From 8a4130dea3087ca8e528322bf7898f91c1043fce Mon Sep 17 00:00:00 2001
From: Marceline Cramer <cramermarceline@gmail.com>
Date: Fri, 24 Apr 2026 22:27:28 -0600
Subject: [PATCH] Add Salsa support to IR

---
 Cargo.lock           |  1 +
 crates/ir/Cargo.toml |  2 ++
 crates/ir/src/lib.rs | 47 ++++++++++++++++++++++++++++++++++++--------
 3 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index e6769f4..173b9e3 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -587,6 +587,7 @@ dependencies = [
  "arbitrary",
  "derive-where",
  "ordered-float",
+ "salsa",
  "serde",
 ]
 
diff --git a/crates/ir/Cargo.toml b/crates/ir/Cargo.toml
index e163821..1acc33e 100644
--- a/crates/ir/Cargo.toml
+++ b/crates/ir/Cargo.toml
@@ -11,9 +11,11 @@ rust-version.workspace = true
 arbitrary = { workspace = true, optional = true }
 derive-where = { workspace = true, features = ["serde"] }
 ordered-float.workspace = true
+salsa = { workspace = true, optional = true }
 serde = { workspace = true, optional = true }
 
 # TODO: test with feature power set
 [features]
 fuzz = ["dep:arbitrary", "ordered-float/arbitrary"]
+salsa = ["dep:salsa"]
 serde = ["dep:serde"]
diff --git a/crates/ir/src/lib.rs b/crates/ir/src/lib.rs
index af0bc72..423ebb9 100644
--- a/crates/ir/src/lib.rs
+++ b/crates/ir/src/lib.rs
@@ -31,13 +31,16 @@ use ordered_float::OrderedFloat;
 #[cfg(feature = "fuzz")]
 use arbitrary::Arbitrary;
 
+#[cfg(feature = "salsa")]
+use salsa::Update;
+
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
 // TODO: write more top-level docs
 // TODO: reintroduce validation logic
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -52,7 +55,7 @@ pub struct Program<T: ProgramInfo> {
     pub symbols: Vec<T::SymbolLabel>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -79,7 +82,7 @@ pub struct Relation<T: ProgramInfo> {
     pub rules: Vec<Rule<T>>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -95,7 +98,7 @@ pub struct Rule<T: ProgramInfo> {
     pub body: RuleBody<T>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -111,7 +114,7 @@ pub struct Assumption<T: ProgramInfo> {
     pub body: RuleBody<T>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -132,7 +135,7 @@ pub struct RuleBody<T: ProgramInfo> {
     pub body: Expr<T>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -142,7 +145,7 @@ pub struct Expr<T: ProgramInfo> {
     pub kind: ExprKind<T>,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive_where(Clone, Debug, PartialEq, Eq)]
 #[derive_where(PartialOrd, Ord; T: OrdProgramInfo)]
 #[derive_where(Hash; T: HashProgramInfo)]
 #[cfg_attr(feature = "fuzz", derive_where(Arbitrary; T: ArbitraryProgramInfo))]
@@ -314,7 +317,7 @@ impl Value {
 
 /// Associated types specializing a [Program] with stage-specific or format-specific information.
 // TODO: document how each type's usage changes based on stage and format
-pub trait ProgramInfo: Info {
+pub trait ProgramInfo {
     /// The type of global symbol labels.
     type SymbolLabel: Info;
 
@@ -339,6 +342,8 @@ pub trait ProgramInfo: Info {
 /// A blanket trait bounding all associated types in [ProgramInfo].
 pub trait Info: Clone + Debug + Eq {}
 
+impl<T: Clone + Debug + Eq> Info for T {}
+
 /// Creates a new trait to further bound the members of [ProgramInfo].
 macro_rules! def_bound_info {
     ($name:ident, $bounds:tt) => {
@@ -375,6 +380,32 @@ def_bound_info!(HashProgramInfo, Hash);
 #[cfg(feature = "fuzz")]
 def_bound_info!(ArbitraryProgramInfo, (for<'a> Arbitrary<'a>));
 
+#[cfg(feature = "salsa")]
+macro_rules! impl_update {
+    () => {};
+    ($head:ident, $($tail:ident),*) => {
+        impl_update!($head);
+        impl_update!($($tail),*);
+    };
+    ($item:ident) => {
+        unsafe impl<T: ProgramInfo> Update for $item<T> {
+            unsafe fn maybe_update(old: *mut Self, new: Self) -> bool {
+                let old: &mut Self = unsafe { &mut *old };
+
+                if *old == new {
+                    false
+                } else {
+                    let _ = std::mem::replace(old, new);
+                    true
+                }
+            }
+        }
+    };
+}
+
+#[cfg(feature = "salsa")]
+impl_update!(Program, Relation, Rule, RuleBody, Assumption, Expr, ExprKind);
+
 #[cfg(feature = "serde")]
 def_bound_info!(DeserializeProgramInfo, (for<'a> Deserialize<'a>));