[Fix] Control Dep Should Only Add To Defs

Control dep should only affect how things are invalidated, which are modeled as 
defs including declarations, writable uses to variables and expressions. 

Closes #633 

commit-id:41bd6fe5

compiler/forget/src/IR/FuncTopLevel.ts

@@ -77,7 +77,10 @@ export class FuncTopLevel {
   }
 
   /**
-   * All "uses" of {@link Val}.
+   * All usages.
+   * - all references to declarations, regardless of the ref kind.
+   * - all references to expressions.
+   * - all references to free variables (behind a flag).
    */
   get uses(): Ref<Val>[] {
     return [
@@ -88,16 +91,23 @@ export class FuncTopLevel {
   }
 
   /**
-   * All mutable uses. This needs to be lazy so it's computed after refinements.
+   * All usages that are considered potentially mutable (not readonly).
    */
   get mutableUses(): Ref<Val>[] {
     return this.uses.filter((use) => !use.immutable);
   }
 
   /**
-   * All defs. This needs to be lazy since it depends on {@link mutableUses}.
+   * All "defs".
+   * - all declarations
+   * - all expressions (yea they are immediately defined and referenced)
+   * - all mutable uses
    */
   get defs(): Val[] {
-    return [...this.decls, ...this.mutableUses.map((use) => use.val)];
+    return [
+      ...this.decls,
+      ...this.refsToExprs.map((use) => use.val),
+      ...this.mutableUses.map((use) => use.val),
+    ];
   }
 }

compiler/forget/src/MiddleEnd/DepGraphAnalysis.ts

@@ -132,8 +132,12 @@ function populateValGraph(valGraph: DepGraph.ValGraph, irFunc: IR.Func) {
     const basicBlock = cfg.blocks.get(blockId)!;
     basicBlock.parents.forEach((parent) => {
       for (const dep of controlDeps) {
-        for (const use of parent.uses) {
-          valGraph.getOrCreateVertex(use.val).addDependency(dep);
+        for (const val of parent.defs) {
+          invariant(
+            !IR.isInputVal(val),
+            "No inputs should be control dependent."
+          );
+          valGraph.getOrCreateVertex(val).addDependency(dep);
         }
       }
     });