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go/test/prove.go
zdjones 69ff0ba798 cmd/compile: handle sign/zero extensions in prove, via update method 
Array accesses with index types smaller than the machine word size may
involve a sign or zero extension of the index value before bounds
checking. Currently, this defeats prove because the facts about the
original index value don't flow through the sign/zero extension.

This CL fixes this by looking back through value-preserving sign/zero
extensions when adding facts via Update and, where appropriate, applying
the same facts using the pre-extension value. This fix is enhanced by
also looking back through value-preserving extensions within
ft.isNonNegative to infer whether the extended value is known to be
non-negative. Without this additional isNonNegative enhancement, this
logic is rendered significantly less effective by the limitation
discussed in the next paragraph.

In Update, the application of facts to pre-extension values is limited
to cases where the domain of the new fact is consistent with the type of
the pre-extension value. There may be cases where this cross-domain
passing of facts is valid, but distinguishing them from the invalid
cases is difficult for me to reason about and to implement.
Assessing which cases to allow requires details about the context and
inferences behind the fact being applied which are not available
within Update. Additional difficulty arises from the fact that the SSA
does not curently differentiate extensions added by the compiler for
indexing operations, extensions added by the compiler for implicit
conversions, or explicit extensions from the source.

Examples of some cases that would need to be filtered correctly for
cross-domain facts:

(1) A uint8 is zero-extended to int for indexing (a value-preserving
zeroExt). When, if ever, can signed domain facts learned about the int be
applied to the uint8?

(2) An int8 is sign-extended to int16 (value-preserving) for an equality
comparison. Equality comparison facts are currently always learned in both
the signed and unsigned domains. When, if ever, can the unsigned facts
learned about the int16, from the int16 != int16 comparison, be applied
to the original int8?

This is an alternative to CL 122695 and CL 174309. Compared to CL 122695,
this CL differs in that the facts added about the pre-extension value will
pass through the Update method, where additional inferences are processed
(e.g. fence-post implications, see #29964). CL 174309 is limited to bounds
checks, so is narrower in application, and makes the code harder to read.

Fixes #26292.
Fixes #29964.
Fixes #15074

Removes 238 bounds checks from std/cmd.

Change-Id: I1f87c32ee672bfb8be397b27eab7a4c2f304893f
Reviewed-on: https://go-review.googlesource.com/c/go/+/174704
Run-TryBot: Zach Jones <zachj1@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Giovanni Bajo <rasky@develer.com>
2019-08-27 16:46:34 +00:00

