[GHC] #13543: Improve demand analysis for join points
#13543: Improve demand analysis for join points -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider {{{ g :: (Int,Int) -> Int g (p,q) = p+q f :: Int -> Int -> Int f x p = g (join j y = (p,y) in case x of True -> j 3 False -> j 4) }}} If `j` was a vanilla function definition, we'd analyse its body with `evalDmd`, and think that it was lazy in `p`. But for a join point we can do better. We know that `j`'s body (if evaluated at all) will be evaluated with the demand that consumes the entire join-binding, in this case the argument demand from `g`. Whizzo! `g` evaluates both components of its arugment pair, so j is strict in `p`. So, when analysing a join point, we can analyse its body with the demand from the entire join-binding. Another win for join points! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13543 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13543: Improve demand analysis for join points -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => JoinPoints -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13543#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13543: Improve demand analysis for join points
-------------------------------------+-------------------------------------
Reporter: simonpj | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 8.0.1
Resolution: | Keywords: JoinPoints
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Simon Peyton Jones
#13543: Improve demand analysis for join points -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: fixed | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => fixed Comment: Done. No visible effect on nofib, but still good. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13543#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13543: Improve demand analysis for join points
-------------------------------------+-------------------------------------
Reporter: simonpj | Owner: (none)
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 8.0.1
Resolution: fixed | Keywords: JoinPoints
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by alpmestan):
When running `./validate --slow`, I found out that the `T13543` test fails
with all 3 of these ways: `hpc`, `optasm`, `optllvm`.
{{{
=====> T13543(hpc) 1 of 1 [0, 0, 0]
cd "./simplCore/should_compile/T13543.run" && "/home/alp/ghc/inplace/test
spaces/ghc-stage2" -c T13543.hs -dcore-lint -dcmm-lint -no-user-package-db
-rtsopts -fno-warn-missed-specialisations -fshow-warning-groups
-fdiagnostics-color=never -fno-diagnostics-show-caret -dno-debug-output
-O -fhpc -ddump-str-signatures
Actual stderr output differs from expected:
diff -uw "./simplCore/should_compile/T13543.run/T13543.stderr.normalised"
"./simplCore/should_compile/T13543.run/T13543.comp.stderr.normalised"
--- ./simplCore/should_compile/T13543.run/T13543.stderr.normalised
2018-03-08 14:13:19.867965000 +0100
+++ ./simplCore/should_compile/T13543.run/T13543.comp.stderr.normalised
2018-03-08 14:13:19.867965000 +0100
@@ -1 +1,12 @@
+==================== Strictness signatures ====================
+Foo.$trModule: m
+Foo.f:
#13543: Improve demand analysis for join points -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: fixed | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): Hmm, I think the expected test output might just be wrong: the stderr output is empty in the `normal` way because GHC is invoked without optimisation enabled in that way. I believe the test was supposed to expect non-empty output. I suspect we should only be running this test in the `optasm` way (since the other ways will inevitably differ in their strictness signatures) and update the output accordingly. We should ask Simon to look over the new output before committing. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13543#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13543: Improve demand analysis for join points
-------------------------------------+-------------------------------------
Reporter: simonpj | Owner: (none)
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 8.0.1
Resolution: fixed | Keywords: JoinPoints
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by alpmestan):
OK, I'll include this change in my WIP testsuite expectations changes
patch and ask Simon about the "new" expected output (see below for the
program & output).
{{{#!hs
{-# LANGUAGE RankNTypes, GADTs #-}
module Foo where
g :: (Int, Int) -> Int
{-# NOINLINE g #-}
g (p,q) = p+q
f :: Int -> Int -> Int -> Int
f x p q
= g (let j y = (p,q)
{-# NOINLINE j #-}
in
case x of
2 -> j 3
_ -> j 4)
}}}
{{{
==================== Strictness signatures ====================
Foo.$trModule: m
Foo.f:
#13543: Improve demand analysis for join points -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: fixed | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by alpmestan): * cc: alpmestan (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13543#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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