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cmd/compile: use the zero value for results of impossible indexing

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type A [0]int
var a A
x := a[i]

Use the zero value for x instead of the "impossible" value. That lets
us at least compile code like this with -B, even though it can't
possibly run correctly.

Fixes #48092

Change-Id: Idad5cfab49e05f375c069b05addceed68a15299f
Reviewed-on: https://go-review.googlesource.com/c/go/+/346589
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Keith Randall 2021-08-31 14:09:41 -07:00
parent bb0b511738
commit 1f83a8c16c
2 changed files with 19 additions and 1 deletions
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3
src/cmd/compile/internal/ssagen/ssa.go
View File

@ -3014,7 +3014,8 @@ func (s *state) expr(n ir.Node) *ssa.Value {
z := s.constInt(types.Types[types.TINT], 0)
s.boundsCheck(z, z, ssa.BoundsIndex, false)
// The return value won't be live, return junk.
return s.newValue0(ssa.OpUnknown, n.Type())
// But not quite junk, in case bounds checks are turned off. See issue 48092.
return s.zeroVal(n.Type())
}
len := s.constInt(types.Types[types.TINT], bound)
s.boundsCheck(i, len, ssa.BoundsIndex, n.Bounded()) // checks i == 0

17
test/fixedbugs/issue48092.go Normal file
View File

@ -0,0 +1,17 @@
// compile -B
// Copyright 2021 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.
// Make sure that we can at least compile this code
// successfully with -B. We can't ever produce the right
// answer at runtime with -B, as the access must panic.
package p
type A [0]byte
func (a *A) Get(i int) byte {
return a[i]
}