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cmd/compile, runtime: add go:yeswritebarrierrec pragma

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This pragma cancels the effect of go:nowritebarrierrec. This is useful
in the scheduler because there are places where we enter a function
without a valid P (and hence cannot have write barriers), but then
obtain a P. This allows us to annotate the function with
go:nowritebarrierrec and split out the part after we've obtained a P
into a go:yeswritebarrierrec function.

Change-Id: Ic8ce4b6d3c074a1ecd8280ad90eaf39f0ffbcc2a
Reviewed-on: https://go-review.googlesource.com/30938
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Austin Clements 2016-10-10 16:46:28 -04:00
parent 6347367be3
commit a9e6cebde2
6 changed files with 194 additions and 34 deletions
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11
src/cmd/compile/internal/gc/dcl.go
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@ -1317,7 +1317,7 @@ func checknowritebarrierrec() {
visitBottomUp(xtop, func(list []*Node, recursive bool) {
// Functions with write barriers have depth 0.
for _, n := range list {
if n.Func.WBLineno != 0 {
if n.Func.WBLineno != 0 && n.Func.Pragma&Yeswritebarrierrec == 0 {
c.best[n] = nowritebarrierrecCall{target: nil, depth: 0, lineno: n.Func.WBLineno}
}
}
@ -1329,6 +1329,12 @@ func checknowritebarrierrec() {
for _ = range list {
c.stable = false
for _, n := range list {
if n.Func.Pragma&Yeswritebarrierrec != 0 {
// Don't propagate write
// barrier up to a
// yeswritebarrierrec function.
continue
}
if n.Func.WBLineno == 0 {
c.curfn = n
c.visitcodelist(n.Nbody)
@ -1393,9 +1399,6 @@ func (c *nowritebarrierrecChecker) visitcall(n *Node) {
if fn == nil || fn.Op != ONAME || fn.Class != PFUNC || fn.Name.Defn == nil {
return
}
if (compiling_runtime || fn.Sym.Pkg == Runtimepkg) && fn.Sym.Name == "allocm" {
return
}
defn := fn.Name.Defn
fnbest, ok := c.best[defn]