cmd/compile: reduce slice header allocation when parsing := assignments

The colas function allocates 2 slice headers in each call (via Nodes.Set)
only to throw away those slice headers in the common case where both the
lhs and rhs in "lhs := rhs" have length 1.

Avoid the Nodes.Set calls in those cases. For make.bash, this eliminates
~63,000 slice header allocations.

Also: Minor cleanups in colasdefn.

Change-Id: Ib114a67c3adeb8821868bd71a5e0f5e2e19fcd4f
Reviewed-on: https://go-review.googlesource.com/21170
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/gc/alg.go b/src/cmd/compile/internal/gc/alg.go
index d07a1529d0ac1065fd556e2a7b456feafce7ca16..a23e38d2be91dd647ae1d92360099f57a8df2023 100644 (file)
--- a/src/cmd/compile/internal/gc/alg.go
+++ b/src/cmd/compile/internal/gc/alg.go
@@ -210,7 +210,7 @@ func genhash(sym *Sym, t *Type) {
                ni.Type = Types[TINT]
                n.List.Set1(ni)
                n.Colas = true
-               colasdefn(n.List, n)
+               colasdefn(n.List.Slice(), n)
                ni = n.List.First()
 
                // h = hashel(&p[i], h)
@@ -390,7 +390,7 @@ func geneq(sym *Sym, t *Type) {
                ni.Type = Types[TINT]
                nrange.List.Set1(ni)
                nrange.Colas = true
-               colasdefn(nrange.List, nrange)
+               colasdefn(nrange.List.Slice(), nrange)
                ni = nrange.List.First()
 
                // if p[i] != q[i] { return false }

diff --git a/src/cmd/compile/internal/gc/dcl.go b/src/cmd/compile/internal/gc/dcl.go
index c55d0e34cc92bdb2659f7dfc2f8bcee7b37f948d..a04fde1831891d292fb42c409865921148a65aa0 100644 (file)
--- a/src/cmd/compile/internal/gc/dcl.go
+++ b/src/cmd/compile/internal/gc/dcl.go
@@ -432,18 +432,15 @@ func colasname(n *Node) bool {
        return false
 }
 
-func colasdefn(left Nodes, defn *Node) {
-       for _, n1 := range left.Slice() {
-               if n1.Sym != nil {
-                       n1.Sym.Flags |= SymUniq
+func colasdefn(left []*Node, defn *Node) {
+       for _, n := range left {
+               if n.Sym != nil {
+                       n.Sym.Flags |= SymUniq
                }
        }
 
-       nnew := 0
-       nerr := 0
-       var n *Node
-       for i2, n2 := range left.Slice() {
-               n = n2
+       var nnew, nerr int
+       for i, n := range left {
                if isblank(n) {
                        continue
                }
@@ -470,7 +467,7 @@ func colasdefn(left Nodes, defn *Node) {
                declare(n, dclcontext)
                n.Name.Defn = defn
                defn.Ninit.Append(Nod(ODCL, n, nil))
-               left.SetIndex(i2, n)
+               left[i] = n
        }
 
        if nnew == 0 && nerr == 0 {
@@ -478,24 +475,21 @@ func colasdefn(left Nodes, defn *Node) {
        }
 }
 
-func colas(left []*Node, right []*Node, lno int32) *Node {
-       as := Nod(OAS2, nil, nil)
-       as.List.Set(left)
-       as.Rlist.Set(right)
-       as.Colas = true
-       as.Lineno = lno
-       colasdefn(as.List, as)
-
-       // make the tree prettier; not necessary
-       if as.List.Len() == 1 && as.Rlist.Len() == 1 {
-               as.Left = as.List.First()
-               as.Right = as.Rlist.First()
-               as.List.Set(nil)
-               as.Rlist.Set(nil)
-               as.Op = OAS
+func colas(left, right []*Node, lno int32) *Node {
+       n := Nod(OAS, nil, nil) // assume common case
+       n.Colas = true
+       n.Lineno = lno     // set before calling colasdefn for correct error line
+       colasdefn(left, n) // modifies left, call before using left[0] in common case
+       if len(left) == 1 && len(right) == 1 {
+               // common case
+               n.Left = left[0]
+               n.Right = right[0]
+       } else {
+               n.Op = OAS2
+               n.List.Set(left)
+               n.Rlist.Set(right)
        }
-
-       return as
+       return n
 }
 
 // declare the arguments in an

diff --git a/src/cmd/compile/internal/gc/parser.go b/src/cmd/compile/internal/gc/parser.go
index db9d4c9ee5cfc8e0d17fd2a79f44cf292a3aba48..892dd5969a837a2ef9a71afe51fcbee9f3f1f33f 100644 (file)
--- a/src/cmd/compile/internal/gc/parser.go
+++ b/src/cmd/compile/internal/gc/parser.go
@@ -636,7 +636,7 @@ func (p *parser) simple_stmt(labelOk, rangeOk bool) *Node {
                        r := Nod(ORANGE, nil, p.expr())
                        r.List.Set(lhs)
                        r.Colas = true
-                       colasdefn(r.List, r)
+                       colasdefn(lhs, r)
                        return r
                }