core/vm: refactor memory resize

core/vm/memory.go

@@ -76,12 +76,15 @@ func (m *Memory) Set32(offset uint64, val *uint256.Int) {
 	val.PutUint256(m.store[offset:])
 }
 
-// Resize resizes the memory to size
 func (m *Memory) Resize(size uint64) {
 	if uint64(m.Len()) < size {
+		if uint64(cap(m.store)) > size {
+			m.store = m.store[:size]
+		} else {
 			m.store = append(m.store, make([]byte, size-uint64(m.Len()))...)
 		}
 	}
+}
 
 // GetCopy returns offset + size as a new slice
 func (m *Memory) GetCopy(offset, size uint64) (cpy []byte) {

core/vm/memory_test.go

@@ -83,3 +83,10 @@ func TestMemoryCopy(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkResize(b *testing.B) {
+	memory := NewMemory()
+	for i := range b.N {
+		memory.Resize(uint64(i))
+	}
+}