cmd/compile: eliminate copy for static literals
*p = [5]byte{1,2,3,4,5}
First we allocate a global containing the RHS. Then we copy
that global to a local stack variable, and then copy that local
stack variable to *p. The intermediate copy is unnecessary.
Note that this only works if the RHS is completely constant.
If the code was:
*p = [5]byte{1,2,x,4,5}
this optimization doesn't apply as we have to construct the
RHS on the stack before copying it to *p.
Fixes #12841
Change-Id: I7cd0404ecc7a2d1750cbd8fe1222dba0fa44611f
Reviewed-on: https://go-review.googlesource.com/22192
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go
index 85ef78b..1021609 100644
--- a/src/cmd/compile/internal/gc/sinit.go
+++ b/src/cmd/compile/internal/gc/sinit.go
@@ -563,6 +563,32 @@
return mode
}
+// isStaticCompositeLiteral reports whether n is a compile-time constant.
+// n must be a struct or array literal.
+func isStaticCompositeLiteral(n *Node) bool {
+ for _, r := range n.List.Slice() {
+ if r.Op != OKEY {
+ Fatalf("isStaticCompositeLiteral: rhs not OKEY: %v", r)
+ }
+ index := r.Left
+ if n.Op == OARRAYLIT && index.Op != OLITERAL {
+ return false
+ }
+ value := r.Right
+ switch value.Op {
+ case OSTRUCTLIT, OARRAYLIT:
+ if !isStaticCompositeLiteral(value) {
+ return false
+ }
+ default:
+ if value.Op != OLITERAL {
+ return false
+ }
+ }
+ }
+ return true
+}
+
func structlit(ctxt int, pass int, n *Node, var_ *Node, init *Nodes) {
for _, r := range n.List.Slice() {
if r.Op != OKEY {
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index 78bad8d..1a15bd9 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -1531,6 +1531,19 @@
n = r
case OARRAYLIT, OMAPLIT, OSTRUCTLIT, OPTRLIT:
+ if (n.Op == OSTRUCTLIT || (n.Op == OARRAYLIT && !n.Type.IsSlice())) && isStaticCompositeLiteral(n) {
+ // n can be directly represented in the read-only data section.
+ // Make direct reference to the static data. See issue 12841.
+ vstat := staticname(n.Type, 0)
+ if n.Op == OSTRUCTLIT {
+ structlit(0, 1, n, vstat, init)
+ } else {
+ arraylit(0, 1, n, vstat, init)
+ }
+ n = vstat
+ n = typecheck(n, Erv)
+ break
+ }
var_ := temp(n.Type)
anylit(0, n, var_, init)
n = var_
