cmd/compile: don't use statictmps for small object in slice literal
Fixes #21561
Change-Id: I89c59752060dd9570d17d73acbbaceaefce5d8ce
Reviewed-on: https://go-review.googlesource.com/c/go/+/197560
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index f36e271..bfd2ce2 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -29,6 +29,12 @@
// s := []byte("...") allocating [n]byte on the stack
// Note: the flag smallframes can update this value.
maxImplicitStackVarSize = int64(64 * 1024)
+
+ // smallArrayBytes is the maximum size of an array which is considered small.
+ // Small arrays will be initialized directly with a sequence of constant stores.
+ // Large arrays will be initialized by copying from a static temp.
+ // 256 bytes was chosen to minimize generated code + statictmp size.
+ smallArrayBytes = int64(256)
)
// isRuntimePkg reports whether p is package runtime.
diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go
index a6d13d1..96b3430 100644
--- a/src/cmd/compile/internal/gc/sinit.go
+++ b/src/cmd/compile/internal/gc/sinit.go
@@ -582,6 +582,16 @@
}
}
+func isSmallSliceLit(n *Node) bool {
+ if n.Op != OSLICELIT {
+ return false
+ }
+
+ r := n.Right
+
+ return smallintconst(r) && (n.Type.Elem().Width == 0 || r.Int64() <= smallArrayBytes/n.Type.Elem().Width)
+}
+
func slicelit(ctxt initContext, n *Node, var_ *Node, init *Nodes) {
// make an array type corresponding the number of elements we have
t := types.NewArray(n.Type.Elem(), n.Right.Int64())
@@ -639,7 +649,7 @@
var vstat *Node
mode := getdyn(n, true)
- if mode&initConst != 0 {
+ if mode&initConst != 0 && !isSmallSliceLit(n) {
vstat = staticname(t)
if ctxt == inInitFunction {
vstat.Name.SetReadonly(true)
diff --git a/test/codegen/slices.go b/test/codegen/slices.go
index fccd711..cf569e2 100644
--- a/test/codegen/slices.go
+++ b/test/codegen/slices.go
@@ -113,3 +113,54 @@
// amd64:-`TESTB`
_ = *p
}
+
+// ---------------------- //
+// Init slice literal //
+// ---------------------- //
+// See issue 21561
+func InitSmallSliceLiteral() []int {
+ // amd64:`MOVQ\t[$]42`
+ return []int{42}
+}
+
+func InitNotSmallSliceLiteral() []int {
+ // amd64:`MOVQ\t.*autotmp_`
+ return []int{
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ 42,
+ }
+}
