Revert "perf: bounds-check elimination in loop-indexed array access (#506)" (#511)

This reverts commit dcf1cd3.

Co-authored-by: cs01 <cs01@users.noreply.github.com>

Author: cs01

src/codegen/expressions/access/index.ts

@@ -38,7 +38,6 @@ export interface IndexAccessGeneratorContext {
   ensureDouble(value: string): string;
   setUsesJson(value: boolean): void;
   emitError(message: string, loc?: SourceLocation, suggestion?: string): never;
-  isSafeIndex(indexName: string, arrayName: string): boolean;
 }
 
 /**
@@ -182,19 +181,6 @@ export class IndexAccessGenerator {
     return indexValue;
   }
 
-  // Returns true when the given index access is a direct `arr[i]` pattern where
-  // the (i, arr) pair has been proven safe by loop analysis, so we can skip the
-  // runtime bounds check entirely.
-  private isProvenSafeAccess(expr: IndexAccessNode | IndexAccessAssignmentNode): boolean {
-    const obj = expr.object as ExprBase;
-    const idx = expr.index as ExprBase;
-    if (obj.type !== "variable") return false;
-    if (idx.type !== "variable") return false;
-    const arrName = (expr.object as VariableNode).name;
-    const idxName = (expr.index as VariableNode).name;
-    return this.ctx.isSafeIndex(idxName, arrName);
-  }
-
   private emitBoundsCheck(arrayPtr: string, arrayType: string, index: string): void {
     const lenPtr = this.ctx.nextTemp();
     this.ctx.emit(
@@ -232,9 +218,7 @@ export class IndexAccessGenerator {
       stringArrayPtr = cast;
     }
 
-    if (!this.isProvenSafeAccess(expr)) {
-      this.emitBoundsCheck(stringArrayPtr, "%StringArray", index);
-    }
+    this.emitBoundsCheck(stringArrayPtr, "%StringArray", index);
 
     const dataPtr = this.ctx.nextTemp();
     this.ctx.emit(
@@ -265,9 +249,7 @@ export class IndexAccessGenerator {
       arrayPtr = cast;
     }
 
-    if (!this.isProvenSafeAccess(expr)) {
-      this.emitBoundsCheck(arrayPtr, "%Array", index);
-    }
+    this.emitBoundsCheck(arrayPtr, "%Array", index);
 
     const dataPtr = this.ctx.nextTemp();
     this.ctx.emit(`${dataPtr} = getelementptr inbounds %Array, %Array* ${arrayPtr}, i32 0, i32 0`);
@@ -334,10 +316,9 @@ export class IndexAccessGenerator {
     const index = this.toI32Index(indexDouble);
     const contiguousStride = this.getContiguousStride(expr);
 
-    const safeAccess = this.isProvenSafeAccess(expr);
     const arrayType = this.ctx.getVariableType(arrayPtr);
     if (arrayType === "%ObjectArray*") {
-      if (!safeAccess) this.emitBoundsCheck(arrayPtr, "%ObjectArray", index);
+      this.emitBoundsCheck(arrayPtr, "%ObjectArray", index);
       if (contiguousStride > 0) {
         return this.emitContiguousElementPtr(arrayPtr, "%ObjectArray", index, contiguousStride);
       }
@@ -353,7 +334,7 @@ export class IndexAccessGenerator {
     if (arrayType === "i8*") {
       const arrayCast = this.ctx.nextTemp();
       this.ctx.emit(`${arrayCast} = bitcast i8* ${arrayPtr} to %ObjectArray*`);
-      if (!safeAccess) this.emitBoundsCheck(arrayCast, "%ObjectArray", index);
+      this.emitBoundsCheck(arrayCast, "%ObjectArray", index);
       if (contiguousStride > 0) {
         return this.emitContiguousElementPtr(arrayCast, "%ObjectArray", index, contiguousStride);
       }
@@ -366,7 +347,7 @@ export class IndexAccessGenerator {
       return this.emitPointerArrayElementPtr(data, index);
     }
 
-    if (!safeAccess) this.emitBoundsCheck(arrayPtr, "%ObjectArray", index);
+    this.emitBoundsCheck(arrayPtr, "%ObjectArray", index);
     if (contiguousStride > 0) {
       return this.emitContiguousElementPtr(arrayPtr, "%ObjectArray", index, contiguousStride);
     }
@@ -385,9 +366,7 @@ export class IndexAccessGenerator {
 
     const index = this.toI32Index(indexDouble);
 
-    if (!this.isProvenSafeAccess(expr)) {
-      this.emitBoundsCheck(arrayPtr, "%Uint8Array", index);
-    }
+    this.emitBoundsCheck(arrayPtr, "%Uint8Array", index);
 
     const dataFieldPtr = this.ctx.nextTemp();
     this.ctx.emit(

src/codegen/infrastructure/generator-context.ts

@@ -988,12 +988,6 @@ export interface IGeneratorContext {
   currentVarDeclKey: string | null;
   setCurrentVarDeclKey(key: string | null): void;
   getCurrentVarDeclKey(): string | null;
-
-  // Bounds-check elimination (perf) — IMPORTANT: keep at END of interface.
-  pushSafeIndexScope(): void;
-  popSafeIndexScope(): void;
-  addSafeIndex(indexName: string, arrayName: string): void;
-  isSafeIndex(indexName: string, arrayName: string): boolean;
 }
 
