[release-branch.go1.11] cmd/compile: check for negative upper bound to IsSliceInBounds

IsSliceInBounds(x, y) asserts that y is not negative, but
there were cases where this is not true.  Change code
generation to ensure that this is true when it's not obviously
true.  Prove phase cleans a few of these out.

With this change the compiler text section is 0.06% larger,
that is, not very much.  Benchmarking still TBD, may need
to wait for access to a benchmarking box (next week).

Also corrected run.go to handle '?' in -update_errors output.

Fixes #28799.

Change-Id: Ia8af90bc50a91ae6e934ef973def8d3f398fac7b
Reviewed-on: https://go-review.googlesource.com/c/152477
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
(cherry picked from commit ea6259d5e9d57f247b7d877d4d04602b74ae5155)
Reviewed-on: https://go-review.googlesource.com/c/153638

5 files changed, 131 insertions, 57 deletions

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index af43da6275..5b84a0a5bb 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -3863,6 +3863,18 @@ func (s *state) boundsCheck(idx, len *ssa.Value) {
 	s.check(cmp, panicindex)
 }
 
+func couldBeNegative(v *ssa.Value) bool {
+	switch v.Op {
+	case ssa.OpSliceLen, ssa.OpSliceCap, ssa.OpStringLen:
+		return false
+	case ssa.OpConst64:
+		return v.AuxInt < 0
+	case ssa.OpConst32:
+		return int32(v.AuxInt) < 0
+	}
+	return true
+}
+
 // sliceBoundsCheck generates slice bounds checking code. Checks if 0 <= idx <= len, branches to exit if not.
 // Starts a new block on return.
 // idx and len are already converted to full int width.
@@ -3870,6 +3882,15 @@ func (s *state) sliceBoundsCheck(idx, len *ssa.Value) {
 	if Debug['B'] != 0 {
 		return
 	}
+	if couldBeNegative(len) {
+		// OpIsSliceInBounds requires second arg not negative; if it's not obviously true, must check.
+		cmpop := ssa.OpGeq64
+		if len.Type.Size() == 4 {
+			cmpop = ssa.OpGeq32
+		}
+		cmp := s.newValue2(cmpop, types.Types[TBOOL], len, s.zeroVal(len.Type))
+		s.check(cmp, panicslice)
+	}
 
 	// bounds check
 	cmp := s.newValue2(ssa.OpIsSliceInBounds, types.Types[TBOOL], idx, len)
diff --git a/test/fixedbugs/issue28797.go b/test/fixedbugs/issue28797.go
new file mode 100644
index 0000000000..480c1059b8
--- /dev/null
+++ b/test/fixedbugs/issue28797.go
@@ -0,0 +1,53 @@
+// run
+
+// Copyright 2018 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 (
+	"fmt"
+)
+
+// test expects f to panic, but not to run out of memory,
+// which is a non-panic fatal error.  OOM results from failure
+// to properly check negative limit.
+func test(f func()) {
+	defer func() {
+		r := recover()
+		if r == nil {
+			panic("panic wasn't recoverable")
+		}
+	}()
+	f()
+}
+
+//go:noinline
+func id(x int) int {
+	return x
+}
+
+func main() {
+	test(foo)
+	test(bar)
+}
+
+func foo() {
+	b := make([]byte, 0)
+	b = append(b, 1)
+	id(len(b))
+	id(len(b) - 2)
+	s := string(b[1 : len(b)-2])
+	fmt.Println(s)
+}
+
+func bar() {
+	b := make([]byte, 1)
+	b = append(b, 1)
+	i := id(-1)
+	if i < len(b) { // establish value is not too large.
+		s := string(b[1:i]) // should check for negative also.
+		fmt.Println(s)
+	}
+}
diff --git a/test/loopbce.go b/test/loopbce.go
index b4bf797497..81f2524e95 100644
--- a/test/loopbce.go
+++ b/test/loopbce.go
@@ -6,7 +6,7 @@ package main
 func f0a(a []int) int {
 	x := 0
 	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		x += a[i] // ERROR "Proved IsInBounds$"
+		x += a[i] // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -14,7 +14,7 @@ func f0a(a []int) int {
 func f0b(a []int) int {
 	x := 0
 	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		b := a[i:] // ERROR "Proved IsSliceInBounds$"
+		b := a[i:] // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		x += b[0]
 	}
 	return x
@@ -23,7 +23,7 @@ func f0b(a []int) int {
 func f0c(a []int) int {
 	x := 0
 	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		b := a[:i+1] // ERROR "Proved IsSliceInBounds$"
+		b := a[:i+1] // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		x += b[0]
 	}
 	return x
@@ -40,7 +40,7 @@ func f1(a []int) int {
 func f2(a []int) int {
 	x := 0
 	for i := 1; i < len(a); i++ { // ERROR "Induction variable: limits \[1,\?\), increment 1$"
-		x += a[i] // ERROR "Proved IsInBounds$"
+		x += a[i] // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -48,7 +48,7 @@ func f2(a []int) int {
 func f4(a [10]int) int {
 	x := 0
 	for i := 0; i < len(a); i += 2 { // ERROR "Induction variable: limits \[0,10\), increment 2$"
-		x += a[i] // ERROR "Proved IsInBounds$"
+		x += a[i] // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -63,7 +63,7 @@ func f5(a [10]int) int {
 
