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runtime: split PCs out of scase

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Per-case PCs are only needed for race detector builds, so this allows
skipping allocating stack space for them for non-race builds.

It's possible to arrange the PCs and order arrays consecutively in
memory so that we could just reuse the order0 pointer to identify
both. However, there's more risk of that silently going wrong, so this
commit passes them as separate arguments for now. We can revisit this
in the future.

Updates #40410.

Change-Id: I8468bc25749e559891cb0cb007d1cc4a40fdd0f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/245124
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Matthew Dempsky 2020-07-27 15:20:18 -07:00
parent 8a984e8e3f
commit d36bc7d78a
4 changed files with 154 additions and 119 deletions
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18
src/cmd/compile/internal/gc/select.go
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@ -271,6 +271,14 @@ func walkselectcases(cases *Nodes) []*Node {
r = typecheck(r, ctxStmt)
init = append(init, r)
var pc0, pcs *Node
if flag_race {
pcs = temp(types.NewArray(types.Types[TUINTPTR], int64(n)))
pc0 = typecheck(nod(OADDR, nod(OINDEX, pcs, nodintconst(0)), nil), ctxExpr)
} else {
pc0 = nodnil()
}
// register cases
for i, cas := range cases.Slice() {
setlineno(cas)
@ -324,8 +332,8 @@ func walkselectcases(cases *Nodes) []*Node {
// TODO(mdempsky): There should be a cleaner way to
// handle this.
if instrumenting {
r = mkcall("selectsetpc", nil, nil, bytePtrToIndex(selv, int64(i)))
if flag_race {
r = mkcall("selectsetpc", nil, nil, nod(OADDR, nod(OINDEX, pcs, nodintconst(int64(i))), nil))
init = append(init, r)
}
}
@ -337,13 +345,16 @@ func walkselectcases(cases *Nodes) []*Node {
r = nod(OAS2, nil, nil)
r.List.Set2(chosen, recvOK)
fn := syslook("selectgo")
r.Rlist.Set1(mkcall1(fn, fn.Type.Results(), nil, bytePtrToIndex(selv, 0), bytePtrToIndex(order, 0), nodintconst(int64(n))))
r.Rlist.Set1(mkcall1(fn, fn.Type.Results(), nil, bytePtrToIndex(selv, 0), bytePtrToIndex(order, 0), pc0, nodintconst(int64(n))))
r = typecheck(r, ctxStmt)
init = append(init, r)
// selv and order are no longer alive after selectgo.
init = append(init, nod(OVARKILL, selv, nil))
init = append(init, nod(OVARKILL, order, nil))
if flag_race {
init = append(init, nod(OVARKILL, pcs, nil))
}
// dispatch cases
for i, cas := range cases.Slice() {
@ -385,7 +396,6 @@ func scasetype() *types.Type {
namedfield("c", types.Types[TUNSAFEPTR]),
namedfield("elem", types.Types[TUNSAFEPTR]),
namedfield("kind", types.Types[TUINT16]),
namedfield("pc", types.Types[TUINTPTR]),
})
scase.SetNoalg(true)
}