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compiler: reimplement for-range loops without syscalls

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System.Enumerator.Next costs 1_000_000 gas which is rather big for a
single iteration. Reimplement this by saving current counters on stack.
This approach will use 2 PICKITEMS (270_000 gas) for maps, which is
still cheaper that *.Next syscall.
This commit is contained in:
Evgenii Stratonikov 2020-06-19 17:14:00 +03:00
parent da2d96d42f
commit 3729865860
1 changed files with 41 additions and 9 deletions
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50
pkg/compiler/codegen.go
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@ -900,23 +900,47 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
c.currentSwitch = label
ast.Walk(c, n.X)
emit.Syscall(c.prog.BinWriter, "System.Iterator.Create")
c.pushStackLabel(label, 1)
// Implementation is a bit different for slices and maps:
// For slices we iterate index from 0 to len-1, storing array, len and index on stack.
// For maps we iterate index from 0 to len-1, storing map, keyarray, size and index on stack.
_, isMap := c.typeOf(n.X).Underlying().(*types.Map)
emit.Opcode(c.prog.BinWriter, opcode.DUP)
if isMap {
emit.Opcode(c.prog.BinWriter, opcode.KEYS)
emit.Opcode(c.prog.BinWriter, opcode.DUP)
}
emit.Opcode(c.prog.BinWriter, opcode.SIZE)
emit.Opcode(c.prog.BinWriter, opcode.PUSH0)
stackSize := 3 // slice, len(slice), index
if isMap {
stackSize++ // map, keys, len(keys), index in keys
}
c.pushStackLabel(label, stackSize)
c.setLabel(start)
emit.Opcode(c.prog.BinWriter, opcode.DUP)
emit.Syscall(c.prog.BinWriter, "System.Enumerator.Next")
emit.Jmp(c.prog.BinWriter, opcode.JMPIFNOTL, end)
emit.Opcode(c.prog.BinWriter, opcode.OVER)
emit.Opcode(c.prog.BinWriter, opcode.OVER)
emit.Jmp(c.prog.BinWriter, opcode.JMPLEL, end)
if n.Key != nil {
emit.Opcode(c.prog.BinWriter, opcode.DUP)
emit.Syscall(c.prog.BinWriter, "System.Iterator.Key")
if isMap {
c.rangeLoadKey()
} else {
emit.Opcode(c.prog.BinWriter, opcode.DUP)
}
c.emitStoreVar(n.Key.(*ast.Ident).Name)
}
if n.Value != nil {
emit.Opcode(c.prog.BinWriter, opcode.DUP)
emit.Syscall(c.prog.BinWriter, "System.Enumerator.Value")
c.rangeLoadKey()
if isMap {
// we have loaded only key from key array, now load value
emit.Int(c.prog.BinWriter, 4)
emit.Opcode(c.prog.BinWriter, opcode.PICK) // load map itself (+1 because key was pushed)
emit.Opcode(c.prog.BinWriter, opcode.SWAP) // key should be on top
emit.Opcode(c.prog.BinWriter, opcode.PICKITEM)
}
c.emitStoreVar(n.Value.(*ast.Ident).Name)
}
@ -924,6 +948,7 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
c.setLabel(post)
emit.Opcode(c.prog.BinWriter, opcode.INC)
emit.Jmp(c.prog.BinWriter, opcode.JMPL, start)
c.setLabel(end)
@ -945,6 +970,13 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
return c
}
func (c *codegen) rangeLoadKey() {
emit.Int(c.prog.BinWriter, 2)
emit.Opcode(c.prog.BinWriter, opcode.PICK) // load keys
emit.Opcode(c.prog.BinWriter, opcode.OVER) // load index in key array
emit.Opcode(c.prog.BinWriter, opcode.PICKITEM)
}
func isFallthroughStmt(c ast.Node) bool {
s, ok := c.(*ast.BranchStmt)
return ok && s.Tok == token.FALLTHROUGH