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// +build amd64
// errorcheck -0 -d=ssa/prove/debug=1
// 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.
package main
import "math"
func f0(a []int) int {
a[0] = 1
a[0] = 1 // ERROR "Proved IsInBounds$"
a[6] = 1
a[6] = 1 // ERROR "Proved IsInBounds$"
a[5] = 1 // ERROR "Proved IsInBounds$"
a[5] = 1 // ERROR "Proved IsInBounds$"
return 13
}
func f1(a []int) int {
if len(a) <= 5 {
return 18
}
a[0] = 1 // ERROR "Proved IsInBounds$"
a[0] = 1 // ERROR "Proved IsInBounds$"
a[6] = 1
a[6] = 1 // ERROR "Proved IsInBounds$"
a[5] = 1 // ERROR "Proved IsInBounds$"
a[5] = 1 // ERROR "Proved IsInBounds$"
return 26
}
func f1b(a []int, i int, j uint) int {
if i >= 0 && i < len(a) {
return a[i] // ERROR "Proved IsInBounds$"
}
if i >= 10 && i < len(a) {
return a[i] // ERROR "Proved IsInBounds$"
}
if i >= 10 && i < len(a) {
return a[i] // ERROR "Proved IsInBounds$"
}
if i >= 10 && i < len(a) {
return a[i-10] // ERROR "Proved IsInBounds$"
}
if j < uint(len(a)) {
return a[j] // ERROR "Proved IsInBounds$"
}
return 0
}
func f1c(a []int, i int64) int {
c := uint64(math.MaxInt64 + 10) // overflows int
d := int64(c)
if i >= d && i < int64(len(a)) {
// d overflows, should not be handled.
return a[i]
}
return 0
}
func f2(a []int) int {
for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
a[i+1] = i
a[i+1] = i // ERROR "Proved IsInBounds$"
}
return 34
}
func f3(a []uint) int {
for i := uint(0); i < uint(len(a)); i++ {
a[i] = i // ERROR "Proved IsInBounds$"
}
return 41
}
func f4a(a, b, c int) int {
if a < b {
if a == b { // ERROR "Disproved Eq64$"
return 47
}
if a > b { // ERROR "Disproved Greater64$"
return 50
}
if a < b { // ERROR "Proved Less64$"
return 53
}
// We can't get to this point and prove knows that, so
// there's no message for the next (obvious) branch.
if a != a {
return 56
}
return 61
}
return 63
}
func f4b(a, b, c int) int {
if a <= b {
if a >= b {
if a == b { // ERROR "Proved Eq64$"
return 70
}
return 75
}
return 77
}
return 79
}
func f4c(a, b, c int) int {
if a <= b {
if a >= b {
if a != b { // ERROR "Disproved Neq64$"
return 73
}
return 75
}
return 77
}
return 79
}
func f4d(a, b, c int) int {
if a < b {
if a < c {
if a < b { // ERROR "Proved Less64$"
if a < c { // ERROR "Proved Less64$"
return 87
}
return 89
}
return 91
}
return 93
}
return 95
}
func f4e(a, b, c int) int {
if a < b {
if b > a { // ERROR "Proved Greater64$"
return 101
}
return 103
}
return 105
}
func f4f(a, b, c int) int {
if a <= b {
if b > a {
if b == a { // ERROR "Disproved Eq64$"
return 112
}
return 114
}
if b >= a { // ERROR "Proved Geq64$"
if b == a { // ERROR "Proved Eq64$"
return 118
}
return 120
}
return 122
}
return 124
}
func f5(a, b uint) int {
if a == b {
if a <= b { // ERROR "Proved Leq64U$"
return 130
}
return 132
}
return 134
}
// These comparisons are compile time constants.
func f6a(a uint8) int {
if a < a { // ERROR "Disproved Less8U$"
return 140
}
return 151
}
func f6b(a uint8) int {
if a < a { // ERROR "Disproved Less8U$"
return 140
}
return 151
}
func f6x(a uint8) int {
if a > a { // ERROR "Disproved Greater8U$"
return 143
}
return 151
}
func f6d(a uint8) int {
if a <= a { // ERROR "Proved Leq8U$"
return 146
}
return 151
}
func f6e(a uint8) int {
if a >= a { // ERROR "Proved Geq8U$"
return 149
}
return 151
}
func f7(a []int, b int) int {
if b < len(a) {
a[b] = 3
if b < len(a) { // ERROR "Proved Less64$"
a[b] = 5 // ERROR "Proved IsInBounds$"
}
}
return 161
}
func f8(a, b uint) int {
if a == b {
return 166
}
if a > b {
return 169
}
if a < b { // ERROR "Proved Less64U$"
return 172
}
return 174
}
func f9(a, b bool) int {
if a {
return 1
}
if a || b { // ERROR "Disproved Arg$"
