diff --git a/src/cmd/compile/internal/gc/popt.go b/src/cmd/compile/internal/gc/popt.go
index 4d71ab643da..b7082228455 100644
--- a/src/cmd/compile/internal/gc/popt.go
+++ b/src/cmd/compile/internal/gc/popt.go
@@ -241,6 +241,19 @@ var flowmark int
 // will not have flow graphs and consequently will not be optimized.
 const MaxFlowProg = 50000
 
+var ffcache []Flow // reusable []Flow, to reduce allocation
+
+func growffcache(n int) {
+	if n > cap(ffcache) {
+		n = (n * 5) / 4
+		if n > MaxFlowProg {
+			n = MaxFlowProg
+		}
+		ffcache = make([]Flow, n)
+	}
+	ffcache = ffcache[:n]
+}
+
 func Flowstart(firstp *obj.Prog, newData func() interface{}) *Graph {
 	// Count and mark instructions to annotate.
 	nf := 0
@@ -268,7 +281,9 @@ func Flowstart(firstp *obj.Prog, newData func() interface{}) *Graph {
 
 	// Allocate annotations and assign to instructions.
 	graph := new(Graph)
-	ff := make([]Flow, nf)
+
+	growffcache(nf)
+	ff := ffcache
 	start := &ff[0]
 	id := 0
 	var last *Flow
@@ -331,6 +346,10 @@ func Flowend(graph *Graph) {
 		f.Prog.Info.Flags = 0 // drop cached proginfo
 		f.Prog.Opt = nil
 	}
+	clear := ffcache[:graph.Num]
+	for i := range clear {
+		clear[i] = Flow{}
+	}
 }
 
 // find looping structure