 func f6(a []int) {
 	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		b := a[0:i] // ERROR "Proved IsSliceInBounds$"
+		b := a[0:i] // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$" "(\([0-9]+\) )?Proved Geq64$"
 		f6(b)
 	}
 }
@@ -71,7 +71,7 @@ func f6(a []int) {
 func g0a(a string) int {
 	x := 0
 	for i := 0; i < len(a); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		x += int(a[i]) // ERROR "Proved IsInBounds$"
+		x += int(a[i]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -79,7 +79,7 @@ func g0a(a string) int {
 func g0b(a string) int {
 	x := 0
 	for i := 0; len(a) > i; i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		x += int(a[i]) // ERROR "Proved IsInBounds$"
+		x += int(a[i]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -87,7 +87,7 @@ func g0b(a string) int {
 func g0c(a string) int {
 	x := 0
 	for i := len(a); i > 0; i-- { // ERROR "Induction variable: limits \(0,\?\], increment 1$"
-		x += int(a[i-1]) // ERROR "Proved IsInBounds$"
+		x += int(a[i-1]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -95,7 +95,7 @@ func g0c(a string) int {
 func g0d(a string) int {
 	x := 0
 	for i := len(a); 0 < i; i-- { // ERROR "Induction variable: limits \(0,\?\], increment 1$"
-		x += int(a[i-1]) // ERROR "Proved IsInBounds$"
+		x += int(a[i-1]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -103,7 +103,7 @@ func g0d(a string) int {
 func g0e(a string) int {
 	x := 0
 	for i := len(a) - 1; i >= 0; i-- { // ERROR "Induction variable: limits \[0,\?\], increment 1$"
-		x += int(a[i]) // ERROR "Proved IsInBounds$"
+		x += int(a[i]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -111,7 +111,7 @@ func g0e(a string) int {
 func g0f(a string) int {
 	x := 0
 	for i := len(a) - 1; 0 <= i; i-- { // ERROR "Induction variable: limits \[0,\?\], increment 1$"
-		x += int(a[i]) // ERROR "Proved IsInBounds$"
+		x += int(a[i]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -120,7 +120,7 @@ func g1() int {
 	a := "evenlength"
 	x := 0
 	for i := 0; i < len(a); i += 2 { // ERROR "Induction variable: limits \[0,10\), increment 2$"
-		x += int(a[i]) // ERROR "Proved IsInBounds$"
+		x += int(a[i]) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return x
 }
@@ -130,7 +130,7 @@ func g2() int {
 	x := 0
 	for i := 0; i < len(a); i += 2 { // ERROR "Induction variable: limits \[0,10\), increment 2$"
 		j := i
-		if a[i] == 'e' { // ERROR "Proved IsInBounds$"
+		if a[i] == 'e' { // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 			j = j + 1
 		}
 		x += int(a[j])
@@ -141,27 +141,27 @@ func g2() int {
 func g3a() {
 	a := "this string has length 25"
 	for i := 0; i < len(a); i += 5 { // ERROR "Induction variable: limits \[0,25\), increment 5$"
-		useString(a[i:]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[i:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		useString(a[:i+3])
 	}
 }
 
 func g3b(a string) {
 	for i := 0; i < len(a); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		useString(a[i+1:]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[i+1:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 	}
 }
 
 func g3c(a string) {
 	for i := 0; i < len(a); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		useString(a[:i+1]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[:i+1]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 	}
 }
 
 func h1(a []byte) {
 	c := a[:128]
 	for i := range c { // ERROR "Induction variable: limits \[0,128\), increment 1$"
-		c[i] = byte(i) // ERROR "Proved IsInBounds$"
+		c[i] = byte(i) // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 }
 
