[commit: ghc] wip/T10293: Call Arity: Trade precision for performance in large mutually recursive groups (2f3aa54)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/T10293
Link       : http://ghc.haskell.org/trac/ghc/changeset/2f3aa542cf9db37360925c27bd6646a1ce9dd852/ghc

>---------------------------------------------------------------

commit 2f3aa542cf9db37360925c27bd6646a1ce9dd852
Author: Joachim Breitner <mail at joachim-breitner.de>
Date:   Wed Apr 15 16:25:13 2015 +0200

    Call Arity: Trade precision for performance in large mutually recursive groups
    
    Sometimes (especial with derived Data instances, it seems), one can have
    very large mutually recursive bindings. Calculating the Call Arity
    analysis result with full precision is an expensive operation in these
    case. So above a certain threshold (25, for no good reason besides
    intuition), skip this calculation and assume the recursion is not
    linear, which is a conservative result.
    
    With this, the Call Arity analysis accounts for 3.7% of the compile time
    of haskell-src-exts.


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2f3aa542cf9db37360925c27bd6646a1ce9dd852
 compiler/simplCore/CallArity.hs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/compiler/simplCore/CallArity.hs b/compiler/simplCore/CallArity.hs
index 4e4555c..c2a5ad0 100644
--- a/compiler/simplCore/CallArity.hs
+++ b/compiler/simplCore/CallArity.hs
@@ -630,6 +630,9 @@ callArityRecEnv any_boring ae_rhss ae_body
     cross_calls
         -- See Note [Taking boring variables into account]
         | any_boring          = completeGraph (domRes ae_combined)
+        -- Also, calculating cross_calls is expensive. Simply be conservative
+        -- if the mutually recursive group becomes too large.
+        | length ae_rhss > 25 = completeGraph (domRes ae_combined)
         | otherwise           = unionUnVarGraphs $ map cross_call ae_rhss
     cross_call (v, ae_rhs) = completeBipartiteGraph called_by_v called_with_v
       where