go/test/nowritebarrier.go

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// errorcheck -+
// Copyright 2016 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.
// Test go:nowritebarrier and related directives.
package p
type t struct {
f *t
}
var x t
var y *t
//go:nowritebarrier
func a1() {
x.f = y // ERROR "write barrier prohibited"
a2() // no error
}
//go:noinline
func a2() {
x.f = y
}
//go:nowritebarrierrec
func b1() {
b2()
}
//go:noinline
func b2() {
x.f = y // ERROR "write barrier prohibited by caller"
}
// Test recursive cycles through nowritebarrierrec and yeswritebarrierrec.
//go:nowritebarrierrec
func c1() {
c2()
}
//go:yeswritebarrierrec
func c2() {
c3()
}
func c3() {
x.f = y
c4()
}
//go:nowritebarrierrec
func c4() {
c2()
}
//go:nowritebarrierrec
func d1() {
d2()
}
func d2() {
d3()
}
cmd/compile: allow mid-stack inlining when there is a cycle of recursion We still disallow inlining for an immediately-recursive function, but allow inlining if a function is in a recursion chain. If all functions in the recursion chain are simple, then we could inline forever down the recursion chain (eventually running out of stack on the compiler), so we add a map to keep track of the functions we have already inlined at a call site. We stop inlining when we reach a function that we have already inlined in the recursive chain. Of course, normally the inlining will have stopped earlier, because of the cost function. We could also limit the depth of inlining by a simple count (say, limit max inlining of 10 at any given site). Would that limit other opportunities too much? Added a test in test/inline.go. runtime.BenchmarkStackCopyNoCache() is also already a good test that triggers the check to stop inlining when we reach the start of the recursive chain again. For the bent benchmark suite, the performance improvement was mostly not statistically significant, but the geomean averaged out to: -0.68%. The text size increase was less than .1% for all bent benchmarks. The cmd/go text size increase was 0.02% and the cmd/compile text size increase was .1%. Fixes #29737 Change-Id: I892fa84bb07a947b3125ec8f25ed0e508bf2bdf5 Reviewed-on: https://go-review.googlesource.com/c/go/+/226818 Run-TryBot: Dan Scales <danscales@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>
2020-04-01 03:24:05 +00:00
//go:noinline
func d3() {
x.f = y // ERROR "write barrier prohibited by caller"
d4()
}
//go:yeswritebarrierrec
func d4() {
d2()
}
cmd/compile: improve coverage of nowritebarrierrec check The current go:nowritebarrierrec checker has two problems that limit its coverage: 1. It doesn't understand that systemstack calls its argument, which means there are several cases where we fail to detect prohibited write barriers. 2. It only observes calls in the AST, so calls constructed during lowering by SSA aren't followed. This CL completely rewrites this checker to address these issues. The current checker runs entirely after walk and uses visitBottomUp, which introduces several problems for checking across systemstack. First, visitBottomUp itself doesn't understand systemstack calls, so the callee may be ordered after the caller, causing the checker to fail to propagate constraints. Second, many systemstack calls are passed a closure, which is quite difficult to resolve back to the function definition after transformclosure and walk have run. Third, visitBottomUp works exclusively on the AST, so it can't observe calls created by SSA. To address these problems, this commit splits the check into two phases and rewrites it to use a call graph generated during SSA lowering. The first phase runs before transformclosure/walk and simply records systemstack arguments when they're easy to get. Then, it modifies genssa to record static call edges at the point where we're lowering to Progs (which is the latest point at which position information is conveniently available). Finally, the second phase runs after all functions have been lowered and uses a direct BFS walk of the call graph (combining systemstack calls with static calls) to find prohibited write barriers and construct nice error messages. Fixes #22384. For #22460. Change-Id: I39668f7f2366ab3c1ab1a71eaf25484d25349540 Reviewed-on: https://go-review.googlesource.com/72773 Run-TryBot: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
2017-10-22 20:36:27 +00:00
//go:noinline
func systemstack(func()) {}
//go:nowritebarrierrec
func e1() {
systemstack(e2)
systemstack(func() {
x.f = y // ERROR "write barrier prohibited by caller"
})
}
func e2() {
x.f = y // ERROR "write barrier prohibited by caller"
}