cmd/compile: aggregate scalar allocations for heap escapes

If multiple small scalars escape to the heap, allocate them together
with a single allocation. They are going to be aggregated together
in the tiny allocator anyway, might as well do just one runtime call.

Change-Id: I4317e29235af63de378a26436a18d7fb0c39e41f
Reviewed-on: https://go-review.googlesource.com/c/go/+/648536
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/test/locals_test.go b/src/cmd/compile/internal/test/locals_test.go
new file mode 100644
index 0000000000..a5eafc6116
--- /dev/null
+++ b/src/cmd/compile/internal/test/locals_test.go
@@ -0,0 +1,76 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package test
+
+import "testing"
+
+func locals() {
+	var x int64
+	var y int32
+	var z int16
+	var w int8
+	sink64 = &x
+	sink32 = &y
+	sink16 = &z
+	sink8 = &w
+}
+
+//go:noinline
+func args(x int64, y int32, z int16, w int8) {
+	sink64 = &x
+	sink32 = &y
+	sink16 = &z
+	sink8 = &w
+
+}
+
+//go:noinline
+func half(x int64, y int16) {
+	var z int32
+	var w int8
+	sink64 = &x
+	sink16 = &y
+	sink32 = &z
+	sink8 = &w
+}
+
+//go:noinline
+func closure() func() {
+	var x int64
+	var y int32
+	var z int16
+	var w int8
+	_, _, _, _ = x, y, z, w
+	return func() {
+		x = 1
+		y = 2
+		z = 3
+		w = 4
+	}
+}
+
+var sink64 *int64
+var sink32 *int32
+var sink16 *int16
+var sink8 *int8
+
+func TestLocalAllocations(t *testing.T) {
+	type test struct {
+		name string
+		f    func()
+		want int
+	}
+	for _, tst := range []test{
+		{"locals", locals, 1},
+		{"args", func() { args(1, 2, 3, 4) }, 1},
+		{"half", func() { half(1, 2) }, 1},
+		{"closure", func() { _ = closure() }, 2},
+	} {
+		allocs := testing.AllocsPerRun(100, tst.f)
+		if allocs != float64(tst.want) {
+			t.Errorf("test %s uses %v allocs, want %d", tst.name, allocs, tst.want)
+		}
+	}
+}