#
#
# The Nim Compiler
# (c) Copyright 2017 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
## Injects destructor calls into Nim code as well as
## an optimizer that optimizes copies to moves. This is implemented as an
## AST to AST transformation so that every backend benefits from it.
## Rules for destructor injections:
##
## foo(bar(X(), Y()))
## X and Y get destroyed after bar completes:
##
## foo( (tmpX = X(); tmpY = Y(); tmpBar = bar(tmpX, tmpY);
## destroy(tmpX); destroy(tmpY);
## tmpBar))
## destroy(tmpBar)
##
## var x = f()
## body
##
## is the same as:
##
## var x;
## try:
## move(x, f())
## finally:
## destroy(x)
##
## But this really just an optimization that tries to avoid to
## introduce too many temporaries, the 'destroy' is caused by
## the 'f()' call. No! That is not true for 'result = f()'!
##
## x = y where y is read only once
## is the same as: move(x, y)
##
## Actually the more general rule is: The *last* read of ``y``
## can become a move if ``y`` is the result of a construction.
##
## We also need to keep in mind here that the number of reads is
## control flow dependent:
## let x = foo()
## while true:
## y = x # only one read, but the 2nd iteration will fail!
## This also affects recursions! Only usages that do not cross
## a loop boundary (scope) and are not used in function calls
## are safe.
##
##
## x = f() is the same as: move(x, f())
##
## x = y
## is the same as: copy(x, y)
##
## Reassignment works under this scheme:
## var x = f()
## x = y
##
## is the same as:
##
## var x;
## try:
## move(x, f())
## copy(x, y)
## finally:
## destroy(x)
##
## result = f() must not destroy 'result'!
##
## The produced temporaries clutter up the code and might lead to
## inefficiencies. A better strategy is to collect all the temporaries
## in a single object that we put into a single try-finally that
## surrounds the proc body. This means the code stays quite efficient
## when compiled to C. In fact, we do the same for variables, so
## destructors are called when the proc returns, not at scope exit!
## This makes certains idioms easier to support. (Taking the slice
## of a temporary object.)
##
## foo(bar(X(), Y()))
## X and Y get destroyed after bar completes:
##
## var tmp: object
## foo( (move tmp.x, X(); move tmp.y, Y(); tmp.bar = bar(tmpX, tmpY);
## tmp.bar))
## destroy(tmp.bar)
## destroy(tmp.x); destroy(tmp.y)
##
##[
From https://github.com/nim-lang/Nim/wiki/Destructors
Rule Pattern Transformed into
---- ------- ----------------
1.1 var x: T; stmts var x: T; try stmts
finally: `=destroy`(x)
1.2 var x: sink T; stmts var x: sink T; stmts; ensureEmpty(x)
2 x = f() `=sink`(x, f())
3 x = lastReadOf z `=sink`(x, z); wasMoved(z)
4.1 y = sinkParam `=sink`(y, sinkParam)
4.2 x = y `=`(x, y) # a copy
5.1 f_sink(g()) f_sink(g())
5.2 f_sink(y) f_sink(copy y); # copy unless we can see it's the last read
5.3 f_sink(move y) f_sink(y); wasMoved(y) # explicit moves empties 'y'
5.4 f_noSink(g()) var tmp = bitwiseCopy(g()); f(tmp); `=destroy`(tmp)
Remarks: Rule 1.2 is not yet implemented because ``sink`` is currently
not allowed as a local variable.
``move`` builtin needs to be implemented.
