go/test/checkbce.go

// +build amd64
// errorcheck -0 -d=ssa/check_bce/debug=3

// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Test that the compiler does bounds check elimination as expected.
// This avoids accidental regressions.

package main

func f0(a []int) {
	a[0] = 1 // ERROR "Found IsInBounds$"
	a[0] = 1
	a[6] = 1 // ERROR "Found IsInBounds$"
	a[6] = 1
	a[5] = 1
	a[5] = 1
}

func f1(a [256]int, i int) {
	var j int
	useInt(a[i]) // ERROR "Found IsInBounds$"
	j = i % 256
	useInt(a[j]) // ERROR "Found IsInBounds$"
	j = i & 255
	useInt(a[j])
	j = i & 17
	useInt(a[j])

	if 4 <= i && i < len(a) {
		useInt(a[i])
		useInt(a[i-1]) // ERROR "Found IsInBounds$"
		// TODO: 'if 4 <= i && i < len(a)' gets rewritten to 'if uint(i - 4) < 256 - 4',
		// which the bounds checker cannot yet use to infer that the next line doesn't need a bounds check.
		useInt(a[i-4])
	}
}

func f2(a [256]int, i uint) {
	useInt(a[i]) // ERROR "Found IsInBounds$"
	j := i % 256
	useInt(a[j])
	j = i & 255
	useInt(a[j])
	j = i & 17
	useInt(a[j])
}

func f2a(a [35]int, i uint8) {
	useInt(a[i]) // ERROR "Found IsInBounds$"
	j := i & 34
	useInt(a[j])
	j = i & 17
	useInt(a[j])
}

func f2b(a [35]int, i uint16) {
	useInt(a[i]) // ERROR "Found IsInBounds$"
	j := i & 34
	useInt(a[j])
	j = i & 17
	useInt(a[j])
}

func f2c(a [35]int, i uint32) {
	useInt(a[i]) // ERROR "Found IsInBounds$"
	j := i & 34
	useInt(a[j])
	j = i & 17
	useInt(a[j])
}

func f3(a [256]int, i uint8) {
	useInt(a[i])
	useInt(a[i+10])
	useInt(a[i+14])
}

func f4(a [27]int, i uint8) {
	useInt(a[i%15])
	useInt(a[i%19])
	useInt(a[i%27])
}

func f5(a []int) {
	if len(a) > 5 {
		useInt(a[5])
		useSlice(a[6:])
		useSlice(a[:6])
	}
}

func f6(a [32]int, b [64]int, i int) {
	useInt(a[uint32(i*0x07C4ACDD)>>27])
	useInt(b[uint64(i*0x07C4ACDD)>>58])
	useInt(a[uint(i*0x07C4ACDD)>>59])

	// The following bounds should not be removed because they can overflow.
	useInt(a[uint32(i*0x106297f105d0cc86)>>26]) // ERROR "Found IsInBounds$"
	useInt(b[uint64(i*0x106297f105d0cc86)>>57]) // ERROR "Found IsInBounds$"
	useInt(a[int32(i*0x106297f105d0cc86)>>26])  // ERROR "Found IsInBounds$"
	useInt(b[int64(i*0x106297f105d0cc86)>>57])  // ERROR "Found IsInBounds$"
}

func g1(a []int) {
	for i := range a {
		a[i] = i
		useSlice(a[:i+1])
		useSlice(a[:i])
	}
}

func g2(a []int) {
	useInt(a[3]) // ERROR "Found IsInBounds$"
	useInt(a[2])
	useInt(a[1])
	useInt(a[0])
}

func g3(a []int) {
	for i := range a[:256] { // ERROR "Found IsSliceInBounds$"
		useInt(a[i]) // ERROR "Found IsInBounds$"
	}
	b := a[:256]
	for i := range b {
		useInt(b[i])
	}
}

func g4(a [100]int) {
	for i := 10; i < 50; i++ {
		useInt(a[i-10])
		useInt(a[i])
		useInt(a[i+25])
		useInt(a[i+50])

		// The following are out of bounds.
		useInt(a[i-11]) // ERROR "Found IsInBounds$"
		useInt(a[i+51]) // ERROR "Found IsInBounds$"
	}
}

func Uint64(b []byte) uint64 {
	_ = b[7] // ERROR "Found IsInBounds$"
	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
}

func decode1(data []byte) (x uint64) {
	for len(data) >= 32 {
		x += Uint64(data[:8])
		x += Uint64(data[8:16])
		x += Uint64(data[16:24])
		x += Uint64(data[24:32])
		data = data[32:]
	}
	return x
}

func decode2(data []byte) (x uint64) {
	// TODO(rasky): this should behave like decode1 and compile to no
	// boundchecks. We're currently not able to remove all of them.
	for len(data) >= 32 {
		x += Uint64(data)
		data = data[8:]
		x += Uint64(data) // ERROR "Found IsInBounds$"
		data = data[8:]
		x += Uint64(data) // ERROR "Found IsInBounds$"
		data = data[8:]
		x += Uint64(data) // ERROR "Found IsInBounds$"
		data = data[8:]
	}
	return x
}

//go:noinline
func useInt(a int) {
}

//go:noinline
func useSlice(a []int) {
}

func main() {
}