compiler: map `core::mem::swap` to the pure swap

In the pure functional model, `swap` is mostly about borrow checking and
should simplify to the pure swap in our backends.

Other backends than Lean are not done in this commit.

Signed-off-by: Ryan Lahfa <ryan.lahfa@inria.fr>

3 files changed, 4 insertions, 6 deletions

diff --git a/backends/lean/Base/Primitives/Base.lean b/backends/lean/Base/Primitives/Base.lean
index 62546ac3..94134d86 100644
--- a/backends/lean/Base/Primitives/Base.lean
+++ b/backends/lean/Base/Primitives/Base.lean
@@ -132,6 +132,8 @@ def Result.attach {α: Type} (o : Result α): Result { x : α // o = ok x } :=
 @[simp] def core.mem.replace (a : Type) (x : a) (_ : a) : a × a := (x, x)
 /- [core::option::Option::take] -/
 @[simp] def Option.take (T: Type) (self: Option T): Option T × Option T := (self, .none)
+/- [core::mem::swap] -/
+@[simp] def core.mem.swap (T: Type) (a b: T): T × T := (b, a)
 
 /-- Aeneas-translated function -- useful to reduce non-recursive definitions.
  Use with `simp [ aeneas ]` -/
diff --git a/compiler/ExtractBuiltin.ml b/compiler/ExtractBuiltin.ml
index 3e96c320..531f1d8b 100644
--- a/compiler/ExtractBuiltin.ml
+++ b/compiler/ExtractBuiltin.ml
@@ -287,6 +287,7 @@ let builtin_funs () : (pattern * bool list option * builtin_fun_info) list =
   in
   [
     mk_fun "core::mem::replace" None None;
+    mk_fun "core::mem::swap" None None;
     mk_fun "core::slice::{[@T]}::len"
       (Some (backend_choice "slice::len" "Slice::len"))
       None;
@@ -517,6 +518,7 @@ let builtin_fun_effects =
       "alloc::vec::{alloc::vec::Vec<@T, alloc::alloc::Global>}::new";
       "alloc::vec::{alloc::vec::Vec<@T, @A>}::len";
       "core::mem::replace";
+      "core::mem::swap";
       "core::mem::take";
       "core::option::{core::option::Option<@T>}::take";
       "core::clone::impls::{core::clone::Clone<bool>}::clone";
diff --git a/tests/lean/External/FunsExternal_Template.lean b/tests/lean/External/FunsExternal_Template.lean
index 38151dc9..f0e771f7 100644
--- a/tests/lean/External/FunsExternal_Template.lean
+++ b/tests/lean/External/FunsExternal_Template.lean
@@ -6,12 +6,6 @@ import External.Types
 open Primitives
 open external
 
-/- [core::mem::swap]:
-   Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/mem/mod.rs', lines 726:0-726:42
-   Name pattern: core::mem::swap -/
-axiom core.mem.swap
-  (T : Type) : T → T → State → Result (State × (T × T))
-
 /- [core::num::nonzero::{core::num::nonzero::NonZeroU32#14}::new]:
    Source: '/rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/num/nonzero.rs', lines 79:16-79:57
    Name pattern: core::num::nonzero::{core::num::nonzero::NonZeroU32}::new -/