Commit 26c7b4fb authored by Anthony Canino's avatar Anthony Canino Committed by Russ Cox

cmd/compile: "abc"[1] is not an ideal constant

"abc"[1] is not like 'b', in that -"abc"[1] is uint8 math, not ideal constant math.
Delay the constantification until after ideal constant folding is over.

Fixes #11370.

Change-Id: Iba2fc00ca2455959e7bab8f4b8b4aac14b1f9858
Reviewed-on: https://go-review.googlesource.com/15740
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: default avatarRuss Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
parent 0da30d5c
......@@ -1941,6 +1941,12 @@ func (s *state) expr(n *Node) *ssa.Value {
case OINDEX:
switch {
case n.Left.Type.IsString():
if n.Bounded && Isconst(n.Left, CTSTR) && Isconst(n.Right, CTINT) {
// Replace "abc"[1] with 'b'.
// Delayed until now because "abc"[1] is not an ideal constant.
// See test/fixedbugs/issue11370.go.
return s.newValue0I(ssa.OpConst8, Types[TUINT8], int64(int8(n.Left.Val().U.(string)[n.Right.Int64()])))
}
a := s.expr(n.Left)
i := s.expr(n.Right)
i = s.extendIndex(i, panicindex)
......
......@@ -1263,18 +1263,8 @@ opswitch:
if Debug['m'] != 0 && n.Bounded && !Isconst(n.Right, CTINT) {
Warn("index bounds check elided")
}
if smallintconst(n.Right) {
if !n.Bounded {
yyerror("index out of bounds")
} else {
// replace "abc"[1] with 'b'.
// delayed until now because "abc"[1] is not
// an ideal constant.
v := n.Right.Int64()
Nodconst(n, n.Type, int64(n.Left.Val().U.(string)[v]))
n.Typecheck = 1
}
if smallintconst(n.Right) && !n.Bounded {
yyerror("index out of bounds")
}
}
......
// compile
// Copyright 2015 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.
// issue 11370: cmd/compile: "0"[0] should not be a constant
package p
func main() {
println(-"abc"[1] >> 1)
}
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