Integer constant folding in the presence of new primops

[Simon Peyton-Jones]

Jan

I'm conscious that we have not closed the loop on this thread, below.  (I think the attached email is also relevant.) 

If it's not sorted out, can you open a ticket, put in the relevant info (so we don't need to look at the email trail), and we can tackle it when you get here.

Simon

-----Original Message-----
From: ghc-devs-bounces at haskell.org [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Jan Stolarek
Sent: 20 May 2013 12:35
To: Ian Lynagh
Cc: ghc-devs at haskell.org
Subject: Re: Integer constant folding in the presence of new primops

> If you remove everything but the quotInteger test from 
> integerConstantFolding and compile with -ddump-rule-rewrites then 
> you'll see that the eqInteger rule fires before quotInteger. This is 
> presumably comparing against 0, as the definition of quot for Integer 
> (in GHC.Real) is
>     _ `quot` 0 = divZeroError
>     n `quot` d = n `quotInteger` d
Yes, I noticed these two rules firing together - perhaps that's the explanation why. I created a small program for testing:

main = print quotInt
quotInt :: Integer
quotInt = 100063 `quot` 156

I noticed that when I define eqInteger wrapper to be NOINLINE, the call to quot is translated to Core as:

Main.quotInt =
  GHC.Real.$fIntegralInteger_$cquot
    (__integer 100063) (__integer 156)

but when I change the wrapper to INLINE I get:

Main.quotInt =
  GHC.Real.$fNumRatio_$cquot             <-------- NumRatio instead of IntegralInteger
    (__integer 100063) (__integer 156)

All rule firing happens later (I used -ddump-simpl-iterations -ddump-rule-firings), except that for $fNumRatio_$cquot the quot rules don't fire.

> Do you also still have eqInteger wired in? It sounds like you might 
> have given them both the same unique?
No, they didn't have the same unique. I modified the existing rules to work on the new primops and ignore their wrappers. At the moment I reverted these changes so that I can make progress and leave this problem for later.

Janek

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