]##
import
intsets, ast, astalgo, msgs, renderer, magicsys, types, idents, trees,
strutils, options, dfa, lowerings, tables, modulegraphs, msgs,
lineinfos, parampatterns
const
InterestingSyms = {skVar, skResult, skLet}
type
Con = object
owner: PSym
g: ControlFlowGraph
jumpTargets: IntSet
destroys, topLevelVars: PNode
graph: ModuleGraph
emptyNode: PNode
otherRead: PNode
proc isLastRead(s: PSym; c: var Con; pc, comesFrom: int): int =
var pc = pc
while pc < c.g.len:
case c.g[pc].kind
of def:
if c.g[pc].sym == s:
# the path lead to a redefinition of 's' --> abandon it.
return high(int)
inc pc
of use:
if c.g[pc].sym == s:
c.otherRead = c.g[pc].n
return -1
inc pc
of goto:
pc = pc + c.g[pc].dest
of fork:
# every branch must lead to the last read of the location:
var variantA = isLastRead(s, c, pc+1, pc)
if variantA < 0: return -1
let variantB = isLastRead(s, c, pc + c.g[pc].dest, pc)
if variantB < 0: return -1
elif variantA == high(int):
variantA = variantB
pc = variantA
of InstrKind.join:
let dest = pc + c.g[pc].dest
if dest == comesFrom: return pc + 1
inc pc
return pc
proc isLastRead(n: PNode; c: var Con): bool =
# first we need to search for the instruction that belongs to 'n':
doAssert n.kind == nkSym
c.otherRead = nil
var instr = -1
for i in 0..<c.g.len:
if c.g[i].n == n:
if instr < 0:
instr = i
break
if instr < 0: return false
# we go through all paths beginning from 'instr+1' and need to
# ensure that we don't find another 'use X' instruction.
if instr+1 >= c.g.len: return true
when true:
result = isLastRead(n.sym, c, instr+1, -1) >= 0
else:
let s = n.sym
var pcs: seq[int] = @[instr+1]
var takenGotos: IntSet
var takenForks = initIntSet()
while pcs.len > 0:
var pc = pcs.pop
takenGotos = initIntSet()
while pc < c.g.len:
case c.g[pc].kind
of def:
if c.g[pc].sym == s:
# the path lead to a redefinition of 's' --> abandon it.
break
inc pc
of use:
if c.g[pc].sym == s:
c.otherRead = c.g[pc].n
return false
inc pc
of goto:
# we must leave endless loops eventually:
if not takenGotos.containsOrIncl(pc):
pc = pc + c.g[pc].dest
else:
inc pc
of fork:
# we follow the next instruction but push the dest onto our "work" stack:
if not takenForks.containsOrIncl(pc):
pcs.add pc + c.g[pc].dest
inc pc
of InstrKind.join:
inc pc
#echo c.graph.config $ n.info, " last read here!"
return true
template interestingSym(s: PSym): bool =
s.owner == c.owner and s.kind in InterestingSyms and hasDestructor(s.typ)
template isUnpackedTuple(s: PSym): bool =
## we move out all elements of unpacked tuples,
## hence unpacked tuples themselves don't need to be destroyed
s.kind == skTemp and s.typ.kind == tyTuple
proc patchHead(n: PNode) =
if n.kind in nkCallKinds and n[0].kind == nkSym and n.len > 1:
let s = n[0].sym
if s.name.s[0] == '=' and s.name.s in ["=sink", "=", "=destroy"]:
if sfFromGeneric in s.flags:
excl(s.flags, sfFromGeneric)
patchHead(s.getBody)
let t = n[1].typ.skipTypes({tyVar, tyLent, tyGenericInst, tyAlias, tySink, tyInferred})
template patch(op, field) =