return 2
}
return 3
}
func f10(a string) int {
n := len(a)
// We optimize comparisons with small constant strings (see cmd/compile/internal/gc/walk.go),
// so this string literal must be long.
if a[:n>>1] == "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" {
return 0
}
return 1
}
func f11a(a []int, i int) {
useInt(a[i])
useInt(a[i]) // ERROR "Proved IsInBounds$"
}
func f11b(a []int, i int) {
useSlice(a[i:])
useSlice(a[i:]) // ERROR "Proved IsSliceInBounds$"
}
func f11c(a []int, i int) {
useSlice(a[:i])
useSlice(a[:i]) // ERROR "Proved IsSliceInBounds$"
}
func f11d(a []int, i int) {
useInt(a[2*i+7])
useInt(a[2*i+7]) // ERROR "Proved IsInBounds$"
}
func f12(a []int, b int) {
useSlice(a[:b])
}
func f13a(a, b, c int, x bool) int {
if a > 12 {
if x {
if a < 12 { // ERROR "Disproved Less64$"
return 1
}
}
if x {
if a <= 12 { // ERROR "Disproved Leq64$"
return 2
}
}
if x {
if a == 12 { // ERROR "Disproved Eq64$"
return 3
}
}
if x {
if a >= 12 { // ERROR "Proved Geq64$"
return 4
}
}
if x {
if a > 12 { // ERROR "Proved Greater64$"
return 5
}
}
return 6
}
return 0
}
func f13b(a int, x bool) int {
if a == -9 {
if x {
if a < -9 { // ERROR "Disproved Less64$"
return 7
}
}
if x {
if a <= -9 { // ERROR "Proved Leq64$"
return 8
}
}
if x {
if a == -9 { // ERROR "Proved Eq64$"
return 9
}
}
if x {
if a >= -9 { // ERROR "Proved Geq64$"
return 10
}
}
if x {
if a > -9 { // ERROR "Disproved Greater64$"
return 11
}
}
return 12
}
return 0
}
func f13c(a int, x bool) int {
if a < 90 {
if x {
if a < 90 { // ERROR "Proved Less64$"
return 13
}
}
if x {
if a <= 90 { // ERROR "Proved Leq64$"
return 14
}
}
if x {
if a == 90 { // ERROR "Disproved Eq64$"
return 15
}
}
if x {
if a >= 90 { // ERROR "Disproved Geq64$"
return 16
}
}
if x {
if a > 90 { // ERROR "Disproved Greater64$"
return 17
}
}
return 18
}
return 0
}
func f13d(a int) int {
if a < 5 {
if a < 9 { // ERROR "Proved Less64$"
return 1
}
}
return 0
}
func f13e(a int) int {
if a > 9 {
if a > 5 { // ERROR "Proved Greater64$"
return 1
}
}
return 0
}
func f13f(a int64) int64 {
if a > math.MaxInt64 {
if a == 0 { // ERROR "Disproved Eq64$"
return 1
}
}
return 0
}
func f13g(a int) int {
if a < 3 {
return 5
}
if a > 3 {
return 6
}
if a == 3 { // ERROR "Proved Eq64$"
return 7
}
return 8
}
func f13h(a int) int {
if a < 3 {
if a > 1 {
if a == 2 { // ERROR "Proved Eq64$"
return 5
}
}
}
return 0
}
func f13i(a uint) int {
if a == 0 {
return 1
}
if a > 0 { // ERROR "Proved Greater64U$"
return 2
}
return 3
}
func f14(p, q *int, a []int) {
// This crazy ordering usually gives i1 the lowest value ID,
// j the middle value ID, and i2 the highest value ID.
// That used to confuse CSE because it ordered the args
// of the two + ops below differently.
// That in turn foiled bounds check elimination.
i1 := *p
j := *q
i2 := *p
useInt(a[i1+j])
useInt(a[i2+j]) // ERROR "Proved IsInBounds$"
}
func f15(s []int, x int) {
useSlice(s[x:])
useSlice(s[:x]) // ERROR "Proved IsSliceInBounds$"
}
func f16(s []int) []int {
if len(s) >= 10 {
return s[:10] // ERROR "Proved IsSliceInBounds$"
}
return nil
}
func f17(b []int) {
for i := 0; i < len(b); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
// This tests for i <= cap, which we can only prove
// using the derived relation between len and cap.
// This depends on finding the contradiction, since we
// don't query this condition directly.
useSlice(b[:i]) // ERROR "Proved IsSliceInBounds$"
}
}
func f18(b []int, x int, y uint) {
_ = b[x]
_ = b[y]
if x > len(b) { // ERROR "Disproved Greater64$"
return
}
if y > uint(len(b)) { // ERROR "Disproved Greater64U$"
return
}
if int(y) > len(b) { // ERROR "Disproved Greater64$"
return
}
}
func f19() (e int64, err error) {
