Method createLookupBoundsCheck

compiler/asserts.go:19–35

createLookupBoundsCheck emits a bounds check before doing a lookup into a slice. This is required by the Go language spec: an index out of bounds must cause a panic. The caller should make sure that index is at least as big as arrayLen.

(arrayLen, index llvm.Value)

// cause a panic.
// The caller should make sure that index is at least as big as arrayLen.
func (b *builder) createLookupBoundsCheck(arrayLen, index llvm.Value) {
	if b.info.nobounds {
		// The //go:nobounds pragma was added to the function to avoid bounds
		// checking.
		return
	}

	// Extend arrayLen if it's too small.
	if index.Type().IntTypeWidth() > arrayLen.Type().IntTypeWidth() {
		// The index is bigger than the array length type, so extend it.
		arrayLen = b.CreateZExt(arrayLen, index.Type(), "")
	}

	// Now do the bounds check: index >= arrayLen
	outOfBounds := b.CreateICmp(llvm.IntUGE, index, arrayLen, "")
	b.createRuntimeAssert(outOfBounds, "lookup", "lookupPanic")
}

// createSliceBoundsCheck emits a bounds check before a slicing operation to make
// sure it is within bounds.