mirror of
https://github.com/golang/go
synced 2024-11-24 08:50:14 -07:00
e0d37a33ab
When a loop has bound len(s)-delta, findIndVar detected it and
returned len(s) as (conservative) upper bound. This little lie
allowed loopbce to drop bound checks.
It is obviously more generic to teach prove about relations like
x+d<w for non-constant "w"; we already handled the case for
constant "w", so we just want to learn that if d<0, then x+d<w
proves that x<w.
To be able to remove the code from findIndVar, we also need
to teach prove that len() and cap() are always non-negative.
This CL allows to prove 633 more checks in cmd+std. Most
of them are cases where the code was already testing before
accessing a slice but the compiler didn't know it. For instance,
take strings.HasSuffix:
func HasSuffix(s, suffix string) bool {
return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
}
When suffix is a literal string, the compiler now understands
that the explicit check is enough to not emit a slice check.
I also found a loopbce test that was incorrectly
written to detect an overflow but had a off-by-one (on the
conservative side), so it unexpectly passed with this CL; I
changed it to really trigger the overflow as intended.
Change-Id: Ib5abade337db46b8811425afebad4719b6e46c4a
Reviewed-on: https://go-review.googlesource.com/105635
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
661 lines
11 KiB
Go
661 lines
11 KiB
Go
// +build amd64
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// errorcheck -0 -d=ssa/prove/debug=1
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// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "math"
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func f0(a []int) int {
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a[0] = 1
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a[0] = 1 // ERROR "Proved IsInBounds$"
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a[6] = 1
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a[6] = 1 // ERROR "Proved IsInBounds$"
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a[5] = 1 // ERROR "Proved IsInBounds$"
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a[5] = 1 // ERROR "Proved IsInBounds$"
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return 13
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}
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func f1(a []int) int {
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if len(a) <= 5 {
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return 18
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}
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a[0] = 1 // ERROR "Proved IsInBounds$"
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a[0] = 1 // ERROR "Proved IsInBounds$"
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a[6] = 1
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a[6] = 1 // ERROR "Proved IsInBounds$"
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a[5] = 1 // ERROR "Proved IsInBounds$"
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a[5] = 1 // ERROR "Proved IsInBounds$"
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return 26
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}
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func f1b(a []int, i int, j uint) int {
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if i >= 0 && i < len(a) {
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return a[i] // ERROR "Proved IsInBounds$"
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}
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if i >= 10 && i < len(a) {
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return a[i] // ERROR "Proved IsInBounds$"
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}
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if i >= 10 && i < len(a) {
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return a[i] // ERROR "Proved IsInBounds$"
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}
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if i >= 10 && i < len(a) {
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return a[i-10] // ERROR "Proved IsInBounds$"
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}
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if j < uint(len(a)) {
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return a[j] // ERROR "Proved IsInBounds$"
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}
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return 0
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}
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func f1c(a []int, i int64) int {
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c := uint64(math.MaxInt64 + 10) // overflows int
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d := int64(c)
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if i >= d && i < int64(len(a)) {
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// d overflows, should not be handled.
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return a[i]
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}
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return 0
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}
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func f2(a []int) int {
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for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1"
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a[i+1] = i
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a[i+1] = i // ERROR "Proved IsInBounds$"
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}
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return 34
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}
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func f3(a []uint) int {
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for i := uint(0); i < uint(len(a)); i++ {
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a[i] = i // ERROR "Proved IsInBounds$"
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}
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return 41
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}
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func f4a(a, b, c int) int {
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if a < b {
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if a == b { // ERROR "Disproved Eq64$"
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return 47
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}
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if a > b { // ERROR "Disproved Greater64$"
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return 50
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}
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if a < b { // ERROR "Proved Less64$"
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return 53
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}
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// We can't get to this point and prove knows that, so
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// there's no message for the next (obvious) branch.
