This PR adds “non-branching case statements”: For each inductive
constructor `T.con` this adds a function `T.con.with` that is similar
`T.casesOn`, but has only one arm (the one for `con`), and an additional
`t.toCtorIdx = 12` assumption.
For example:
```lean
inductive Vec (α : Type) : Nat → Type where
| nil : Vec α 0
| cons {n} : α → Vec α n → Vec α (n + 1)
/--
info: @[reducible] protected def Vec.cons.elim.{u} : {α : Type} →
{motive : (a : Nat) → Vec α a → Sort u} →
{a : Nat} →
(t : Vec α a) →
t.ctorIdx = 1 → ({n : Nat} → (a : α) → (a_1 : Vec α n) → motive (n + 1) (Vec.cons a a_1)) → motive a t
-/
#guard_msgs in
#print sig Vec.cons.elim
```
This is a building block for non-quadratic implementations of `BEq` and
`DecidableEq` etc.
Builds on top of #9951.
The compiled code for a these functions could presumably, without
branching on the inductive value, directly access the fields. Achieving
this optimization (and achieving it without a quadratic compilation
cost) is not in scope for this PR.
This PR creates the deprecated `.toCtorIdx` alias only for enumeration
types, which are the types that used to have this function. No need
generating an alias for types that never had it. Should reduce the
number of symbols in the standard library.
This PR generates `.ctorIdx` functions for all inductive types, not just
enumeration types. This can be a building block for other constructions
(`BEq`, `noConfusion`) that are size-efficient even for large
inductives.
It also renames it from `.toCtorIdx` to `.ctorIdx`, which is the more
idiomatic naming.
The old name exists as an alias, with a deprecation attribute to be
added after the next
stage0 update.
These functions can arguably compiled down to a rather efficient tag
lookup, rather than a `case` statement. This is future work (but
hopefully near future).
For a fair number of basic types the compiler is not able to compile a
function using `casesOn` until further definitions have been defined.
This therefore (ab)uses the `genInjectivity` flag and
`gen_injective_theorems%` command to also control the generation of this
construct.
For (slightly) more efficient kernel reduction one could use `.rec`
rather than `.casesOn`. I did not do that yet, also because it
complicates compilation.
This PR fixes an issue when running Mathlib's `FintypeCat` as code,
where an erased type former is passed to a polymorphic function. We were
lowering the arrow type to`object`, which conflicts with the runtime
representation of an erased value as a tagged scalar.
This PR changes `IRType.boxed` to map `erased` to `tobject` rather than
`object`, since `erased` has a representation of a boxed scalar 0 when
we are forced to represent it at runtime. This case does not occur at
all in the Lean codebase.
This PR changes ToIR to call `lowerEnumToScalarType?` with
`ConstructorVal.induct` rather than the name of the constructor itself.
This was an oversight in some refactoring of code in the new compiler
before landing it. It should not affect runtime of compiled code (due to
the extra tagging/untagging being optimized by LLVM), but it does make
IR for the interpreter slightly more efficient.
This PR enables code generation to proceed in parallel to further
elaboration.
It does not aim to make further refinements such as generating code for
different declarations in parallel or removing the dependency on kernel
checking.