@@ -174,11 +174,11 @@ func h2(a []byte) {
 func k0(a [100]int) [100]int {
 	for i := 10; i < 90; i++ { // ERROR "Induction variable: limits \[10,90\), increment 1$"
 		a[i-11] = i
-		a[i-10] = i // ERROR "Proved IsInBounds$"
-		a[i-5] = i  // ERROR "Proved IsInBounds$"
-		a[i] = i    // ERROR "Proved IsInBounds$"
-		a[i+5] = i  // ERROR "Proved IsInBounds$"
-		a[i+10] = i // ERROR "Proved IsInBounds$"
+		a[i-10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
+		a[i-5] = i  // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
+		a[i] = i    // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
+		a[i+5] = i  // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
+		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
 	}
 	return a
@@ -186,13 +186,13 @@ func k0(a [100]int) [100]int {
 
 func k1(a [100]int) [100]int {
 	for i := 10; i < 90; i++ { // ERROR "Induction variable: limits \[10,90\), increment 1$"
-		useSlice(a[:i-11])
-		useSlice(a[:i-10]) // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[:i-5])  // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[:i])    // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[:i+5])  // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[:i+10]) // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[:i+11]) // ERROR "Proved IsSliceInBounds$"
+		useSlice(a[:i-11]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[:i-10]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[:i-5])  // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[:i])    // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$" "(\([0-9]+\) )?Proved Geq64$"
+		useSlice(a[:i+5])  // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[:i+10]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[:i+11]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		useSlice(a[:i+12])
 
 	}
@@ -202,12 +202,12 @@ func k1(a [100]int) [100]int {
 func k2(a [100]int) [100]int {
 	for i := 10; i < 90; i++ { // ERROR "Induction variable: limits \[10,90\), increment 1$"
 		useSlice(a[i-11:])
-		useSlice(a[i-10:]) // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[i-5:])  // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[i:])    // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[i+5:])  // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[i+10:]) // ERROR "Proved IsSliceInBounds$"
-		useSlice(a[i+11:]) // ERROR "Proved IsSliceInBounds$"
+		useSlice(a[i-10:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[i-5:])  // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[i:])    // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[i+5:])  // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[i+10:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
+		useSlice(a[i+11:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		useSlice(a[i+12:])
 	}
 	return a
@@ -216,7 +216,7 @@ func k2(a [100]int) [100]int {
 func k3(a [100]int) [100]int {
 	for i := -10; i < 90; i++ { // ERROR "Induction variable: limits \[-10,90\), increment 1$"
 		a[i+9] = i
-		a[i+10] = i // ERROR "Proved IsInBounds$"
+		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
 	}
 	return a
@@ -225,7 +225,7 @@ func k3(a [100]int) [100]int {
 func k3neg(a [100]int) [100]int {
 	for i := 89; i > -11; i-- { // ERROR "Induction variable: limits \(-11,89\], increment 1$"
 		a[i+9] = i
-		a[i+10] = i // ERROR "Proved IsInBounds$"
+		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
 	}
 	return a
@@ -234,7 +234,7 @@ func k3neg(a [100]int) [100]int {
 func k3neg2(a [100]int) [100]int {
 	for i := 89; i >= -10; i-- { // ERROR "Induction variable: limits \[-10,89\], increment 1$"
 		a[i+9] = i
-		a[i+10] = i // ERROR "Proved IsInBounds$"
+		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
 	}
 	return a
@@ -243,16 +243,16 @@ func k3neg2(a [100]int) [100]int {
 func k4(a [100]int) [100]int {
 	min := (-1) << 63
 	for i := min; i < min+50; i++ { // ERROR "Induction variable: limits \[-9223372036854775808,-9223372036854775758\), increment 1$"
-		a[i-min] = i // ERROR "Proved IsInBounds$"
+		a[i-min] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return a
 }
 
 func k5(a [100]int) [100]int {
 	max := (1 << 63) - 1
-	for i := max - 50; i < max; i++ { // ERROR "Induction variable: limits \[9223372036854775757,9223372036854775807\), increment 1"
-		a[i-max+50] = i   // ERROR "Proved IsInBounds$"
-		a[i-(max-70)] = i // ERROR "Proved IsInBounds$"
+	for i := max - 50; i < max; i++ { // ERROR "Induction variable: limits \[9223372036854775757,9223372036854775807\), increment 1$"
+		a[i-max+50] = i   // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
+		a[i-(max-70)] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 	}
 	return a
 }
@@ -275,17 +275,17 @@ func nobce1() {
 