if s.name.s == op and field != nil and field != s:
n.sons[0].sym = field
patch "=sink", t.sink
patch "=", t.assignment
patch "=destroy", t.destructor
for x in n:
patchHead(x)
proc patchHead(s: PSym) =
if sfFromGeneric in s.flags:
# do not patch the builtin type bound operators for seqs:
let dest = s.typ.sons[1].skipTypes(abstractVar)
if dest.kind != tySequence:
patchHead(s.ast[bodyPos])
proc checkForErrorPragma(c: Con; t: PType; ri: PNode; opname: string) =
var m = "'" & opname & "' is not available for type <" & typeToString(t) & ">"
if opname == "=" and ri != nil:
m.add "; requires a copy because it's not the last read of '"
m.add renderTree(ri)
m.add '\''
if c.otherRead != nil:
m.add "; another read is done here: "
m.add c.graph.config $ c.otherRead.info
localError(c.graph.config, ri.info, errGenerated, m)
proc makePtrType(c: Con, baseType: PType): PType =
result = newType(tyPtr, c.owner)
addSonSkipIntLit(result, baseType)
template genOp(opr, opname, ri) =
let op = opr
if op == nil:
globalError(c.graph.config, dest.info, "internal error: '" & opname &
"' operator not found for type " & typeToString(t))
elif op.ast[genericParamsPos].kind != nkEmpty:
globalError(c.graph.config, dest.info, "internal error: '" & opname &
"' operator is generic")
patchHead op
if sfError in op.flags: checkForErrorPragma(c, t, ri, opname)
let addrExp = newNodeIT(nkHiddenAddr, dest.info, makePtrType(c, dest.typ))
addrExp.add(dest)
result = newTree(nkCall, newSymNode(op), addrExp)
proc genSink(c: Con; t: PType; dest, ri: PNode): PNode =
when false:
if t.kind != tyString:
echo "this one ", c.graph.config$dest.info, " for ", typeToString(t, preferDesc)
debug t.sink.typ.sons[2]
echo t.sink.id, " owner ", t.id
quit 1
let t = t.skipTypes({tyGenericInst, tyAlias, tySink})
genOp(if t.sink != nil: t.sink else: t.assignment, "=sink", ri)
proc genCopy(c: Con; t: PType; dest, ri: PNode): PNode =
let t = t.skipTypes({tyGenericInst, tyAlias, tySink})
genOp(t.assignment, "=", ri)
proc genDestroy(c: Con; t: PType; dest: PNode): PNode =
let t = t.skipTypes({tyGenericInst, tyAlias, tySink})
genOp(t.destructor, "=destroy", nil)
proc addTopVar(c: var Con; v: PNode) =
c.topLevelVars.add newTree(nkIdentDefs, v, c.emptyNode, c.emptyNode)
proc getTemp(c: var Con; typ: PType; info: TLineInfo): PNode =
let sym = newSym(skTemp, getIdent(c.graph.cache, ":tmpD"), c.owner, info)
sym.typ = typ
result = newSymNode(sym)
c.addTopVar(result)
proc p(n: PNode; c: var Con): PNode
template recurse(n, dest) =
for i in 0..<n.len:
dest.add p(n[i], c)
proc isSinkParam(s: PSym): bool {.inline.} =
result = s.kind == skParam and s.typ.kind == tySink
proc genMagicCall(n: PNode; c: var Con; magicname: string; m: TMagic): PNode =
result = newNodeI(nkCall, n.info)
result.add(newSymNode(createMagic(c.graph, magicname, m)))
result.add n
proc genWasMoved(n: PNode; c: var Con): PNode =
# The mWasMoved builtin does not take the address.
result = genMagicCall(n, c, "wasMoved", mWasMoved)