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if a != a {
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return 56
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}
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return 61
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}
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return 63
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}
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func f4b(a, b, c int) int {
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if a <= b {
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if a >= b {
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if a == b { // ERROR "Proved Eq64$"
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return 70
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}
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return 75
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}
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return 77
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}
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return 79
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}
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func f4c(a, b, c int) int {
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if a <= b {
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if a >= b {
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if a != b { // ERROR "Disproved Neq64$"
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return 73
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}
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return 75
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}
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return 77
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}
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return 79
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}
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func f4d(a, b, c int) int {
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if a < b {
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if a < c {
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if a < b { // ERROR "Proved Less64$"
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if a < c { // ERROR "Proved Less64$"
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return 87
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}
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return 89
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}
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return 91
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}
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return 93
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}
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return 95
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}
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func f4e(a, b, c int) int {
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if a < b {
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if b > a { // ERROR "Proved Greater64$"
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return 101
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}
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return 103
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}
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return 105
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}
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func f4f(a, b, c int) int {
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if a <= b {
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if b > a {
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if b == a { // ERROR "Disproved Eq64$"
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return 112
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}
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return 114
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}
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if b >= a { // ERROR "Proved Geq64$"
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if b == a { // ERROR "Proved Eq64$"
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return 118
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}
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return 120
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}
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return 122
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}
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return 124
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}
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func f5(a, b uint) int {
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if a == b {
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if a <= b { // ERROR "Proved Leq64U$"
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return 130
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}
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return 132
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}
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return 134
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}
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// These comparisons are compile time constants.
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func f6a(a uint8) int {
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if a < a { // ERROR "Disproved Less8U$"
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return 140
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}
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return 151
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}
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func f6b(a uint8) int {
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if a < a { // ERROR "Disproved Less8U$"
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return 140
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}
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return 151
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}
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func f6x(a uint8) int {
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if a > a { // ERROR "Disproved Greater8U$"
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return 143
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}
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return 151
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}
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func f6d(a uint8) int {
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if a <= a { // ERROR "Proved Leq8U$"
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return 146
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}
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return 151
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}
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func f6e(a uint8) int {
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if a >= a { // ERROR "Proved Geq8U$"
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return 149
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}
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return 151
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}
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func f7(a []int, b int) int {
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if b < len(a) {
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a[b] = 3
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if b < len(a) { // ERROR "Proved Less64$"
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a[b] = 5 // ERROR "Proved IsInBounds$"
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}
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}
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return 161
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}
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func f8(a, b uint) int {
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if a == b {
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return 166
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}
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if a > b {
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return 169
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}
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if a < b { // ERROR "Proved Less64U$"
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return 172
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}
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return 174
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}
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func f9(a, b bool) int {
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if a {
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return 1
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}
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if a || b { // ERROR "Disproved Arg$"
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return 2
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}
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return 3
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}
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func f10(a string) int {
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n := len(a)
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// We optimize comparisons with small constant strings (see cmd/compile/internal/gc/walk.go),
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// so this string literal must be long.
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if a[:n>>1] == "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" {
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return 0
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}
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return 1
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}
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func f11a(a []int, i int) {
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useInt(a[i])
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useInt(a[i]) // ERROR "Proved IsInBounds$"
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}
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func f11b(a []int, i int) {
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useSlice(a[i:])
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useSlice(a[i:]) // ERROR "Proved IsSliceInBounds$"
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}
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func f11c(a []int, i int) {
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useSlice(a[:i])
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useSlice(a[:i]) // ERROR "Proved IsSliceInBounds$"
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}
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func f11d(a []int, i int) {
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useInt(a[2*i+7])
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useInt(a[2*i+7]) // ERROR "Proved IsInBounds$"
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}
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func f12(a []int, b int) {
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useSlice(a[:b])
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}
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func f13a(a, b, c int, x bool) int {
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if a > 12 {
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if x {
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if a < 12 { // ERROR "Disproved Less64$"
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return 1
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}
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}
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if x {
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if a <= 12 { // ERROR "Disproved Leq64$"
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return 2
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}
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}
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if x {
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if a == 12 { // ERROR "Disproved Eq64$"
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return 3
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}
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}
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if x {
