From 7def05274945cca10468538eca378af57568f830 Mon Sep 17 00:00:00 2001
From: Jakub Doka <jakub.doka2@gmail.com>
Date: Mon, 11 Nov 2024 21:55:18 +0100
Subject: [PATCH] preventing dangling nodes due to cycles in loop phys

---
 lang/README.md                             | 45 ++++++++++++++++++++++
 lang/src/son.rs                            | 19 ++++++---
 lang/tests/son_tests_very_nested_loops.txt |  6 +++
 3 files changed, 65 insertions(+), 5 deletions(-)
 create mode 100644 lang/tests/son_tests_very_nested_loops.txt

diff --git a/lang/README.md b/lang/README.md
index 695d936cd..f57453a52 100644
--- a/lang/README.md
+++ b/lang/README.md
@@ -615,6 +615,51 @@ main := fn(): uint {
 
 ### Purely Testing Examples
 
+#### very_nested_loops
+```hb
+$W := 200
+$H := 200
+$MAX_ITER := 20
+$ZOOM := 0.5
+
+main := fn(): int {
+	mv_x := 0.5
+	mv_y := 0.0
+
+	y := 0
+	loop if y < H break else {
+		x := 0
+		loop if x < W break else {
+			i := MAX_ITER - 1
+
+			c_i := (2.0 * @floatcast(@itf(@as(i32, @intcast(x)))) - @floatcast(@itf(@as(i32, @intcast(W))))) / (W * ZOOM) + mv_x
+			c_r := (2.0 * @floatcast(@itf(@as(i32, @intcast(y)))) - @floatcast(@itf(@as(i32, @intcast(H))))) / (H * ZOOM) + mv_y
+
+			z_i := c_i
+			z_r := c_r
+
+			// iteration
+			loop if (z_r + z_i) * (z_r + z_i) >= 4 | i == 0 break else {
+				// z = z * z + c
+				z_i = z_i * z_i + c_i
+				z_r = z_r * z_r + c_r
+				i -= 1
+			}
+			//   b g r
+			put_pixel(.(x, y), .(@as(u8, @intcast(i)), @as(u8, @intcast(i)), @as(u8, @intcast(i)), 255))
+		}
+	}
+
+	return 0
+}
+
+Color := struct {r: u8, g: u8, b: u8, a: u8}
+Vec := struct {x: uint, y: uint}
+
+put_pixel := fn(pos: Vec, color: Color): void {
+}
+```
+
 #### generic_type_mishap
 ```hb
 opaque := fn($Expr: type, ptr: ^?Expr): void {
diff --git a/lang/src/son.rs b/lang/src/son.rs
index cd8f68479..13f538f65 100644
--- a/lang/src/son.rs
+++ b/lang/src/son.rs
@@ -1298,14 +1298,21 @@ impl Nodes {
                 }
             }
             K::Loop => {
-                if self[target].inputs[0] == NEVER {
-                    return Some(NEVER);
-                }
-
-                if self[target].inputs[1] == NEVER {
+                if self[target].inputs[1] == NEVER || self[target].inputs[0] == NEVER {
                     self.lock(target);
                     for o in self[target].outputs.clone() {
                         if self[o].kind == Kind::Phi {
+                            self.remove_node_lookup(target);
+
+                            let prev = self[o].inputs[2];
+                            self[o].inputs[2] = VOID;
+                            self[VOID].outputs.push(o);
+                            let index = self[prev].outputs.iter().position(|&n| n == o).unwrap();
+                            self[prev].outputs.swap_remove(index);
+                            self.lock(o);
+                            self.remove(prev);
+                            self.unlock(o);
+
                             self.replace(o, self[o].inputs[1]);
                         }
                     }
@@ -3398,6 +3405,7 @@ impl<'a> Codegen<'a> {
                     ),
                     &mut self.ci.nodes,
                 );
+
                 self.ci.loops.push(Loop {
                     node: self.ci.ctrl.get(),
                     ctrl: [StrongRef::DEFAULT; 2],
@@ -4749,6 +4757,7 @@ mod tests {
         fb_driver;
 
         // Purely Testing Examples;
+        very_nested_loops;
         generic_type_mishap;
         storing_into_nullable_struct;
         scheduling_block_did_dirty;
diff --git a/lang/tests/son_tests_very_nested_loops.txt b/lang/tests/son_tests_very_nested_loops.txt
new file mode 100644
index 000000000..e10b42134
--- /dev/null
+++ b/lang/tests/son_tests_very_nested_loops.txt
@@ -0,0 +1,6 @@
+main:
+    LI64 r1, 0d
+    JALA r0, r31, 0a
+code size: 29
+ret: 0
+status: Ok(())