Unused Registers

[DavePearce]

Minimal example for reproduction:

(module m1)
(defcolumns A B C D)
(deflookup test1 ((+ 1 A) B) (C D))
(deflookup test2 ((+ 1 A)) (C))
(deflookup test3 (A) ((+ 1 C)))

Run with corset debug -Ceeee test.lisp gives this output:

  ID Name                   Type   ×  Reg.
   3 m1.A                      𝔽   1  r0/m1.Aι1
   0 m1.B                      𝔽   1  r1/m1.Bι1
   2 m1.C                      𝔽   1  r2/m1.Cι1
   1 m1.D                      𝔽   1  r3/m1.Dι1
   4 m1.C/#EXPAND[(+ 1 A)]     𝔽   1  r4/m1.C/#EXPAND[(+ 1 A)]ι1
   5 m1.C/#EXPAND[(+ 1 C)]     𝔽   1  r6/m1.C/#EXPAND[(+ 1 C)]ι1   

Here, we can see 5 columns listed. What is less obvious, however, is that there are in fact 6 registers in the list. We can see that r5 is not listed above and, in fact, is a duplicate of m1.C/#EXPAND[(+ 1 A)]. This seems unexpected to me, and suggests a bug in the register allocation mechanism. It also seems that corset is currently working around this.

[DavePearce]

Ok, have managed to put in a fix for this which addresses the example above. There maybe other situations where this could arise --- I didn't check. But they weren't flagged building our large example.