proc destructiveMoveVar(n: PNode; c: var Con): PNode =
# generate: (let tmp = v; reset(v); tmp)
# XXX: Strictly speaking we can only move if there is a ``=sink`` defined
# or if no ``=sink`` is defined and also no assignment.
result = newNodeIT(nkStmtListExpr, n.info, n.typ)
var temp = newSym(skLet, getIdent(c.graph.cache, "blitTmp"), c.owner, n.info)
temp.typ = n.typ
var v = newNodeI(nkLetSection, n.info)
let tempAsNode = newSymNode(temp)
var vpart = newNodeI(nkIdentDefs, tempAsNode.info, 3)
vpart.sons[0] = tempAsNode
vpart.sons[1] = c.emptyNode
vpart.sons[2] = n
add(v, vpart)
result.add v
result.add genWasMoved(n, c)
result.add tempAsNode
proc sinkParamIsLastReadCheck(c: var Con, s: PNode) =
assert s.kind == nkSym and s.sym.kind == skParam
if not isLastRead(s, c):
localError(c.graph.config, c.otherRead.info, "sink parameter `" & $s.sym.name.s &
"` is already consumed at " & toFileLineCol(c. graph.config, s.info))
proc passCopyToSink(n: PNode; c: var Con): PNode =
result = newNodeIT(nkStmtListExpr, n.info, n.typ)
let tmp = getTemp(c, n.typ, n.info)
if hasDestructor(n.typ):
var m = genCopy(c, n.typ, tmp, n)
m.add p(n, c)
result.add m
if isLValue(n):
message(c.graph.config, n.info, hintPerformance,
("passing '$1' to a sink parameter introduces an implicit copy; " &
"use 'move($1)' to prevent it") % $n)
else:
result.add newTree(nkAsgn, tmp, p(n, c))
result.add tmp
proc pArg(arg: PNode; c: var Con; isSink: bool): PNode =
template pArgIfTyped(arg_part: PNode): PNode =
# typ is nil if we are in if/case expr branch with noreturn
if arg_part.typ == nil: p(arg_part, c)
else: pArg(arg_part, c, isSink)
if isSink:
if arg.kind in nkCallKinds:
# recurse but skip the call expression in order to prevent
# destructor injections: Rule 5.1 is different from rule 5.4!
result = copyNode(arg)
let parameters = arg[0].typ
let L = if parameters != nil: parameters.len else: 0
result.add arg[0]
for i in 1..<arg.len:
result.add pArg(arg[i], c, i < L and parameters[i].kind == tySink)
elif arg.kind in {nkBracket, nkObjConstr, nkTupleConstr, nkBracket, nkCharLit..nkFloat128Lit}:
discard "object construction to sink parameter: nothing to do"
result = arg
elif arg.kind == nkSym and isSinkParam(arg.sym):
# Sinked params can be consumed only once. We need to reset the memory
# to disable the destructor which we have not elided
sinkParamIsLastReadCheck(c, arg)
result = destructiveMoveVar(arg, c)
elif arg.kind == nkSym and arg.sym.kind in InterestingSyms and isLastRead(arg, c):
# it is the last read, can be sinked. We need to reset the memory
# to disable the destructor which we have not elided
result = destructiveMoveVar(arg, c)
elif arg.kind in {nkBlockExpr, nkBlockStmt}:
result = copyNode(arg)
result.add arg[0]
result.add pArg(arg[1], c, isSink)
elif arg.kind == nkStmtListExpr:
result = copyNode(arg)
for i in 0..arg.len-2:
result.add p(arg[i], c)
result.add pArg(arg[^1], c, isSink)
elif arg.kind in {nkIfExpr, nkIfStmt}:
result = copyNode(arg)
for i in 0..<arg.len:
var branch = copyNode(arg[i])
if arg[i].kind in {nkElifBranch, nkElifExpr}:
branch.add p(arg[i][0], c)
branch.add pArgIfTyped(arg[i][1])
else:
branch.add pArgIfTyped(arg[i][0])
result.add branch
elif arg.kind == nkCaseStmt:
result = copyNode(arg)
result.add p(arg[0], c)
for i in 1..<arg.len:
var branch: PNode
if arg[i].kind == nkOfbranch:
branch = arg[i] # of branch conditions are constants
branch[^1] = pArgIfTyped(arg[i][^1])
elif arg[i].kind in {nkElifBranch, nkElifExpr}:
branch = copyNode(arg[i])
branch.add p(arg[i][0], c)
branch.add pArgIfTyped(arg[i][1])
else:
branch = copyNode(arg[i])
branch.add pArgIfTyped(arg[i][0])
result.add branch
else:
