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var a []int = ... p := &a[0] _ = *p We don't need to nil check on the 3rd line. If the bounds check on the 2nd line passes, we know p is non-nil. We rely on the fact that any cap>0 slice has a non-nil pointer as its pointer to the backing array. This is true for all safely-constructed slices, and I don't see any reason why someone would violate this rule using unsafe. R=go1.13 Fixes #30366 Change-Id: I3ed764fcb72cfe1fbf963d8c1a82e24e3b6dead7 Reviewed-on: https://go-review.googlesource.com/c/163740 Run-TryBot: Keith Randall <khr@golang.org> Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
74 lines
1.6 KiB
Go
74 lines
1.6 KiB
Go
// asmcheck
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// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package codegen
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// This file contains code generation tests related to the handling of
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// slice types.
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// ------------------ //
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// Clear //
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// ------------------ //
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// Issue #5373 optimize memset idiom
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func SliceClear(s []int) []int {
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// amd64:`.*memclrNoHeapPointers`
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for i := range s {
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s[i] = 0
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}
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return s
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}
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func SliceClearPointers(s []*int) []*int {
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// amd64:`.*memclrHasPointers`
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for i := range s {
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s[i] = nil
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}
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return s
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}
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// ------------------ //
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// Extension //
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// ------------------ //
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// Issue #21266 - avoid makeslice in append(x, make([]T, y)...)
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func SliceExtensionConst(s []int) []int {
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// amd64:`.*runtime\.memclrNoHeapPointers`
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// amd64:-`.*runtime\.makeslice`
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// amd64:-`.*runtime\.panicmakeslicelen`
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return append(s, make([]int, 1<<2)...)
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}
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func SliceExtensionPointer(s []*int, l int) []*int {
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// amd64:`.*runtime\.memclrHasPointers`
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// amd64:-`.*runtime\.makeslice`
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return append(s, make([]*int, l)...)
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}
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func SliceExtensionVar(s []byte, l int) []byte {
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// amd64:`.*runtime\.memclrNoHeapPointers`
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// amd64:-`.*runtime\.makeslice`
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return append(s, make([]byte, l)...)
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}
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func SliceExtensionInt64(s []int, l64 int64) []int {
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// 386:`.*runtime\.makeslice`
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// 386:-`.*runtime\.memclr`
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return append(s, make([]int, l64)...)
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}
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// ---------------------- //
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// Nil check of &s[0] //
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// ---------------------- //
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// See issue 30366
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func SliceNilCheck(s []int) {
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p := &s[0]
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// amd64:-`TESTB`
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_ = *p
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}
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