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Diffstat (limited to 'compiler/semparallel.nim')
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diff --git a/compiler/semparallel.nim b/compiler/semparallel.nim new file mode 100644 index 000000000..c594a4788 --- /dev/null +++ b/compiler/semparallel.nim @@ -0,0 +1,465 @@ +# +# +# The Nimrod Compiler +# (c) Copyright 2014 Andreas Rumpf +# +# See the file "copying.txt", included in this +# distribution, for details about the copyright. +# + +## Semantic checking for 'parallel'. + +# - codegen needs to support mSlice (+) +# - lowerings must not perform unnecessary copies (+) +# - slices should become "nocopy" to openArray (+) +# - need to perform bound checks (+) +# +# - parallel needs to insert a barrier (+) +# - passed arguments need to be ensured to be "const" +# - what about 'f(a)'? --> f shouldn't have side effects anyway +# - passed arrays need to be ensured not to alias +# - passed slices need to be ensured to be disjoint (+) +# - output slices need special logic (+) + +import + ast, astalgo, idents, lowerings, magicsys, guards, sempass2, msgs, + renderer +from trees import getMagic +from strutils import `%` + +discard """ + +one major problem: + spawn f(a[i]) + inc i + spawn f(a[i]) +is valid, but + spawn f(a[i]) + spawn f(a[i]) + inc i +is not! However, + spawn f(a[i]) + if guard: inc i + spawn f(a[i]) +is not valid either! --> We need a flow dependent analysis here. + +However: + while foo: + spawn f(a[i]) + inc i + spawn f(a[i]) + +Is not valid either! --> We should really restrict 'inc' to loop endings? + +The heuristic that we implement here (that has no false positives) is: Usage +of 'i' in a slice *after* we determined the stride is invalid! +""" + +type + TDirection = enum + ascending, descending + MonotonicVar = object + v, alias: PSym # to support the ordinary 'countup' iterator + # we need to detect aliases + lower, upper, stride: PNode + dir: TDirection + blacklisted: bool # blacklisted variables that are not monotonic + AnalysisCtx = object + locals: seq[MonotonicVar] + slices: seq[tuple[x,a,b: PNode, spawnId: int, inLoop: bool]] + guards: TModel # nested guards + args: seq[PSym] # args must be deeply immutable + spawns: int # we can check that at last 1 spawn is used in + # the 'parallel' section + currentSpawnId: int + inLoop: int + +let opSlice = createMagic("slice", mSlice) + +proc initAnalysisCtx(): AnalysisCtx = + result.locals = @[] + result.slices = @[] + result.args = @[] + result.guards = @[] + +proc lookupSlot(c: AnalysisCtx; s: PSym): int = + for i in 0.. <c.locals.len: + if c.locals[i].v == s or c.locals[i].alias == s: return i + return -1 + +proc getSlot(c: var AnalysisCtx; v: PSym): ptr MonotonicVar = + let s = lookupSlot(c, v) + if s >= 0: return addr(c.locals[s]) + let L = c.locals.len + c.locals.setLen(L+1) + c.locals[L].v = v + return addr(c.locals[L]) + +proc gatherArgs(c: var AnalysisCtx; n: PNode) = + for i in 0.. <n.safeLen: + let root = getRoot n[i] + if root != nil: + block addRoot: + for r in items(c.args): + if r == root: break addRoot + c.args.add root + gatherArgs(c, n[i]) + +proc isSingleAssignable(n: PNode): bool = + n.kind == nkSym and (let s = n.sym; + s.kind in {skTemp, skForVar, skLet} and + {sfAddrTaken, sfGlobal} * s.flags == {}) + +proc isLocal(n: PNode): bool = + n.kind == nkSym and (let s = n.sym; + s.kind in {skResult, skTemp, skForVar, skVar, skLet} and + {sfAddrTaken, sfGlobal} * s.flags == {}) + +proc checkLocal(c: AnalysisCtx; n: PNode) = + if isLocal(n): + let s = c.lookupSlot(n.sym) + if s >= 0 and c.locals[s].stride != nil: + localError(n.info, "invalid usage of counter after increment") + else: + for i in 0 .. <n.safeLen: checkLocal(c, n.sons[i]) + +template `?