# an object that is not temporary but passed to a 'sink' parameter
# results in a copy.
result = passCopyToSink(arg, c)
else:
result = p(arg, c)
proc moveOrCopy(dest, ri: PNode; c: var Con): PNode =
template moveOrCopyIfTyped(ri_part: PNode): PNode =
# typ is nil if we are in if/case expr branch with noreturn
if ri_part.typ == nil: p(ri_part, c)
else: moveOrCopy(dest, ri_part, c)
case ri.kind
of nkCallKinds:
result = genSink(c, dest.typ, dest, ri)
# watch out and no not transform 'ri' twice if it's a call:
let ri2 = copyNode(ri)
let parameters = ri[0].typ
let L = if parameters != nil: parameters.len else: 0
ri2.add ri[0]
for i in 1..<ri.len:
ri2.add pArg(ri[i], c, i < L and parameters[i].kind == tySink)
#recurse(ri, ri2)
result.add ri2
of nkBracketExpr:
if ri[0].kind == nkSym and isUnpackedTuple(ri[0].sym):
# unpacking of tuple: move out the elements
result = genSink(c, dest.typ, dest, ri)
else:
result = genCopy(c, dest.typ, dest, ri)
result.add p(ri, c)
of nkStmtListExpr:
result = newNodeI(nkStmtList, ri.info)
for i in 0..ri.len-2:
result.add p(ri[i], c)
result.add moveOrCopy(dest, ri[^1], c)
of nkBlockExpr, nkBlockStmt:
result = newNodeI(nkBlockStmt, ri.info)
result.add ri[0] ## add label
result.add moveOrCopy(dest, ri[1], c)
of nkIfExpr, nkIfStmt:
result = newNodeI(nkIfStmt, ri.info)
for i in 0..<ri.len:
var branch = copyNode(ri[i])
if ri[i].kind in {nkElifBranch, nkElifExpr}:
branch.add p(ri[i][0], c)
branch.add moveOrCopyIfTyped(ri[i][1])
else:
branch.add moveOrCopyIfTyped(ri[i][0])
result.add branch
of nkCaseStmt:
result = newNodeI(nkCaseStmt, ri.info)
result.add p(ri[0], c)
for i in 1..<ri.len:
var branch: PNode
if ri[i].kind == nkOfbranch:
branch = ri[i] # of branch conditions are constants
branch[^1] = moveOrCopyIfTyped(ri[i][^1])
elif ri[i].kind in {nkElifBranch, nkElifExpr}:
branch = copyNode(ri[i])
branch.add p(ri[i][0], c)
branch.add moveOrCopyIfTyped(ri[i][1])
else:
branch = copyNode(ri[i])
branch.add moveOrCopyIfTyped(ri[i][0])
result.add branch
of nkBracket:
# array constructor
result = genSink(c, dest.typ, dest, ri)
let ri2 = copyTree(ri)
for i in 0..<ri.len:
# everything that is passed to an array constructor is consumed,
# so these all act like 'sink' parameters:
ri2[i] = pArg(ri[i], c, isSink = true)
result.add ri2
of nkObjConstr:
result = genSink(c, dest.typ, dest, ri)
let ri2 = copyTree(ri)
for i in 1..<ri.len:
# everything that is passed to an object constructor is consumed,
# so these all act like 'sink' parameters:
ri2[i].sons[1] = pArg(ri[i][1], c, isSink = true)
result.add ri2
of nkTupleConstr:
result = genSink(c, dest.typ, dest, ri)
let ri2 = copyTree(ri)
for i in 0..<ri.len:
# everything that is passed to an tuple constructor is consumed,
# so these all act like 'sink' parameters:
if ri[i].kind == nkExprColonExpr:
ri2[i].sons[1] = pArg(ri[i][1], c, isSink = true)
else:
ri2[i] = pArg(ri[i], c, isSink = true)
result.add ri2
of nkSym:
if isSinkParam(ri.sym):
# Rule 3: `=sink`(x, z); wasMoved(z)
sinkParamIsLastReadCheck(c, ri)
var snk = genSink(c, dest.typ, dest, ri)
snk.add ri
result = newTree(nkStmtList, snk, genMagicCall(ri, c, "wasMoved", mWasMoved))
elif ri.sym.kind != skParam and isLastRead(ri, c):
