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cmd/compile: add size hint to map literal allocations

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Might as well tell the runtime how large the map is going to be.
This avoids grow work and allocations while the map is being built.

Will wait for 1.8.

Fixes #15880
Fixes #16279

Change-Id: I377e3e5ec1e2e76ea2a50cc00810adda20ad0e79
Reviewed-on: https://go-review.googlesource.com/23558
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Keith Randall 2016-05-29 11:16:13 -07:00
parent 35e25ef62e
commit 1faea596e4
2 changed files with 6 additions and 1 deletions
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2
src/cmd/compile/internal/gc/sinit.go
View file

@ -866,7 +866,7 @@ func maplit(ctxt int, n *Node, var_ *Node, init *Nodes) {
nerr := nerrors nerr := nerrors
a := Nod(OMAKE, nil, nil) a := Nod(OMAKE, nil, nil)
a.List.Set1(typenod(n.Type)) a.List.Set2(typenod(n.Type), Nodintconst(int64(len(n.List.Slice()))))
litas(var_, a, init) litas(var_, a, init)
// count the initializers // count the initializers

5
src/cmd/compile/internal/gc/syntax.go
View file

@ -545,6 +545,11 @@ func (n *Nodes) Set1(node *Node) {
n.slice = &[]*Node{node} n.slice = &[]*Node{node}
} }
// Set2 sets n to a slice containing two nodes.
func (n *Nodes) Set2(n1, n2 *Node) {
n.slice = &[]*Node{n1, n2}
}
// MoveNodes sets n to the contents of n2, then clears n2. // MoveNodes sets n to the contents of n2, then clears n2.
func (n *Nodes) MoveNodes(n2 *Nodes) { func (n *Nodes) MoveNodes(n2 *Nodes) {
n.slice = n2.slice n.slice = n2.slice