cgCase of PrimAlts needs care in new codegen

The following code,

module Spring where

import Data.Array.Unboxed

type Arr = UArray Int Double
data Spring = Spring !Double !Int !Arr deriving Show

step :: Double -> Spring -> Spring
step h (Spring k sz y) = let
    f arr = listArray (0, 2*sz-1) (velocity ++ accel)
      where
        velocity = [arr ! i | i <- [sz .. 2*sz-1]]
        k'       = k * fromIntegral sz^2
        accel    = [0] ++ [k' * (arr!(i-1) - 2 * arr!i + arr!(i+1))
                           | i <- [1 .. sz-2]]
                   ++ [k' * (arr!(sz-2) - arr!(sz-1))]
    (.*) :: Double -> Arr -> Arr
    a .* b  = listArray (0, 2*sz-1) $ map (a*) (elems b)
    (<+>) :: Arr -> Arr -> Arr
    a <+> b = listArray (0, 2*sz-1) $ zipWith (+) (elems a) (elems b)
    -- order 4 Runge-Kutta
    k1 = h .* f y
    k2 = h .* f (y <+> (0.5 .* k1))
    k3 = h .* f (y <+> (0.5 .* k2))
    k4 = h .* f (y <+> k3)
    y' = y <+> ((1/6) .* (k1 <+> (2 .* (k2 <+> k3)) <+> k4))
  in
    Spring k sz y'

doesn't compile with optimization in ghc-6.11:

# ghc -O -c Bug.hs
/tmp/ghc12296_0/ghc12296_0.s: Assembler messages:

/tmp/ghc12296_0/ghc12296_0.s:2355:0:
     Error: bad register name `%st(-8)'

/tmp/ghc12296_0/ghc12296_0.s:2384:0:
     Error: bad register name `%st(-8)'

/tmp/ghc12296_0/ghc12296_0.s:2563:0:
     Error: bad register name `%st(-8)'

/tmp/ghc12296_0/ghc12296_0.s:2602:0:
     Error: bad register name `%st(-8)'

/tmp/ghc12296_0/ghc12296_0.s:3006:0:
     Error: bad register name `%fake0'

/tmp/ghc12296_0/ghc12296_0.s:3023:0:
     Error: bad register name `%fake0'

It's odd, first it tries to assign a closure pointer to an FPU register:

        movl $r1sa_closure,%fake0

and later it uses register 0 (%eax) as an operand to an FPU operation:

#       gsubl %fake1,%eax,%fake1
        #GSUB-xxxcase1
        ffree %st(7) ; fld %st(-8) ; fsubrp %st(0),%st(2)

Using -fregs-graph didn't help.

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (NCG)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture