From 1f83a8c16cf1e9141e081759fb0f6c6f2acb5fdc Mon Sep 17 00:00:00 2001 From: Keith Randall Date: Tue, 31 Aug 2021 14:09:41 -0700 Subject: [PATCH] cmd/compile: use the zero value for results of impossible indexing 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 Run-TryBot: Keith Randall Reviewed-by: David Chase TryBot-Result: Go Bot --- src/cmd/compile/internal/ssagen/ssa.go | 3 ++- test/fixedbugs/issue48092.go | 17 +++++++++++++++++ 2 files changed, 19 insertions(+), 1 deletion(-) create mode 100644 test/fixedbugs/issue48092.go diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go index 77a350720fc..a64901305fe 100644 --- a/src/cmd/compile/internal/ssagen/ssa.go +++ b/src/cmd/compile/internal/ssagen/ssa.go @@ -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 diff --git a/test/fixedbugs/issue48092.go b/test/fixedbugs/issue48092.go new file mode 100644 index 00000000000..47b812c8d5d --- /dev/null +++ b/test/fixedbugs/issue48092.go @@ -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] +}