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if a >= 12 { // ERROR "Proved Geq64$"
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return 4
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}
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}
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if x {
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if a > 12 { // ERROR "Proved Greater64$"
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return 5
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}
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}
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return 6
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}
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return 0
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}
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func f13b(a int, x bool) int {
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if a == -9 {
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if x {
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if a < -9 { // ERROR "Disproved Less64$"
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return 7
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}
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}
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if x {
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if a <= -9 { // ERROR "Proved Leq64$"
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return 8
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}
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}
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if x {
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if a == -9 { // ERROR "Proved Eq64$"
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return 9
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}
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}
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if x {
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if a >= -9 { // ERROR "Proved Geq64$"
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return 10
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}
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}
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if x {
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if a > -9 { // ERROR "Disproved Greater64$"
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return 11
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}
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}
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return 12
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}
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return 0
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}
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func f13c(a int, x bool) int {
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if a < 90 {
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if x {
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if a < 90 { // ERROR "Proved Less64$"
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return 13
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}
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}
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if x {
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if a <= 90 { // ERROR "Proved Leq64$"
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return 14
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}
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}
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if x {
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if a == 90 { // ERROR "Disproved Eq64$"
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return 15
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}
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}
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if x {
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if a >= 90 { // ERROR "Disproved Geq64$"
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return 16
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}
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}
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if x {
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if a > 90 { // ERROR "Disproved Greater64$"
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return 17
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}
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}
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return 18
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}
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return 0
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}
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func f13d(a int) int {
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if a < 5 {
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if a < 9 { // ERROR "Proved Less64$"
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return 1
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}
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}
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return 0
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}
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func f13e(a int) int {
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if a > 9 {
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if a > 5 { // ERROR "Proved Greater64$"
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return 1
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}
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}
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return 0
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}
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func f13f(a int64) int64 {
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if a > math.MaxInt64 {
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if a == 0 { // ERROR "Disproved Eq64$"
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return 1
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}
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}
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return 0
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}
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func f13g(a int) int {
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if a < 3 {
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return 5
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}
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if a > 3 {
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return 6
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}
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if a == 3 { // ERROR "Proved Eq64$"
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return 7
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}
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return 8
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}
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func f13h(a int) int {
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if a < 3 {
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if a > 1 {
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if a == 2 { // ERROR "Proved Eq64$"
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return 5
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}
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}
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}
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return 0
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}
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func f13i(a uint) int {
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if a == 0 {
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return 1
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}
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if a > 0 { // ERROR "Proved Greater64U$"
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return 2
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}
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return 3
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}
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func f14(p, q *int, a []int) {
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// This crazy ordering usually gives i1 the lowest value ID,
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// j the middle value ID, and i2 the highest value ID.
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// That used to confuse CSE because it ordered the args
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// of the two + ops below differently.
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// That in turn foiled bounds check elimination.
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i1 := *p
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j := *q
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i2 := *p
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useInt(a[i1+j])
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useInt(a[i2+j]) // ERROR "Proved IsInBounds$"
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}
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func f15(s []int, x int) {
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useSlice(s[x:])
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useSlice(s[:x]) // ERROR "Proved IsSliceInBounds$"
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}
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func f16(s []int) []int {
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if len(s) >= 10 {
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return s[:10] // ERROR "Proved IsSliceInBounds$"
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}
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return nil
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}
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func f17(b []int) {
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for i := 0; i < len(b); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1"
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// This tests for i <= cap, which we can only prove
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// using the derived relation between len and cap.
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// This depends on finding the contradiction, since we
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// don't query this condition directly.
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useSlice(b[:i]) // ERROR "Proved IsSliceInBounds$"
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}
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}
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func f18(b []int, x int, y uint) {
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_ = b[x]
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_ = b[y]
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if x > len(b) { // ERROR "Disproved Greater64$"
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return
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}
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if y > uint(len(b)) { // ERROR "Disproved Greater64U$"
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return
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}
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if int(y) > len(b) { // ERROR "Disproved Greater64$"
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return
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}
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}
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func sm1(b []int, x int) {
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// Test constant argument to slicemask.
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useSlice(b[2:8]) // ERROR "Proved slicemask not needed$"
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// Test non-constant argument with known limits.
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if cap(b) > 10 {
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useSlice(b[2:]) // ERROR "Proved slicemask not needed$"
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}
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}
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func lim1(x, y, z int) {
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// Test relations between signed and unsigned limits.
