[commit: ghc] master: Deserialize IfaceId more lazily (6446254)

[Simon Peyton Jones]

Reid

I beg you to add a comment to these carefully-placed used of laziness!
The informative commit message does not appear in the code :-).

Simon

|  -----Original Message-----
|  From: ghc-commits [mailto:ghc-commits-bounces at haskell.org] On Behalf
|  Of git at git.haskell.org
|  Sent: 03 March 2017 21:36
|  To: ghc-commits at haskell.org
|  Subject: [commit: ghc] master: Deserialize IfaceId more lazily
|  (6446254)
|  
|  Repository : ssh://git@git.haskell.org/ghc
|  
|  On branch  : master
|  Link       :
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|  >---------------------------------------------------------------
|  
|  commit 644625449a9b6fbeb9a81f1a7d0e7d18424fb707
|  Author: Reid Barton <rwbarton at gmail.com>
|  Date:   Fri Mar 3 15:49:38 2017 -0500
|  
|      Deserialize IfaceId more lazily
|  
|      This change sped up the total validate --build-only time by 0.8%
|      on my test system; hopefully a representative result.
|  
|      I didn't bother making the other constructors lazy because for
|      IfaceData and IfaceClass we need to pull on some of the fields
|      in loadDecl, and all the others seem much more rare than IfaceId.
|  
|      Test Plan: validate, perf
|  
|      Reviewers: austin, bgamari
|  
|      Reviewed By: bgamari
|  
|      Subscribers: thomie
|  
|      Differential Revision: https://phabricator.haskell.org/D3269
|  
|  
|  >---------------------------------------------------------------
|  
|  644625449a9b6fbeb9a81f1a7d0e7d18424fb707
|   compiler/iface/IfaceSyn.hs | 8 ++------
|   1 file changed, 2 insertions(+), 6 deletions(-)
|  
|  diff --git a/compiler/iface/IfaceSyn.hs b/compiler/iface/IfaceSyn.hs
|  index d73a738..1c30476 100644
|  --- a/compiler/iface/IfaceSyn.hs
|  +++ b/compiler/iface/IfaceSyn.hs
|  @@ -1565,9 +1565,7 @@ instance Binary IfaceDecl where
|       put_ bh (IfaceId name ty details idinfo) = do
|           putByte bh 0
|           putIfaceTopBndr bh name
|  -        put_ bh ty
|  -        put_ bh details
|  -        put_ bh idinfo
|  +        lazyPut bh (ty, details, idinfo)
|  
|       put_ bh (IfaceData a1 a2 a3 a4 a5 a6 a7 a8 a9) = do
|           putByte bh 2
|  @@ -1657,9 +1655,7 @@ instance Binary IfaceDecl where
|           h <- getByte bh
|           case h of
|               0 -> do name    <- get bh
|  -                    ty      <- get bh
|  -                    details <- get bh
|  -                    idinfo  <- get bh
|  +                    ~(ty, details, idinfo) <- lazyGet bh
|                       return (IfaceId name ty details idinfo)
|               1 -> error "Binary.get(TyClDecl): ForeignType"
|               2 -> do a1  <- getIfaceTopBndr bh
|  
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