From 326e8c13f777ca6583f11e1be39a3025eec08cf4 Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Thu, 16 Feb 2023 15:17:30 -0800
Subject: [PATCH] Scaffolding for LoadGlobal instruction

Adds a new `LoadGlobal` InstructionValue variant which will be used to represent
identifiers that refer to globals. We don't construct this value type yet.
---
 compiler/forget/src/HIR/HIR.ts                                | 1 +
 compiler/forget/src/HIR/PrintHIR.ts                           | 4 ++++
 compiler/forget/src/HIR/visitors.ts                           | 2 ++
 compiler/forget/src/Inference/InferReferenceEffects.ts        | 1 +
 compiler/forget/src/Optimization/DeadCodeElimination.ts       | 1 +
 compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts | 4 ++++
 .../forget/src/ReactiveScopes/InferReactiveScopeVariables.ts  | 1 +
 7 files changed, 14 insertions(+)

diff --git a/compiler/forget/src/HIR/HIR.ts b/compiler/forget/src/HIR/HIR.ts
index d6abb1cf8e..2733601827 100644
--- a/compiler/forget/src/HIR/HIR.ts
+++ b/compiler/forget/src/HIR/HIR.ts
@@ -442,6 +442,7 @@ export type InstructionData =
   | { kind: "ComputedStore"; object: Place; property: Place; value: Place }
   // load `object[index]` - like PropertyLoad but with a dynamic property
   | { kind: "ComputedLoad"; object: Place; property: Place }
+  | { kind: "LoadGlobal"; name: string }
   | FunctionExpression
   | {
       kind: "TaggedTemplateExpression";
diff --git a/compiler/forget/src/HIR/PrintHIR.ts b/compiler/forget/src/HIR/PrintHIR.ts
index 05164b718c..a34d79bc35 100644
--- a/compiler/forget/src/HIR/PrintHIR.ts
+++ b/compiler/forget/src/HIR/PrintHIR.ts
@@ -381,6 +381,10 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
       value += instrValue.quasis.at(-1)!.raw + "`";
       break;
     }
+    case "LoadGlobal": {
+      value = `Global ${instrValue.name}`;
+      break;
+    }
     default: {
       assertExhaustive(
         instrValue,
diff --git a/compiler/forget/src/HIR/visitors.ts b/compiler/forget/src/HIR/visitors.ts
index 0d376e66fc..edad1e8ca6 100644
--- a/compiler/forget/src/HIR/visitors.ts
+++ b/compiler/forget/src/HIR/visitors.ts
@@ -131,6 +131,7 @@ export function* eachInstructionValueOperand(
       yield* instrValue.subexprs;
       break;
     }
+    case "LoadGlobal":
     case "UnsupportedNode":
     case "Primitive":
     case "JSXText": {
@@ -259,6 +260,7 @@ export function mapInstructionOperands(
       instrValue.subexprs = instrValue.subexprs.map(fn);
       break;
     }
+    case "LoadGlobal":
     case "UnsupportedNode":
     case "Primitive":
     case "JSXText": {
diff --git a/compiler/forget/src/Inference/InferReferenceEffects.ts b/compiler/forget/src/Inference/InferReferenceEffects.ts
index c239f1a389..93d3fce9ca 100644
--- a/compiler/forget/src/Inference/InferReferenceEffects.ts
+++ b/compiler/forget/src/Inference/InferReferenceEffects.ts
@@ -640,6 +640,7 @@ function inferBlock(
         effectKind = Effect.Read;
         break;
       }
+      case "LoadGlobal":
       case "JSXText":
       case "Primitive": {
         valueKind = ValueKind.Immutable;
diff --git a/compiler/forget/src/Optimization/DeadCodeElimination.ts b/compiler/forget/src/Optimization/DeadCodeElimination.ts
index 41af43e617..1addf063f7 100644
--- a/compiler/forget/src/Optimization/DeadCodeElimination.ts
+++ b/compiler/forget/src/Optimization/DeadCodeElimination.ts
@@ -94,6 +94,7 @@ function pruneableValue(value: InstructionValue): boolean {
       // Potentially safe to prune, since they should just be creating new values
       return false;
     }
+    case "LoadGlobal":
     case "ArrayExpression":
     case "BinaryExpression":
     case "ComputedLoad":
diff --git a/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts b/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts
index 47ade2dbeb..2705d39233 100644
--- a/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts
+++ b/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts
@@ -788,6 +788,10 @@ function codegenInstructionValue(
       );
       break;
     }
+    case "LoadGlobal": {
+      value = t.identifier(instrValue.name);
+      break;
+    }
     default: {
       assertExhaustive(
         instrValue,
diff --git a/compiler/forget/src/ReactiveScopes/InferReactiveScopeVariables.ts b/compiler/forget/src/ReactiveScopes/InferReactiveScopeVariables.ts
index 1c7a5d5acf..9c67fe1506 100644
--- a/compiler/forget/src/ReactiveScopes/InferReactiveScopeVariables.ts
+++ b/compiler/forget/src/ReactiveScopes/InferReactiveScopeVariables.ts
@@ -168,6 +168,7 @@ function isMutable({ id }: Instruction, place: Place): boolean {
 
 function mayAllocate(value: InstructionValue): boolean {
   switch (value.kind) {
+    case "LoadGlobal":
     case "TypeCastExpression":
     case "BinaryExpression":
     case "Identifier":