// Issue 29502: slice[:0] is incorrectly disproved.
var stack []int64
stack = append(stack, 123)
if len(stack) > 1 {
panic("too many elements")
}
last := len(stack) - 1
e = stack[last]
// Buggy compiler prints "Disproved Geq64" for the next line.
stack = stack[:last] // ERROR "Proved IsSliceInBounds"
return e, nil
}
func sm1(b []int, x int) {
// Test constant argument to slicemask.
useSlice(b[2:8]) // ERROR "Proved slicemask not needed$"
// Test non-constant argument with known limits.
if cap(b) > 10 {
useSlice(b[2:]) // ERROR "Proved slicemask not needed$"
}
}
func lim1(x, y, z int) {
// Test relations between signed and unsigned limits.
if x > 5 {
if uint(x) > 5 { // ERROR "Proved Greater64U$"
return
}
}
if y >= 0 && y < 4 {
if uint(y) > 4 { // ERROR "Disproved Greater64U$"
return
}
if uint(y) < 5 { // ERROR "Proved Less64U$"
return
}
}
if z < 4 {
if uint(z) > 4 { // Not provable without disjunctions.
return
}
}
}
// fence1–4 correspond to the four fence-post implications.
func fence1(b []int, x, y int) {
// Test proofs that rely on fence-post implications.
if x+1 > y {
if x < y { // ERROR "Disproved Less64$"
return
}
}
if len(b) < cap(b) {
// This eliminates the growslice path.
b = append(b, 1) // ERROR "Disproved Greater64U$"
}
}
func fence2(x, y int) {
if x-1 < y {
if x > y { // ERROR "Disproved Greater64$"
return
}
}
}
func fence3(b, c []int, x, y int64) {
if x-1 >= y {
if x <= y { // Can't prove because x may have wrapped.
return
}
}
if x != math.MinInt64 && x-1 >= y {
if x <= y { // ERROR "Disproved Leq64$"
return
}
}
c[len(c)-1] = 0 // Can't prove because len(c) might be 0
if n := len(b); n > 0 {
b[n-1] = 0 // ERROR "Proved IsInBounds$"
}
}
func fence4(x, y int64) {
if x >= y+1 {
if x <= y {
return
}
}
if y != math.MaxInt64 && x >= y+1 {
if x <= y { // ERROR "Disproved Leq64$"
return
}
}
}
// 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$"
}
// oforuntil tests the pattern created by OFORUNTIL blocks. These are
// handled by addLocalInductiveFacts rather than findIndVar.
func oforuntil(b []int) {
i := 0
if len(b) > i {
top:
println(b[i]) // ERROR "Induction variable: limits \[0,\?\), increment 1$" "Proved IsInBounds$"
i++
if i < len(b) {
goto top
}
}
}
// The range tests below test the index variable of range loops.
// range1 compiles to the "efficiently indexable" form of a range loop.
func range1(b []int) {
for i, v := range b { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
b[i] = v + 1 // ERROR "Proved IsInBounds$"
if i < len(b) { // ERROR "Proved Less64$"
println("x")
}
if i >= 0 { // ERROR "Proved Geq64$"
println("x")
}
}
}
// range2 elements are larger, so they use the general form of a range loop.
func range2(b [][32]int) {
for i, v := range b {
b[i][0] = v[0] + 1 // ERROR "Induction variable: limits \[0,\?\), increment 1$" "Proved IsInBounds$"
if i < len(b) { // ERROR "Proved Less64$"
println("x")
}
if i >= 0 { // ERROR "Proved Geq64$"
println("x")
}
}
}
// signhint1-2 test whether the hint (int >= 0) is propagated into the loop.
func signHint1(i int, data []byte) {
if i >= 0 {
for i < len(data) { // ERROR "Induction variable: limits \[\?,\?\), increment 1$"
_ = data[i] // ERROR "Proved IsInBounds$"
i++
}
}
}
func signHint2(b []byte, n int) {
if n < 0 {
panic("")
}
_ = b[25]
for i := n; i <= 25; i++ { // ERROR "Induction variable: limits \[\?,25\], increment 1$"
b[i] = 123 // ERROR "Proved IsInBounds$"
}
}
// indexGT0 tests whether prove learns int index >= 0 from bounds check.
func indexGT0(b []byte, n int) {
_ = b[n]
_ = b[25]
for i := n; i <= 25; i++ { // ERROR "Induction variable: limits \[\?,25\], increment 1$"
b[i] = 123 // ERROR "Proved IsInBounds$"
}
}
