[GHC] #2163: GHC makes thunks for Integers we are strict in

Don Stewart dons at galois.com
Wed Mar 19 19:51:53 EDT 2008

```igloo:
> On Wed, Mar 19, 2008 at 05:31:08PM +0000, Ian Lynagh wrote:
> > On Tue, Mar 18, 2008 at 04:12:35PM -0000, GHC wrote:
> > >
> > >  (don't worry, this often catches me out too.  Perhaps a strict let
> > >  should be indicated more explicitly in `-ddump-simpl`).
> >
> > I'd certainly find it useful if it was clearer.
>
> In fact, simpl hides more than I'd realised. With these definitions:
>
>     f :: Integer -> Integer -> Integer -> Integer
>     f x y z | y == 1 = x * z
>             | otherwise = f (x * x) y (z * z)
>
>     g :: Integer -> Integer -> Integer -> Integer
>     g x y z | y == 1 = x
>             | otherwise = g (x * x) y (z * z)
>
> simpl shows
>
>     B.f (GHC.Num.timesInteger x_a5B x_a5B) y_a5D
>         (GHC.Num.timesInteger z_a5F z_a5F);
>
> and
>
>     B.g (GHC.Num.timesInteger x_a74 x_a74) y_a76
>         (GHC.Num.timesInteger z_a78 z_a78);
>
> for the recursive calls, although in the STG you can see that the
> multiplication of z is done strictly in f but not g (which is correct,
> as g is not strict in z).
>
> So perhaps the solution is just that I should look at the STG rather
> than the simpl when I want to see what's going on.
>
>
> Thanks

We really need an official and blessed view of the optimised core, with
full, relevant information, in human readable form.

Just simplifiying the obvious qualified names would be a start, and
some simple alpha renaming.

-- Don
```