From 3e54ca9a4624fda0bcd76192aa529e826ef12b4f Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 16 Mar 2016 18:22:58 -0400 Subject: [PATCH] cmd/compile: omit write barrier when assigning global function Currently we generate write barriers when the right side of an assignment is a global function. This doesn't fall into the existing case of storing an address of a global because we haven't lowered the function to a pointer yet. This write barrier is unnecessary, so eliminate it. Fixes #13901. Change-Id: Ibc10e00a8803db0fd75224b66ab94c3737842a79 Reviewed-on: https://go-review.googlesource.com/20772 Run-TryBot: Austin Clements Reviewed-by: Keith Randall --- src/cmd/compile/internal/gc/walk.go | 6 ++++++ test/writebarrier.go | 10 ++++++++++ 2 files changed, 16 insertions(+) diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go index b4c38ec12ba..69c8390fe0f 100644 --- a/src/cmd/compile/internal/gc/walk.go +++ b/src/cmd/compile/internal/gc/walk.go @@ -2140,6 +2140,12 @@ func needwritebarrier(l *Node, r *Node) bool { return false } + // No write barrier for storing global function, which is live + // no matter what. + if r.Op == ONAME && r.Class == PFUNC { + return false + } + // Otherwise, be conservative and use write barrier. return true } diff --git a/test/writebarrier.go b/test/writebarrier.go index dcd20a02252..e591eaab32b 100644 --- a/test/writebarrier.go +++ b/test/writebarrier.go @@ -158,3 +158,13 @@ func t1(i interface{}) **int { } return nil } + +type T17 struct { + f func(*T17) +} + +func f17(x *T17) { + // See golang.org/issue/13901 + x.f = f17 // no barrier + x.f = func(y *T17) { *y = *x } // ERROR "write barrier" +}