Improve inlining

Currently the contruct

  case (x# ># 0#) of ...

attracts no argument discount for x#, which is silly.

The comment in CoreUnfold says:

	  PrimOpId op  -> primOpSize op (valArgCount args)
			  -- foldr addSize (primOpSize op) (map arg_discount args)
			  -- At one time I tried giving an arg-discount if a primop 
			  -- is applied to one of the function's arguments, but it's
			  -- not good.  At the moment, any unlifted-type arg gets a
			  -- 'True' for 'yes I'm evald', so we collect the discount even
			  -- if we know nothing about it.  And just having it in a primop
			  -- doesn't help at all if we don't know something more.

But the right thing to do seems to be to fix interestingArg in SimplUtils so that it only thinks a primitive-typed thing is interesting if it knows its value (or some structure).

Here's the program that triggered this thought:

import GHC.Word
import GHC.Base
import GHC.Prim

a `shiftRLT` b | b >=# 32# = int2Word# 0#
                | otherwise = a `uncheckedShiftRL#` b

(W32# x#) `shift` (I# i#) =
{- we do an actual case analysis on i# to try to give us a discount -}
   case i# of
    {- For some bizzare reason removing the `shiftRLT` 0# makes the
       inlining fail again -}
    0# -> W32# (x# `shiftRLT` 0#)
    _ -> 
	 if i# >=# 0# then W32# (narrow32Word# (x# `shiftL#` i#))
         else W32# (x# `shiftRLT` negateInt# i#)

x `shiftR` y = x `shift` (-y)

shift7 x = x `shiftR` 7

roconnor@theorem.ca initiated the thread

Trac metadata

Trac field	Value
Version	6.4.2
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown