mirror of
https://github.com/golang/go.git
synced 2025-10-19 19:13:18 +00:00
[dev.regabi] cmd/compile: simplify and optimize reorder3
reorder3 is the code responsible for ensuring that evaluation of an N:N parallel assignment statement respects the order of evaluation rules specified for Go. This CL simplifies the code and improves it from an O(N^2) algorithm to O(N). Passes toolstash -cmp. Change-Id: I04cd31613af6924f637b042be8ad039ec6a924c2 Reviewed-on: https://go-review.googlesource.com/c/go/+/280437 Trust: Matthew Dempsky <mdempsky@google.com> Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
This commit is contained in:
Matthew Dempsky
parent
e6c973198d
commit
4c215c4fa9
1 changed files with 85 additions and 152 deletions
|
|
@ -395,10 +395,35 @@ func ascompatet(nl ir.Nodes, nr *types.Type) []ir.Node {
|
|||
//
|
||||
// function calls have been removed.
|
||||
func reorder3(all []*ir.AssignStmt) []ir.Node {
|
||||
var assigned ir.NameSet
|
||||
var memWrite bool
|
||||
|
||||
// affected reports whether expression n could be affected by
|
||||
// the assignments applied so far.
|
||||
affected := func(n ir.Node) bool {
|
||||
return ir.Any(n, func(n ir.Node) bool {
|
||||
if n.Op() == ir.ONAME && assigned.Has(n.(*ir.Name)) {
|
||||
return true
|
||||
}
|
||||
if memWrite && readsMemory(n) {
|
||||
return true
|
||||
}
|
||||
return false
|
||||
})
|
||||
}
|
||||
|
||||
// If a needed expression may be affected by an
|
||||
// earlier assignment, make an early copy of that
|
||||
// expression and use the copy instead.
|
||||
var early []ir.Node
|
||||
save := func(np *ir.Node) {
|
||||
if n := *np; affected(n) {
|
||||
tmp := ir.Node(typecheck.Temp(n.Type()))
|
||||
as := typecheck.Stmt(ir.NewAssignStmt(base.Pos, tmp, n))
|
||||
early = append(early, as)
|
||||
*np = tmp
|
||||
}
|
||||
}
|
||||
|
||||
var mapinit ir.Nodes
|
||||
for i, n := range all {
|
||||
|
|
@ -407,19 +432,18 @@ func reorder3(all []*ir.AssignStmt) []ir.Node {
|
|||
// Save subexpressions needed on left side.
|
||||
// Drill through non-dereferences.
|
||||
for {
|
||||
switch ll := l; ll.Op() {
|
||||
case ir.ODOT:
|
||||
ll := ll.(*ir.SelectorExpr)
|
||||
l = ll.X
|
||||
continue
|
||||
case ir.OPAREN:
|
||||
ll := ll.(*ir.ParenExpr)
|
||||
l = ll.X
|
||||
continue
|
||||
case ir.OINDEX:
|
||||
ll := ll.(*ir.IndexExpr)
|
||||
switch ll := l.(type) {
|
||||
case *ir.IndexExpr:
|
||||
if ll.X.Type().IsArray() {
|
||||
ll.Index = reorder3save(ll.Index, all, i, &early)
|
||||
save(&ll.Index)
|
||||
l = ll.X
|
||||
continue
|
||||
}
|
||||
case *ir.ParenExpr:
|
||||
l = ll.X
|
||||
continue
|
||||
case *ir.SelectorExpr:
|
||||
if ll.Op() == ir.ODOT {
|
||||
l = ll.X
|
||||
continue
|
||||
}
|
||||
|
|
@ -427,31 +451,42 @@ func reorder3(all []*ir.AssignStmt) []ir.Node {
|
|||
break
|
||||
}
|
||||
|
||||
var name *ir.Name
|
||||
switch l.Op() {
|
||||
default:
|
||||
base.Fatalf("reorder3 unexpected lvalue %v", l.Op())
|
||||
|
||||
case ir.ONAME:
|
||||
break
|
||||
name = l.(*ir.Name)
|
||||
|
||||
case ir.OINDEX, ir.OINDEXMAP:
|
||||
l := l.(*ir.IndexExpr)
|
||||
l.X = reorder3save(l.X, all, i, &early)
|
||||
l.Index = reorder3save(l.Index, all, i, &early)
|
||||
save(&l.X)
|
||||
save(&l.Index)
|
||||
if l.Op() == ir.OINDEXMAP {
|
||||
all[i] = convas(all[i], &mapinit)
|
||||
}
|
||||
|
||||
case ir.ODEREF:
|
||||
l := l.(*ir.StarExpr)
|
||||
l.X = reorder3save(l.X, all, i, &early)
|
||||
save(&l.X)
|
||||
case ir.ODOTPTR:
|
||||
l := l.(*ir.SelectorExpr)
|
||||
l.X = reorder3save(l.X, all, i, &early)
|
||||
save(&l.X)
|
||||
}
|
||||
|
||||
// Save expression on right side.
|
||||
all[i].Y = reorder3save(all[i].Y, all, i, &early)
|
||||
save(&all[i].Y)
|
||||
|
||||
if name == nil || name.Addrtaken() || name.Class_ == ir.PEXTERN || name.Class_ == ir.PAUTOHEAP {
|
||||
memWrite = true
|
||||
continue
|
||||
}
|
||||
if ir.IsBlank(name) {
|
||||
// We can ignore assignments to blank.
|
||||
continue
|
||||
}
|
||||
assigned.Add(name)
|
||||
}
|
||||
|
||||
early = append(mapinit, early...)
