Do unsigned remainder on unsigned types

[axch]

Manifestation:

big = 2147483647
rem (big + 1) big
> 4294967295

Expected the answer to be 1.

(Note that big + 1 doesn't overflow the underlying Word32 -- it's just the rem operation messing up).

The cause is

dex-lang/src/lib/ImpToLLVM.hs

Line 614 in c996e98

IRem -> emitInstr (typeOf x) $ L.SRem x y []

, which unconditionally emits a signed remainder instruction, regardless of whether the Dex type is meant to be signed or unsigned.

[axch]

By inspection, I expect IDiv to have the same problem.