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fix: handle negative indices in array slice #131

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Merged
cs01 merged 1 commit into from
Mar 9, 2026
Merged

fix: handle negative indices in array slice #131

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53 changes: 39 additions & 14 deletions src/codegen/types/collections/array/combine.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -574,6 +574,21 @@ function generateStringArrayJoin(
// slice
// ============================================

function normalizeSliceIndex(gen: IGeneratorContext, rawI32: string, length: string): string {
const isNeg = gen.emitIcmp("slt", "i32", rawI32, "0");
const adjusted = gen.nextTemp();
gen.emit(`${adjusted} = add i32 ${length}, ${rawI32}`);
const selected = gen.nextTemp();
gen.emit(`${selected} = select i1 ${isNeg}, i32 ${adjusted}, i32 ${rawI32}`);
const tooSmall = gen.emitIcmp("slt", "i32", selected, "0");
const clamped = gen.nextTemp();
gen.emit(`${clamped} = select i1 ${tooSmall}, i32 0, i32 ${selected}`);
const tooBig = gen.emitIcmp("sgt", "i32", clamped, length);
const final = gen.nextTemp();
gen.emit(`${final} = select i1 ${tooBig}, i32 ${length}, i32 ${clamped}`);
return final;
}

export function generateArraySlice(
gen: IGeneratorContext,
expr: MethodCallNode,
Expand Down Expand Up @@ -616,20 +631,25 @@ export function generateArraySlice(
if (expr.args.length >= 1) {
const startDouble = gen.generateExpression(expr.args[0], params);
const dblStart = gen.ensureDouble(startDouble);
startI32 = gen.nextTemp();
gen.emit(`${startI32} = fptosi double ${dblStart} to i32`);
const rawStart = gen.nextTemp();
gen.emit(`${rawStart} = fptosi double ${dblStart} to i32`);
startI32 = normalizeSliceIndex(gen, rawStart, length);
}

let endI32 = length;
if (expr.args.length >= 2) {
const endDouble = gen.generateExpression(expr.args[1], params);
const dblEnd = gen.ensureDouble(endDouble);
endI32 = gen.nextTemp();
gen.emit(`${endI32} = fptosi double ${dblEnd} to i32`);
const rawEnd = gen.nextTemp();
gen.emit(`${rawEnd} = fptosi double ${dblEnd} to i32`);
endI32 = normalizeSliceIndex(gen, rawEnd, length);
}

const sliceLen = gen.nextTemp();
gen.emit(`${sliceLen} = sub i32 ${endI32}, ${startI32}`);
const lenIsNeg = gen.emitIcmp("slt", "i32", sliceLen, "0");
const finalSliceLen = gen.nextTemp();
gen.emit(`${finalSliceLen} = select i1 ${lenIsNeg}, i32 0, i32 ${sliceLen}`);

const sizePtr = gen.nextTemp();
gen.emit(`${sizePtr} = getelementptr %Array, %Array* null, i32 1`);
Expand All @@ -639,7 +659,7 @@ export function generateArraySlice(
const newArrayPtr = gen.emitBitcast(arrayMem, "i8*", "%Array*");

const sliceLenI64 = gen.nextTemp();
gen.emit(`${sliceLenI64} = zext i32 ${sliceLen} to i64`);
gen.emit(`${sliceLenI64} = zext i32 ${finalSliceLen} to i64`);
const dataSize = gen.nextTemp();
gen.emit(`${dataSize} = mul i64 ${sliceLenI64}, 8`);
const dataMem = gen.emitCall("i8*", "@GC_malloc_atomic", `i64 ${dataSize}`);
Expand All @@ -659,11 +679,11 @@ export function generateArraySlice(

const newLenField = gen.nextTemp();
gen.emit(`${newLenField} = getelementptr inbounds %Array, %Array* ${newArrayPtr}, i32 0, i32 1`);
gen.emitStore("i32", sliceLen, newLenField);
gen.emitStore("i32", finalSliceLen, newLenField);

const newCapField = gen.nextTemp();
gen.emit(`${newCapField} = getelementptr inbounds %Array, %Array* ${newArrayPtr}, i32 0, i32 2`);
gen.emitStore("i32", sliceLen, newCapField);
gen.emitStore("i32", finalSliceLen, newCapField);