// Induction variable in unrolled loop.
func unrollUpExcl(a []int) int {
var i, x int
for i = 0; i < len(a)-1; i += 2 { // ERROR "Induction variable: limits \[0,\?\), increment 2$"
x += a[i] // ERROR "Proved IsInBounds$"
x += a[i+1]
}
if i == len(a)-1 {
x += a[i]
}
return x
}
// Induction variable in unrolled loop.
func unrollUpIncl(a []int) int {
var i, x int
for i = 0; i <= len(a)-2; i += 2 { // ERROR "Induction variable: limits \[0,\?\], increment 2$"
x += a[i]
x += a[i+1]
}
if i == len(a)-1 {
x += a[i]
}
return x
}
// Induction variable in unrolled loop.
func unrollDownExcl0(a []int) int {
var i, x int
for i = len(a) - 1; i > 0; i -= 2 { // ERROR "Induction variable: limits \(0,\?\], increment 2$"
x += a[i] // ERROR "Proved IsInBounds$"
x += a[i-1] // ERROR "Proved IsInBounds$"
}
if i == 0 {
x += a[i]
}
return x
}
// Induction variable in unrolled loop.
func unrollDownExcl1(a []int) int {
var i, x int
for i = len(a) - 1; i >= 1; i -= 2 { // ERROR "Induction variable: limits \[1,\?\], increment 2$"
x += a[i] // ERROR "Proved IsInBounds$"
x += a[i-1] // ERROR "Proved IsInBounds$"
}
if i == 0 {
x += a[i]
}
return x
}
// Induction variable in unrolled loop.
func unrollDownInclStep(a []int) int {
var i, x int
for i = len(a); i >= 2; i -= 2 { // ERROR "Induction variable: limits \[2,\?\], increment 2$"
x += a[i-1] // ERROR "Proved IsInBounds$"
x += a[i-2]
}
if i == 1 {
x += a[i-1]
}
return x
}
// Not an induction variable (step too large)
func unrollExclStepTooLarge(a []int) int {
var i, x int
for i = 0; i < len(a)-1; i += 3 {
x += a[i]
x += a[i+1]
}
if i == len(a)-1 {
x += a[i]
}
return x
}
// Not an induction variable (step too large)
func unrollInclStepTooLarge(a []int) int {
var i, x int
for i = 0; i <= len(a)-2; i += 3 {
x += a[i]
x += a[i+1]
}
if i == len(a)-1 {
x += a[i]
}
return x
}
// Not an induction variable (min too small, iterating down)
func unrollDecMin(a []int) int {
var i, x int
for i = len(a); i >= math.MinInt64; i -= 2 {
x += a[i-1]
x += a[i-2]
}
if i == 1 { // ERROR "Disproved Eq64$"
x += a[i-1]
}
return x
}
// Not an induction variable (min too small, iterating up -- perhaps could allow, but why bother?)
func unrollIncMin(a []int) int {
var i, x int
for i = len(a); i >= math.MinInt64; i += 2 {
x += a[i-1]
x += a[i-2]
}
if i == 1 { // ERROR "Disproved Eq64$"
x += a[i-1]
}
return x
}
// The 4 xxxxExtNto64 functions below test whether prove is looking
// through value-preserving sign/zero extensions of index values (issue #26292).
// Look through all extensions
func signExtNto64(x []int, j8 int8, j16 int16, j32 int32) int {
if len(x) < 22 {
return 0
}
if j8 >= 0 && j8 < 22 {
return x[j8] // ERROR "Proved IsInBounds$"
}
if j16 >= 0 && j16 < 22 {
return x[j16] // ERROR "Proved IsInBounds$"
}
if j32 >= 0 && j32 < 22 {
return x[j32] // ERROR "Proved IsInBounds$"
}
return 0
}
func zeroExtNto64(x []int, j8 uint8, j16 uint16, j32 uint32) int {
if len(x) < 22 {
return 0
}
if j8 >= 0 && j8 < 22 {
return x[j8] // ERROR "Proved IsInBounds$"
}
if j16 >= 0 && j16 < 22 {
return x[j16] // ERROR "Proved IsInBounds$"
}
if j32 >= 0 && j32 < 22 {
return x[j32] // ERROR "Proved IsInBounds$"
}
return 0
}
// Process fence-post implications through 32to64 extensions (issue #29964)
func signExt32to64Fence(x []int, j int32) int {
if x[j] != 0 {
return 1
}
if j > 0 && x[j-1] != 0 { // ERROR "Proved IsInBounds$"
return 1
}
return 0
}
func zeroExt32to64Fence(x []int, j uint32) int {
if x[j] != 0 {
return 1
}
if j > 0 && x[j-1] != 0 { // ERROR "Proved IsInBounds$"
return 1
}
return 0
}
//go:noinline
func useInt(a int) {
}
//go:noinline
func useSlice(a []int) {
}
func main() {
}
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