JuliaLang / julia / 1085

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Commit Message

inference: Don't intersect a field alias with its parent slot in `from_interconditional` (#64028)

`from_interconditional` looks for the first call argument that the callee's
`InterConditional` can refine, then intersects the refinements of every
argument that refers to the same object. It identified a `MustAlias`
argument by the slot holding the parent object, so a field alias such as
`nt.n` was treated as the same object as `nt` itself. When `f` refines `nt`
in `f(nt, nt.n)`, the parent's refinement was met with the field's, which
inferred the call as `Union{}` or refined the field to the parent's type.

Track explicitly whether the refinement target is a slot or a field alias:
a `MustAlias` argument can only start a new target, and a slot holding a
`MustAlias` whose field type isn't a `Type` now refines the aliased field
instead of forming a `Conditional` on the parent slot with the field's type.

Since #47574 made `NativeInterpreter` use `MustAlias`, this miscompiles
native code. On 1.13 it affects external interpreters that use
`MustAliasesLattice`, such as JET.jl.

Fixes #63981

Assisted-by: Claude Code (Opus 5.5)

Coverage Stats

6 of 6 new or added lines in 1 file covered. (100.0%)

426 existing lines in 6 files now uncovered.

95476 of 107330 relevant lines covered (88.96%)

344.55 hits per line