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if x > 5 {
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if uint(x) > 5 { // ERROR "Proved Greater64U$"
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return
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}
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}
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if y >= 0 && y < 4 {
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if uint(y) > 4 { // ERROR "Disproved Greater64U$"
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return
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}
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if uint(y) < 5 { // ERROR "Proved Less64U$"
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return
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}
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}
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if z < 4 {
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if uint(z) > 4 { // Not provable without disjunctions.
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return
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}
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}
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}
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// fence1–4 correspond to the four fence-post implications.
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func fence1(b []int, x, y int) {
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// Test proofs that rely on fence-post implications.
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if x+1 > y {
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if x < y { // ERROR "Disproved Less64$"
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return
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}
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}
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if len(b) < cap(b) {
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// This eliminates the growslice path.
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b = append(b, 1) // ERROR "Disproved Greater64$"
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}
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}
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func fence2(x, y int) {
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if x-1 < y {
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if x > y { // ERROR "Disproved Greater64$"
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return
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}
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}
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}
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func fence3(b []int, x, y int64) {
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if x-1 >= y {
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if x <= y { // Can't prove because x may have wrapped.
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return
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}
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}
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if x != math.MinInt64 && x-1 >= y {
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if x <= y { // ERROR "Disproved Leq64$"
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return
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}
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}
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if n := len(b); n > 0 {
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b[n-1] = 0 // ERROR "Proved IsInBounds$"
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}
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}
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func fence4(x, y int64) {
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if x >= y+1 {
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if x <= y {
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return
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}
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}
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if y != math.MaxInt64 && x >= y+1 {
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if x <= y { // ERROR "Disproved Leq64$"
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return
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}
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}
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}
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// Check transitive relations
|
||
func trans1(x, y int64) {
|
||
if x > 5 {
|
||
if y > x {
|
||
if y > 2 { // ERROR "Proved Greater64"
|
||
return
|
||
}
|
||
} else if y == x {
|
||
if y > 5 { // ERROR "Proved Greater64"
|
||
return
|
||
}
|
||
}
|
||
}
|
||
if x >= 10 {
|
||
if y > x {
|
||
if y > 10 { // ERROR "Proved Greater64"
|
||
return
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
func trans2(a, b []int, i int) {
|
||
if len(a) != len(b) {
|
||
return
|
||
}
|
||
|
||
_ = a[i]
|
||
_ = b[i] // ERROR "Proved IsInBounds$"
|
||
}
|
||
|
||
func trans3(a, b []int, i int) {
|
||
if len(a) > len(b) {
|
||
return
|
||
}
|
||
|
||
_ = a[i]
|
||
_ = b[i] // ERROR "Proved IsInBounds$"
|
||
}
|
||
|
||
// Derived from nat.cmp
|
||
func natcmp(x, y []uint) (r int) {
|
||
m := len(x)
|
||
n := len(y)
|
||
if m != n || m == 0 {
|
||
return
|
||
}
|
||
|
||
i := m - 1
|
||
for i > 0 && // ERROR "Induction variable: limits \(0,\?\], increment -1"
|
||
x[i] == // ERROR "Proved IsInBounds$"
|
||
y[i] { // ERROR "Proved IsInBounds$"
|
||
i--
|
||
}
|
||
|
||
switch {
|
||
case x[i] < // todo, cannot prove this because it's dominated by i<=0 || x[i]==y[i]
|
||
y[i]: // ERROR "Proved IsInBounds$"
|
||
r = -1
|
||
case x[i] > // ERROR "Proved IsInBounds$"
|
||
y[i]: // ERROR "Proved IsInBounds$"
|
||
r = 1
|
||
}
|
||
return
|
||
}
|
||
|
||
func suffix(s, suffix string) bool {
|
||
// todo, we're still not able to drop the bound check here in the general case
|
||
return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
|
||
}
|
||
|
||
func constsuffix(s string) bool {
|
||
return suffix(s, "abc") // ERROR "Proved IsSliceInBounds$"
|
||
}
|
||
|
||
//go:noinline
|
||
func useInt(a int) {
|
||
}
|
||
|
||
//go:noinline
|
||
func useSlice(a []int) {
|
||
}
|
||
|
||
func main() {
|
||
}
|