# Rule 3: `=sink`(x, z); wasMoved(z)
var snk = genSink(c, dest.typ, dest, ri)
snk.add ri
result = newTree(nkStmtList, snk, genMagicCall(ri, c, "wasMoved", mWasMoved))
else:
result = genCopy(c, dest.typ, dest, ri)
result.add p(ri, c)
else:
result = genCopy(c, dest.typ, dest, ri)
result.add p(ri, c)
proc p(n: PNode; c: var Con): PNode =
case n.kind
of nkVarSection, nkLetSection:
discard "transform; var x = y to var x; x op y where op is a move or copy"
result = newNodeI(nkStmtList, n.info)
for i in 0..<n.len:
let it = n[i]
let L = it.len-1
let ri = it[L]
if it.kind == nkVarTuple and hasDestructor(ri.typ):
let x = lowerTupleUnpacking(c.graph, it, c.owner)
result.add p(x, c)
elif it.kind == nkIdentDefs and hasDestructor(it[0].typ):
for j in 0..L-2:
let v = it[j]
doAssert v.kind == nkSym
# move the variable declaration to the top of the frame:
c.addTopVar v
# make sure it's destroyed at the end of the proc:
if not isUnpackedTuple(it[0].sym):
c.destroys.add genDestroy(c, v.typ, v)
if ri.kind != nkEmpty:
let r = moveOrCopy(v, ri, c)
result.add r
else:
# keep it, but transform 'ri':
var varSection = copyNode(n)
var itCopy = copyNode(it)
for j in 0..L-1:
itCopy.add it[j]
itCopy.add p(ri, c)
varSection.add itCopy
result.add varSection
of nkCallKinds:
let parameters = n[0].typ
let L = if parameters != nil: parameters.len else: 0
for i in 1 ..< n.len:
n.sons[i] = pArg(n[i], c, i < L and parameters[i].kind == tySink)
if n.typ != nil and hasDestructor(n.typ):
discard "produce temp creation"
result = newNodeIT(nkStmtListExpr, n.info, n.typ)
let tmp = getTemp(c, n.typ, n.info)
var sinkExpr = genSink(c, n.typ, tmp, n)
sinkExpr.add n
result.add sinkExpr
result.add tmp
c.destroys.add genDestroy(c, n.typ, tmp)
else:
result = n
of nkAsgn, nkFastAsgn:
if hasDestructor(n[0].typ):
result = moveOrCopy(n[0], n[1], c)
else:
result = copyNode(n)
recurse(n, result)
of nkNone..nkNilLit, nkTypeSection, nkProcDef, nkConverterDef, nkMethodDef,
nkIteratorDef, nkMacroDef, nkTemplateDef, nkLambda, nkDo, nkFuncDef:
result = n
else:
result = copyNode(n)
recurse(n, result)
proc injectDestructorCalls*(g: ModuleGraph; owner: PSym; n: PNode): PNode =
when false: # defined(nimDebugDestroys):
echo "injecting into ", n
var c: Con
c.owner = owner
c.destroys = newNodeI(nkStmtList, n.info)
c.topLevelVars = newNodeI(nkVarSection, n.info)
c.graph = g
c.emptyNode = newNodeI(nkEmpty, n.info)
let cfg = constructCfg(owner, n)
shallowCopy(c.g, cfg)
c.jumpTargets = initIntSet()
for i in 0..<c.g.len:
if c.g[i].kind in {goto, fork}:
c.jumpTargets.incl(i+c.g[i].dest)
#if owner.name.s == "test0p1":
# echoCfg(c.g)
if owner.kind in {skProc, skFunc, skMethod, skIterator, skConverter}:
let params = owner.typ.n
for i in 1 ..< params.len:
let param = params[i].sym
if param.typ.kind == tySink and hasDestructor(param.typ):
c.destroys.add genDestroy(c, param.typ.skipTypes({tyGenericInst, tyAlias, tySink}), params[i])
let body = p(n, c)
result = newNodeI(nkStmtList, n.info)
if c.topLevelVars.len > 0:
result.add c.topLevelVars
if c.destroys.len > 0:
result.add newTryFinally(body, c.destroys)
else:
result.add body
when defined(nimDebugDestroys):
if true:
echo "------------------------------------"
echo owner.name.s, " transformed to: "
echo result