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cmd/compile: special case nowritebarrierrec for allocm

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allocm is a very unusual function: it is specifically designed to
allocate in contexts where m.p is nil by temporarily taking over a P.
Since allocm is used in many contexts where it would make sense to use
nowritebarrierrec, this commit teaches the nowritebarrierrec analysis
to stop at allocm.

Updates #10600.

Change-Id: I8499629461d4fe25712d861720dfe438df7ada9b
Reviewed-on: https://go-review.googlesource.com/17005
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Austin Clements 2015-11-17 17:28:35 -05:00
parent c84ae1c499
commit 402e37d4a9
2 changed files with 6 additions and 0 deletions
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3
src/cmd/compile/internal/gc/dcl.go
View File

@ -1575,6 +1575,9 @@ func (c *nowritebarrierrecChecker) visitcall(n *Node) {
if fn == nil || fn.Op != ONAME || fn.Class != PFUNC || fn.Name.Defn == nil {
return
}
if (compiling_runtime != 0 || fn.Sym.Pkg == Runtimepkg) && fn.Sym.Name == "allocm" {
return
}
defn := fn.Name.Defn
fnbest, ok := c.best[defn]

3
src/runtime/proc.go
View File

@ -1182,6 +1182,9 @@ type cgothreadstart struct {
// Allocate a new m unassociated with any thread.
// Can use p for allocation context if needed.
// fn is recorded as the new m's m.mstartfn.
//
// This function it known to the compiler to inhibit the
// go:nowritebarrierrec annotation because it uses P for allocation.
func allocm(_p_ *p, fn func()) *m {
_g_ := getg()
_g_.m.locks++ // disable GC because it can be called from sysmon