very basic const propagation possible

rust2/src/lib.rs

@@ -86,7 +86,7 @@ where
     if let Some(DumpKind::Mir) = config.dump {
         let mir_alloc = Bump::new();
         let mir = mir::optimized_mir(&mir_alloc, &optimized_hir);
-        println!("{mir:#?}");
+        //println!("{mir:#?}");
     }
 
     let cg_alloc = Bump::new();

rust2/src/main.rs

@@ -16,6 +16,7 @@ fn main() {
 
     tracing_subscriber::fmt()
         .with_env_filter(tracing_subscriber::filter::EnvFilter::from_default_env())
+        .without_time()
         .init();
 
     let src = fs::read_to_string(&args.file).unwrap_or_else(|err| {

rust2/src/mir/mod.rs

@@ -54,10 +54,10 @@ enum StmtKind<'mir> {
     SetN(u8, Store),
 }
 
-#[tracing::instrument]
+#[tracing::instrument(skip(alloc, hir))]
 pub fn optimized_mir<'mir>(alloc: &'mir Bump, hir: &Hir<'_>) -> Mir<'mir> {
     let mut mir = hir_to_mir(alloc, hir);
-    opts::pass_get_state_info(alloc, &mut mir);
+    opts::passes(alloc, &mut mir);
     mir
 }
 

rust2/src/mir/opts.rs

@@ -1,4 +1,5 @@
 use bumpalo::Bump;
+use tracing::info;
 
 use crate::mir::{
     state::{CellState, MemoryState, MemoryStateChange},
@@ -6,13 +7,19 @@ use crate::mir::{
 };
 
 /// this pass fills out as much state info for all statements as possible
-#[tracing::instrument]
+#[tracing::instrument(skip(alloc, mir))]
+pub fn passes<'mir>(alloc: &'mir Bump, mir: &mut Mir<'mir>) {
+    pass_get_state_info(alloc, mir);
+    pass_const_propagation(mir);
+}
+/// this pass fills out as much state info for all statements as possible
+#[tracing::instrument(skip(alloc, mir))]
 pub fn pass_get_state_info<'mir>(alloc: &'mir Bump, mir: &mut Mir<'mir>) {
     let empty_state = MemoryState::empty(alloc);
     pass_get_state_info_inner(alloc, mir, empty_state);
 }
 
-#[tracing::instrument]
+#[tracing::instrument(skip(alloc, mir))]
 fn pass_get_state_info_inner<'mir>(
     alloc: &'mir Bump,
     mir: &mut Mir<'mir>,
@@ -85,5 +92,28 @@ fn pass_get_state_info_inner<'mir>(
     }
 }
 
-#[tracing::instrument]
+#[tracing::instrument(skip(mir))]
-fn pass_const_propagation(mir: &mut Mir<'_>) {}
+fn pass_const_propagation(mir: &mut Mir<'_>) {
+    pass_const_propagation_inner(mir)
+}
+
+fn pass_const_propagation_inner(mir: &mut Mir<'_>) {
+    for stmt in &mut mir.stmts {
+        match &mut stmt.kind {
+            StmtKind::Out => {
+                let state = stmt.state.state_for_offset(0);
+                info!(?state, "We got the state of the output 😳😳😳");
+                // we could now insert a `SetN` before the `Out`, to mark the previous store
+                // as dead.
+            }
+            StmtKind::Loop(body) => {
+                let state = stmt.state.state_for_offset(0);
+                info!(?state, "We got the state of the output 😳😳😳");
+                // we could now insert a `SetN` before the `Out`, to mark the previous store
+                // as dead.
+                pass_const_propagation_inner(body);
+            }
+            _ => {}
+        }
+    }
+}

rust2/src/mir/state.rs

@@ -38,7 +38,7 @@ impl<'mir> MemoryState<'mir> {
         })))
     }
 
-    pub fn state_for_offset(&self, offset: i32) -> &'mir CellState {
+    pub fn state_for_offset(&self, offset: i32) -> CellState {
         self.0.borrow().state_for_offset(offset)
     }
 }
@@ -60,26 +60,25 @@ pub struct MemoryStateInner<'mir> {
 }
 
 impl<'mir> MemoryStateInner<'mir> {
-    pub fn state_for_offset(&self, offset: i32) -> &'mir CellState {
+    pub fn state_for_offset(&self, offset: i32) -> CellState {
         let mut offset = offset;
         for delta in &self.deltas {
             match delta {
                 MemoryStateChange::Change {
                     offset: write_offset,
                     new_state,
-                } if *write_offset == offset => {
+                } if *write_offset == offset => return new_state.clone(),
-                    return new_state;
-                }
                 MemoryStateChange::Move(change) => offset -= change,
                 // we may not access the forbidden knowledge
-                MemoryStateChange::Forget => return &CellState::Unknown,
+                MemoryStateChange::Forget => return CellState::Unknown,
                 _ => {}
             }
         }
 
         self.prev
+            .as_ref()
             .map(|state| state.state_for_offset(offset))
-            .unwrap_or(&CellState::Unknown)
+            .unwrap_or(CellState::Unknown)
     }
 }
 

rust2/test.bf

@@ -1 +1 @@
-+>.
+[-]+>[-]<<>.