b/testsuite/tests/perf/should_run/all.T index b248dd5..0e7996ef 100644 --- a/testsuite/tests/perf/should_run/all.T +++ b/testsuite/tests/perf/should_run/all.T @@ -584,3 +584,12 @@ test('T15226', only_ways(['normal'])], compile_and_run, ['-O']) + +test('T15226a', + [stats_num_field('bytes allocated', + [ (wordsize(64), 41040, 5) ]), + # 2018-06-06 41040 Look through casts for seq# + # initial 400041040 + only_ways(['normal'])], + compile_and_run, + ['-O']) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15226#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler