DEC: support functions with more then 62 arguments (copy #1727) #1730
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(cherry picked from commit f7a4325)
Given
topEntity :: Bool -> Bool -> Bool
topEntity b x = case b of
False -> f x False
True -> f x True
f :: Eq a => a -> a -> Bool
f = ...
DEC would do:
Changes when applying rewrite to:
case b[LocalId] of
False ->
f[GlobalId] @Bool $fEqBool[GlobalId] x[LocalId]
False
True ->
f[GlobalId] @Bool $fEqBool[GlobalId] x[LocalId]
True
Result:
letrec
c$fOut :: Bool
= f[GlobalId] @Bool
(case b[LocalId] of
False ->
$fEqBool[GlobalId]
True ->
$fEqBool[GlobalId])
x[LocalId]
(case b[LocalId] of
False ->
False
True ->
True)
in case b[LocalId] of
False ->
c$fOut[LocalId]
True ->
c$fOut[LocalId]
Because both f's gets the same x argument, in the result the single f
gets the x directly.
But this sharing only worked for LocalId's, for GlobalId's like the
$fEqBool(Eq class dictionary), but clash generates as argument to the
new f:
(case b[LocalId] of
False ->
$fEqBool[GlobalId]
True ->
$fEqBool[GlobalId])
With this patch we now generate:
letrec
c$fOut :: Bool
= f[GlobalId] @Bool $fEqBool[GlobalId]
x[LocalId]
(case b[LocalId] of
False ->
False
True ->
True)
in case b[LocalId] of
False ->
c$fOut[LocalId]
True ->
c$fOut[LocalId]
(cherry picked from commit c5be58b)
GHC's max tuple size has been 62 for a long time, but on master it is now increased to 64. https://gitlab.haskell.org/ghc/ghc/-/commit/6e5a83bb6052f9e251a54026294c87a5bd650c93?merge_request_iid=4146 (cherry picked from commit 2c88533)
So in the next commit we can easily make wrappers around them for big tuples (>62 elements). (cherry picked from commit d2df1b2)
All (non-shared) arguments to DEC'ed functions are combined into tuples, so they can all be defined via a single case expression. But because GHC's tuples are limited to 62 elements, this fails for functions with many arguments. This patch uses GHC's mkChunkified to create (2-levels of) nested tuples for a maximum of 62^2=3844 arguments. Fixes #1669 (cherry picked from commit 28b9a57)
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