gen.setVariableType(newArrayPtr, "%Array*");
return newArrayPtr;
Expand Down Expand Up @@ -697,20 +717,25 @@ function generateStringArraySlice(
if (expr.args.length >= 1) {
const startDouble = gen.generateExpression(expr.args[0], params);
const dblStart = gen.ensureDouble(startDouble);
startI32 = gen.nextTemp();
gen.emit(`${startI32} = fptosi double ${dblStart} to i32`);
const rawStart = gen.nextTemp();
gen.emit(`${rawStart} = fptosi double ${dblStart} to i32`);
startI32 = normalizeSliceIndex(gen, rawStart, length);
}

let endI32 = length;
if (expr.args.length >= 2) {
const endDouble = gen.generateExpression(expr.args[1], params);
const dblEnd = gen.ensureDouble(endDouble);
endI32 = gen.nextTemp();
gen.emit(`${endI32} = fptosi double ${dblEnd} to i32`);
const rawEnd = gen.nextTemp();
gen.emit(`${rawEnd} = fptosi double ${dblEnd} to i32`);
endI32 = normalizeSliceIndex(gen, rawEnd, length);
}

const sliceLen = gen.nextTemp();
gen.emit(`${sliceLen} = sub i32 ${endI32}, ${startI32}`);
const lenIsNeg = gen.emitIcmp("slt", "i32", sliceLen, "0");
const finalSliceLen = gen.nextTemp();
gen.emit(`${finalSliceLen} = select i1 ${lenIsNeg}, i32 0, i32 ${sliceLen}`);

const sizePtr = gen.nextTemp();
gen.emit(`${sizePtr} = getelementptr ${arrType}, ${arrType}* null, i32 1`);
Expand All @@ -720,7 +745,7 @@ function generateStringArraySlice(
const newArrayPtr = gen.emitBitcast(arrayMem, "i8*", `${arrType}*`);

const sliceLenI64 = gen.nextTemp();
gen.emit(`${sliceLenI64} = zext i32 ${sliceLen} to i64`);
gen.emit(`${sliceLenI64} = zext i32 ${finalSliceLen} to i64`);
const dataSize = gen.nextTemp();
gen.emit(`${dataSize} = mul i64 ${sliceLenI64}, 8`);
const dataMem = gen.emitCall("i8*", "@GC_malloc", `i64 ${dataSize}`);
Expand Down Expand Up @@ -749,13 +774,13 @@ function generateStringArraySlice(
gen.emit(
`${newLenField} = getelementptr inbounds ${arrType}, ${arrType}* ${newArrayPtr}, i32 0, i32 1`,
);
gen.emitStore("i32", sliceLen, newLenField);
gen.emitStore("i32", finalSliceLen, newLenField);

const newCapField = gen.nextTemp();
gen.emit(
`${newCapField} = getelementptr inbounds ${arrType}, ${arrType}* ${newArrayPtr}, i32 0, i32 2`,
);
gen.emitStore("i32", sliceLen, newCapField);
gen.emitStore("i32", finalSliceLen, newCapField);

gen.setVariableType(newArrayPtr, `${arrType}*`);
return newArrayPtr;
Expand Down
34 changes: 34 additions & 0 deletions tests/fixtures/arrays/array-slice-negative.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
const nums: number[] = [10, 20, 30, 40, 50];
const last2 = nums.slice(-2);
const allButLast = nums.slice(0, -1);
const middle = nums.slice(1, -1);

let passed = true;

if (last2.length !== 2) passed = false;
if (last2[0] !== 40) passed = false;
if (last2[1] !== 50) passed = false;

if (allButLast.length !== 4) passed = false;
if (allButLast[0] !== 10) passed = false;
if (allButLast[3] !== 40) passed = false;

if (middle.length !== 3) passed = false;
if (middle[0] !== 20) passed = false;
if (middle[2] !== 40) passed = false;

const strs: string[] = ["a", "b", "c", "d", "e"];
const strLast2 = strs.slice(-2);
const strAllButLast = strs.slice(0, -1);

if (strLast2.length !== 2) passed = false;
if (strLast2[0] !== "d") passed = false;
if (strLast2[1] !== "e") passed = false;

if (strAllButLast.length !== 4) passed = false;
if (strAllButLast[0] !== "a") passed = false;
if (strAllButLast[3] !== "d") passed = false;

if (passed) {
console.log("TEST_PASSED");
}
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