 func nobce2(a string) {
 	for i := int64(0); i < int64(len(a)); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		useString(a[i:]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[i:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 	}
 	for i := int64(0); i < int64(len(a))-31337; i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		useString(a[i:]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[i:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 	}
 	for i := int64(0); i < int64(len(a))+int64(-1<<63); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		useString(a[i:]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[i:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 	}
 	j := int64(len(a)) - 123
 	for i := int64(0); i < j+123+int64(-1<<63); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
-		useString(a[i:]) // ERROR "Proved IsSliceInBounds$"
+		useString(a[i:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 	}
 	for i := int64(0); i < j+122+int64(-1<<63); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
 		// len(a)-123+122+MinInt overflows when len(a) == 0, so a bound check is needed here
diff --git a/test/prove.go b/test/prove.go
index 79256893b3..0de6bd63b4 100644
--- a/test/prove.go
+++ b/test/prove.go
@@ -62,7 +62,7 @@ func f1c(a []int, i int64) int {
 }
 
 func f2(a []int) int {
-	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1"
+	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
 		a[i+1] = i
 		a[i+1] = i // ERROR "Proved IsInBounds$"
 	}
@@ -269,7 +269,7 @@ func f11b(a []int, i int) {
 
 func f11c(a []int, i int) {
 	useSlice(a[:i])
-	useSlice(a[:i]) // ERROR "Proved IsSliceInBounds$"
+	useSlice(a[:i]) // ERROR "Proved Geq64$" "Proved IsSliceInBounds$"
 }
 
 func f11d(a []int, i int) {
@@ -464,12 +464,12 @@ func f16(s []int) []int {
 }
 
 func f17(b []int) {
-	for i := 0; i < len(b); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1"
+	for i := 0; i < len(b); i++ { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
 		// This tests for i <= cap, which we can only prove
 		// using the derived relation between len and cap.
 		// This depends on finding the contradiction, since we
 		// don't query this condition directly.
-		useSlice(b[:i]) // ERROR "Proved IsSliceInBounds$"
+		useSlice(b[:i]) // ERROR "Proved Geq64$" "Proved IsSliceInBounds$"
 	}
 }
 
@@ -579,18 +579,18 @@ func fence4(x, y int64) {
 func trans1(x, y int64) {
 	if x > 5 {
 		if y > x {
-			if y > 2 { // ERROR "Proved Greater64"
+			if y > 2 { // ERROR "Proved Greater64$"
 				return
 			}
 		} else if y == x {
-			if y > 5 { // ERROR "Proved Greater64"
+			if y > 5 { // ERROR "Proved Greater64$"
 				return
 			}
 		}
 	}
 	if x >= 10 {
 		if y > x {
-			if y > 10 { // ERROR "Proved Greater64"
+			if y > 10 { // ERROR "Proved Greater64$"
 				return
 			}
 		}
@@ -624,7 +624,7 @@ func natcmp(x, y []uint) (r int) {
 	}
 
 	i := m - 1
-	for i > 0 && // ERROR "Induction variable: limits \(0,\?\], increment 1"
+	for i > 0 && // ERROR "Induction variable: limits \(0,\?\], increment 1$"
 		x[i] == // ERROR "Proved IsInBounds$"
 			y[i] { // ERROR "Proved IsInBounds$"
 		i--
@@ -686,7 +686,7 @@ func range2(b [][32]int) {
 		if i < len(b) {    // ERROR "Proved Less64$"
 			println("x")
 		}
-		if i >= 0 { // ERROR "Proved Geq64"
+		if i >= 0 { // ERROR "Proved Geq64$"
 			println("x")
 		}
 	}
diff --git a/test/run.go b/test/run.go
index 99ef79feb1..5a81da8d67 100644
--- a/test/run.go
+++ b/test/run.go
@@ -1180,7 +1180,7 @@ func (t *test) updateErrors(out, file string) {
 		msg := errStr[colon2+2:]
 		msg = strings.Replace(msg, file, base, -1) // normalize file mentions in error itself
 		msg = strings.TrimLeft(msg, " \t")
-		for _, r := range []string{`\`, `*`, `+`, `[`, `]`, `(`, `)`} {
+		for _, r := range []string{`\`, `*`, `+`, `?`, `[`, `]`, `(`, `)`} {
 			msg = strings.Replace(msg, r, `\`+r, -1)
 		}
 		msg = strings.Replace(msg, `"`, `.`, -1)