[GHC] #16197: Strictness is not preserved under -O1
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- With -O0, the attached code prints: {{{
/usr/local/ghc/ghc-8.4.1.0/bin/ghc -O0 src/foo.hs; and ./src/foo [1 of 1] Compiling Main ( src/foo.hs, src/foo.o ) [Optimisation flags changed] Linking src/foo ... ("exec",0) ("depth",0) ("exec",1) ("depth",0) }}}
But with -O1, it prints: {{{
/usr/local/ghc/ghc-8.4.1.0/bin/ghc -O1 src/foo.hs; and ./src/foo [1 of 1] Compiling Main ( src/foo.hs, src/foo.o ) Linking src/foo ... ("depth",0) ("depth",0) }}}
Reproduced with 8.4.1 and 8.6.2. Doesn't seem to happen under 8.2.0 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by alang9): * Attachment "foo.hs" added. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by nh2): * cc: nh2 (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by carter): 1) what rewrite rules are firing ? 2) more importantly: does disabling rewrite rules under 01 or 02 fix the bug? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by alang9): The bug still appears with `-O1 -fno-enable-rewrite-rules`. The following BUILTIN rules still fire: {{{ Rule fired: Class op null (BUILTIN) Rule fired: Class op foldl' (BUILTIN) Rule fired: Class op null (BUILTIN) Rule fired: Class op foldl' (BUILTIN) Rule fired: Class op >>= (BUILTIN) Rule fired: Class op return (BUILTIN) Rule fired: Class op return (BUILTIN) Rule fired: Class op enumFromTo (BUILTIN) Rule fired: Class op foldl' (BUILTIN) Rule fired: Class op fromInteger (BUILTIN) Rule fired: integerToInt (BUILTIN) Rule fired: Class op show (BUILTIN) Rule fired: Class op show (BUILTIN) Rule fired: Class op return (BUILTIN) Rule fired: Class op showsPrec (BUILTIN) Rule fired: Class op showsPrec (BUILTIN) Rule fired: Class op showsPrec (BUILTIN) Rule fired: Class op showsPrec (BUILTIN) Rule fired: ># (BUILTIN) Rule fired: ==# (BUILTIN) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1
-------------------------------------+-------------------------------------
Reporter: alang9 | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.4.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect result | Unknown/Multiple
at runtime | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Changes (by akio):
* cc: akio (added)
Comment:
I made a smaller test case that I believe exhibits the same issue:
{{{#!hs
data T = T !Bool
data Box a = Box a
f :: Int -> T -> Box Bool
f n t
| n <= 0 = case t of
T b -> Box b
| otherwise = f (n-2) t
f1 :: Int -> Bool -> Box Bool
f1 n t
| n <= 0 = f (-n) $! T t
| otherwise = f1 (n-2) t
g :: Int -> Bool
g k = if k <= 0 then error "crash" else False
{-# NOINLINE g #-}
main :: IO ()
main = case f1 4 (g 0) of
Box _ -> return ()
}}}
With ghc-8.6.2, the above program crashes when compiled with -O0 but not
when compiled with -O1.
It looks like the issue has something to do with strictness analysis.
After the first pass of the demand analyzer, `f` gets the following
strictness signature:
{{{
Str=
#16197: Strictness is not preserved under -O1
-------------------------------------+-------------------------------------
Reporter: alang9 | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.4.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect result | Unknown/Multiple
at runtime | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by simonpj):
I can reproduce this with 8.6, but not with HEAD, so I think perhaps it is
fixed. Hooray.
Indeed we have made some recent changes to the handling of strictness on
data constructors:
{{{
commit d77501cd5b9060e38acd50e11e0c5aae89d75b65
Author: Simon Peyton Jones
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * status: new => patch Comment: Added the test in https://gitlab.haskell.org/ghc/ghc/merge_requests/132 We should probably merge these commits to 8.8 branch if they're not merged already. Ben, updating status to "merge", please close the ticket if the commits on comment:5 are already merged. (I don't know where the 8.8 branch is so I can't check) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * status: patch => merge -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1
-------------------------------------+-------------------------------------
Reporter: alang9 | Owner: (none)
Type: bug | Status: merge
Priority: normal | Milestone:
Component: Compiler | Version: 8.4.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect result | Unknown/Multiple
at runtime | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Ömer Sinan Ağacan
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed * milestone: => 8.8.1 Comment: I'm just going to bump the `ghc-8.8` branch to match `master` as of today. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16197: Strictness is not preserved under -O1 -------------------------------------+------------------------------------- Reporter: alang9 | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.1 Resolution: fixed | Keywords: | DemandAnalysis Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect result | Unknown/Multiple at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => DemandAnalysis -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16197#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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