|
||||
|
|
@ -461,109 +496,13 @@ func reorder3(all []*ir.AssignStmt) []ir.Node {
|
|||
return early
|
||||
}
|
||||
|
||||
// if the evaluation of *np would be affected by the
|
||||
// assignments in all up to but not including the ith assignment,
|
||||
// copy into a temporary during *early and
|
||||
// replace *np with that temp.
|
||||
// The result of reorder3save MUST be assigned back to n, e.g.
|
||||
// n.Left = reorder3save(n.Left, all, i, early)
|
||||
func reorder3save(n ir.Node, all []*ir.AssignStmt, i int, early *[]ir.Node) ir.Node {
|
||||
if !aliased(n, all[:i]) {
|
||||
return n
|
||||
}
|
||||
|
||||
q := ir.Node(typecheck.Temp(n.Type()))
|
||||
as := typecheck.Stmt(ir.NewAssignStmt(base.Pos, q, n))
|
||||
*early = append(*early, as)
|
||||
return q
|
||||
}
|
||||
|
||||
// Is it possible that the computation of r might be
|
||||
// affected by assignments in all?
|
||||
func aliased(r ir.Node, all []*ir.AssignStmt) bool {
|
||||
if r == nil {
|
||||
return false
|
||||
}
|
||||
|
||||
// Treat all fields of a struct as referring to the whole struct.
|
||||
// We could do better but we would have to keep track of the fields.
|
||||
for r.Op() == ir.ODOT {
|
||||
r = r.(*ir.SelectorExpr).X
|
||||
}
|
||||
|
||||
// Look for obvious aliasing: a variable being assigned
|
||||
// during the all list and appearing in n.
|
||||
// Also record whether there are any writes to addressable
|
||||
// memory (either main memory or variables whose addresses
|
||||
// have been taken).
|
||||
memwrite := false
|
||||
for _, as := range all {
|
||||
// We can ignore assignments to blank.
|
||||
if ir.IsBlank(as.X) {
|
||||
continue
|
||||
}
|
||||
|
||||
lv := ir.OuterValue(as.X)
|
||||
if lv.Op() != ir.ONAME {
|
||||
memwrite = true
|
||||
continue
|
||||
}
|
||||
l := lv.(*ir.Name)
|
||||
|
||||
switch l.Class_ {
|
||||
default:
|
||||
base.Fatalf("unexpected class: %v, %v", l, l.Class_)
|
||||
|
||||
case ir.PAUTOHEAP, ir.PEXTERN:
|
||||
memwrite = true
|
||||
continue
|
||||
|
||||
case ir.PAUTO, ir.PPARAM, ir.PPARAMOUT:
|
||||
if l.Name().Addrtaken() {
|
||||
memwrite = true
|
||||
continue
|
||||
}
|
||||
|
||||
if refersToName(l, r) {
|
||||
// Direct hit: l appears in r.
|
||||
return true
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// The variables being written do not appear in r.
|
||||
// However, r might refer to computed addresses
|
||||
// that are being written.
|
||||
|
||||
// If no computed addresses are affected by the writes, no aliasing.
|
||||
if !memwrite {
|
||||
return false
|
||||
}
|
||||
|
||||
// If r does not refer to any variables whose addresses have been taken,
|
||||
// then the only possible writes to r would be directly to the variables,
|
||||
// and we checked those above, so no aliasing problems.
|
||||
if !anyAddrTaken(r) {
|
||||
return false
|
||||
}
|
||||
|
||||
// Otherwise, both the writes and r refer to computed memory addresses.
|
||||
// Assume that they might conflict.
|
||||
return true
|
||||
}
|
||||
|
||||
// anyAddrTaken reports whether the evaluation n,
|
||||
// which appears on the left side of an assignment,
|
||||
// may refer to variables whose addresses have been taken.
|
||||
func anyAddrTaken(n ir.Node) bool {
|
||||
return ir.Any(n, func(n ir.Node) bool {
|
||||
// readsMemory reports whether the evaluation n directly reads from
|
||||
// memory that might be written to indirectly.
|
||||
func readsMemory(n ir.Node) bool {
|
||||
switch n.Op() {
|
||||
case ir.ONAME:
|
||||
n := n.(*ir.Name)
|
||||
return n.Class_ == ir.PEXTERN || n.Class_ == ir.PAUTOHEAP || n.Name().Addrtaken()
|
||||
|
||||
case ir.ODOT: // but not ODOTPTR - should have been handled in aliased.
|
||||
base.Fatalf("anyAddrTaken unexpected ODOT")
|
||||
return n.Class_ == ir.PEXTERN || n.Class_ == ir.PAUTOHEAP || n.Addrtaken()
|
||||
|
||||
case ir.OADD,
|
||||
ir.OAND,
|
||||
|
|
@ -574,6 +513,7 @@ func anyAddrTaken(n ir.Node) bool {
|
|||
ir.OCONVIFACE,
|
||||
ir.OCONVNOP,
|
||||
ir.ODIV,
|
||||
ir.ODOT,
|
||||
ir.ODOTTYPE,
|
||||
ir.OLITERAL,
|
||||
ir.OLSH,
|
||||
|
|
@ -590,16 +530,9 @@ func anyAddrTaken(n ir.Node) bool {
|
|||
ir.OXOR:
|
||||
return false
|
||||
}
|
||||
|
||||
// Be conservative.
|
||||
return true
|
||||
})
|
||||
}
|
||||
|
||||
// refersToName reports whether r refers to name.
|
||||
func refersToName(name *ir.Name, r ir.Node) bool {
|
||||
return ir.Any(r, func(r ir.Node) bool {
|
||||
return r.Op() == ir.ONAME && r == name
|
||||
})
|
||||
}
|
||||
|
||||
// refersToCommonName reports whether any name
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue