All files / src/generator array-subscript.js

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// @flow
import opcode from '../emitter/opcode';
import mergeBlock from './merge-block';
import type { GeneratorType } from './flow/types';
import { TYPE_ARRAY } from '../semantics/metadata';
import mapSyntax from './map-syntax';
 
const generateArraySubscript: GeneratorType = (node, parent) => {
  const identifier = node.params[0];
  const isArray = identifier.meta[TYPE_ARRAY];
  const block = node.params.map(mapSyntax(parent)).reduce(mergeBlock, []);
  let type = node.type;
 
  if (isArray != null) {
    // For array types, the index is multiplied by the contained object size
    block.push.apply(block, [
      { kind: opcode.i32Const, params: [2] },
      { kind: opcode.i32Shl, params: [] },
    ]);
    type = isArray;
  }
 
  // The sequence of opcodes to perfrom a memory load is
  // get(Local|Global) base, i32Const offset[, i32Const size, i32Mul ], i32Add
  block.push({ kind: opcode.i32Add, params: [] });
 
  block.push({
    kind: opcode[String(type) + 'Load'],
    params: [
      // Alignment
      2,
      // Memory. Always 0 in the WASM MVP
      0,
    ],
  });
 
  return block;
};
 
export default generateArraySubscript;