 /**
@@ -2318,12 +2312,4 @@ export class MockGeneratorContext implements IGeneratorContext {
   getCurrentVarDeclKey(): string | null {
     return this.currentVarDeclKey;
   }
-
-  // Bounds-check elimination stubs for MockGeneratorContext (no-ops).
-  pushSafeIndexScope(): void {}
-  popSafeIndexScope(): void {}
-  addSafeIndex(_indexName: string, _arrayName: string): void {}
-  isSafeIndex(_indexName: string, _arrayName: string): boolean {
-    return false;
-  }
 }

src/codegen/llvm-generator.ts

@@ -330,14 +330,6 @@ export class LLVMGenerator extends BaseGenerator implements IGeneratorContext {
   public usesGC: number = 0;
   public usesMathRandom: number = 0;
 
-  // Bounds-check elimination: parallel arrays tracking (indexVar, arrayVar) pairs
-  // that are proven safe within the currently active loop scope.
-  // Parallel arrays used instead of Map for self-hosting compatibility.
-  public safeIndexVars: string[] = [];
-  public safeIndexArrays: string[] = [];
-  // Per-loop-scope frame: each entry is how many pairs were added when that scope began.
-  public safeIndexFrames: number[] = [];
-
   public emitError(message: string, loc?: SourceLocation, suggestion?: string): never {
     this.diagnostics.error(message, loc, suggestion);
     const output = this.diagnostics.formatDiagnostic(
@@ -1685,39 +1677,6 @@ export class LLVMGenerator extends BaseGenerator implements IGeneratorContext {
     // LLVMGenerator-specific fields not in BaseGenerator
     this.stringBuilderSlen.clear();
     this.stringBuilderScap.clear();
-    this.safeIndexVars.length = 0;
-    this.safeIndexArrays.length = 0;
-    this.safeIndexFrames.length = 0;
-  }
-
-  // Push a new loop scope for bounds-check elimination tracking
-  pushSafeIndexScope(): void {
-    this.safeIndexFrames.push(this.safeIndexVars.length);
-  }
-
-  // Pop the most recent loop scope, removing any pairs added within it
-  popSafeIndexScope(): void {
-    if (this.safeIndexFrames.length === 0) return;
-    const frameStart = this.safeIndexFrames[this.safeIndexFrames.length - 1];
-    this.safeIndexFrames.pop();
-    this.safeIndexVars.length = frameStart;
-    this.safeIndexArrays.length = frameStart;
-  }
-
-  // Record that indexName indexing into arrayName is proven in-bounds
-  addSafeIndex(indexName: string, arrayName: string): void {
-    this.safeIndexVars.push(indexName);
-    this.safeIndexArrays.push(arrayName);
-  }
-
-  // Check whether indexName indexing arrayName is known safe in some enclosing loop scope
-  isSafeIndex(indexName: string, arrayName: string): boolean {
-    for (let i = this.safeIndexVars.length - 1; i >= 0; i--) {
-      if (this.safeIndexVars[i] === indexName && this.safeIndexArrays[i] === arrayName) {
-        return true;
-      }
-    }
-    return false;
   }
 
   getThisPointer(): string | null {

src/codegen/statements/control-flow.ts

@@ -32,7 +32,6 @@ import type { FieldInfo } from "../infrastructure/type-resolver/types.js";
 import { stripOptional } from "../infrastructure/type-system.js";
 import { setWantsI1 } from "../expressions/condition-generator.js";
 import { tryOptimizeWhileLoopMap } from "./loop-idiom.js";
-import { analyzeWhileSafety, analyzeForSafety } from "./loop-safety.js";
 
 interface ExprBase {
   type: string;
@@ -324,17 +323,7 @@ export class ControlFlowGenerator {
     this.ctx.setCurrentLabel(bodyLabel);
     this.loopContinueLabels.push(condLabel);
     this.loopBreakLabels.push(endLabel);
-
-    // Bounds-check elimination: if the loop matches a safe pattern, register
-    // the (indexVar, arrayVar) pair so arr[i] inside body skips its bounds check.
-    const whileSafePat = analyzeWhileSafety(whileStmt);
-    this.ctx.pushSafeIndexScope();
-    if (whileSafePat) {
-      this.ctx.addSafeIndex(whileSafePat.indexName, whileSafePat.arrayName);
-    }
-
     this.ctx.generateBlock(whileStmt.body, params);
-    this.ctx.popSafeIndexScope();
     this.loopContinueLabels.pop();
     this.loopBreakLabels.pop();
     const bodyHasTerminator = this.ctx.lastInstructionIsTerminator();
@@ -486,16 +475,7 @@ export class ControlFlowGenerator {
     this.ctx.setCurrentLabel(bodyLabel);
     this.loopContinueLabels.push(updateLabel);
     this.loopBreakLabels.push(endLabel);
-
-    // Bounds-check elimination: classic-for-loop safe index registration.
-    const forSafePat = analyzeForSafety(forStmt as ForStatement);
-    this.ctx.pushSafeIndexScope();
-    if (forSafePat) {
-      this.ctx.addSafeIndex(forSafePat.indexName, forSafePat.arrayName);
-    }
-
     this.ctx.generateBlock(forStmt.body, params);
-    this.ctx.popSafeIndexScope();
     this.loopContinueLabels.pop();
     this.loopBreakLabels.pop();
     const bodyHasTerminator3 = this.ctx.lastInstructionIsTerminator();