Generic dispatch through a supertrait emits an invalid evidence GEP #3

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opened 2026-06-15 14:08:18 +02:00 by st · 0 comments

st commented

2026-06-15 14:08:18 +02:00

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Repro

fn f[T: Int](a: T, b: T): T = Num.add(a, b)   // Num is Int's supertrait
fn main(): i64 = f(1, 2)

LLVM verification fails: Invalid indices for GEP pointer type!

%dict_slot_1 = getelementptr inbounds nuw { { ptr, ptr } }, ptr %evidence, i32 0, i32 1

The evidence struct for a T: Int constraint has one slot, but supertrait (Num) dispatch indexes slot 1.

Also hit by examples/supertraits.aml (same root cause).

Codegen area: evidence/vtable layout for constrained type params.

Repro ``` fn f[T: Int](a: T, b: T): T = Num.add(a, b) // Num is Int's supertrait fn main(): i64 = f(1, 2) ``` LLVM verification fails: Invalid indices for GEP pointer type! `%dict_slot_1 = getelementptr inbounds nuw { { ptr, ptr } }, ptr %evidence, i32 0, i32 1` The evidence struct for a T: Int constraint has one slot, but supertrait (Num) dispatch indexes slot 1. Also hit by examples/supertraits.aml (same root cause). Codegen area: evidence/vtable layout for constrained type params.