`(x): expr = x.renderTree + +proc checkLe(c: AnalysisCtx; a, b: PNode) = + case proveLe(c.guards, a, b) + of impUnknown: + localError(a.info, "cannot prove: " & ?a & " <= " & ?b) + of impYes: discard + of impNo: + localError(a.info, "can prove: " & ?a & " > " & ?b) + +proc checkBounds(c: AnalysisCtx; arr, idx: PNode) = + checkLe(c, arr.lowBound, idx) + checkLe(c, idx, arr.highBound) + +proc addLowerBoundAsFacts(c: var AnalysisCtx) = + for v in c.locals: + if not v.blacklisted: + c.guards.addFactLe(v.lower, newSymNode(v.v)) + +proc addSlice(c: var AnalysisCtx; n: PNode; x, le, ri: PNode) = + checkLocal(c, n) + let le = le.canon + let ri = ri.canon + # perform static bounds checking here; and not later! + let oldState = c.guards.len + addLowerBoundAsFacts(c) + c.checkBounds(x, le) + c.checkBounds(x, ri) + c.guards.setLen(oldState) + c.slices.add((x, le, ri, c.currentSpawnId, c.inLoop > 0)) + +proc overlap(m: TModel; x,y,c,d: PNode) = + # X..Y and C..D overlap iff (X <= D and C <= Y) + case proveLe(m, x, d) + of impUnknown: + localError(x.info, + "cannot prove: $# > $#; required for ($#)..($#) disjoint from ($#)..($#)" % + [?x, ?d, ?x, ?y, ?c, ?d]) + of impYes: + case proveLe(m, c, y) + of impUnknown: + localError(x.info, + "cannot prove: $# > $#; required for ($#)..($#) disjoint from ($#)..($#)" % + [?c, ?y, ?x, ?y, ?c, ?d]) + of impYes: + localError(x.info, "($#)..($#) not disjoint from ($#)..($#)" % [?x, ?y, ?c, ?d]) + of impNo: discard + of impNo: discard + +proc stride(c: AnalysisCtx; n: PNode): BiggestInt = + if isLocal(n): + let s = c.lookupSlot(n.sym) + if s >= 0 and c.locals[s].stride != nil: + result = c.locals[s].stride.intVal + else: + for i in 0 .. <n.safeLen: result += stride(c, n.sons[i]) + +proc subStride(c: AnalysisCtx; n: PNode): PNode = + # substitute with stride: + if isLocal(n): + let s = c.lookupSlot(n.sym) + if s >= 0 and c.locals[s].stride != nil: + result = n +@ c.locals[s].stride.intVal + else: + result = n + elif n.safeLen > 0: + result = shallowCopy(n) + for i in 0 .. <n.len: result.sons[i] = subStride(c, n.sons[i]) + else: + result = n + +proc checkSlicesAreDisjoint(c: var AnalysisCtx) = + # this is the only thing that we need to perform after we have traversed + # the whole tree so that the strides are available. + # First we need to add all the computed lower bounds: + addLowerBoundAsFacts(c) + # Every slice used in a loop needs to be disjoint with itself: + for x,a,b,id,inLoop in items(c.slices): + if inLoop: overlap(c.guards, a,b, c.subStride(a), c.subStride(b)) + # Another tricky example is: + # while true: + # spawn f(a[i]) + # spawn f(a[i+1]) + # inc i # inc i, 2 would be correct here + # + # Or even worse: + # while true: + # spawn f(a[i+1 .. i+3]) + # spawn f(a[i+4 .. i+5]) + # inc i, 4 + # Prove that i*k*stride + 3 != i*k'*stride + 5 + # For the correct example this amounts to + # i*k*2 != i*k'*2 + 1 + # which is true. + # For now, we don't try to prove things like that at all, even though it'd + # be feasible for many useful examples. Instead we attach the slice to + # a spawn and if the attached spawns differ, we bail out: + for i in 0 .. high(c.slices): + for j in i+1 .. high(c.slices): + let x = c.slices[i] + let y = c.slices[j] + if x.spawnId != y.spawnId and guards.sameTree(x.x, y.x): + if not x.inLoop or not y.inLoop: + # XXX strictly speaking, 'or' is not correct here and it needs to + # be 'and'. However this prevents too many obviously correct programs + # like f(a[0..x]); for i in x+1 .. a.high: f(a[i]) + overlap(c.guards, x.a, x.b, y.a, y.b) + elif (let k = simpleSlice(x.a, x.b); let m = simpleSlice(y.a, y.b); + k >= 0 and m >= 0): + # ah I cannot resist the temptation and add another sweet heuristic: + # if both slices have the form (i+k)..(i+k) and (i+m)..(i+m) we + # check they are disjoint and k < stride and m < stride: + overlap(c.guards, x.a, x.b, y.a, y.b) + let stride = min(c.stride(x.a), c.stride(y.a)) + if k < stride and m < stride: + discard + else: + localError(x.x.info, "cannot prove ($#)..($#) disjoint from ($#)..($#)" % + [?x.a, ?x.b, ?y.a, ?y.b]) + else: + localError(x.x.info, "cannot prove ($#)..($#) disjoint from ($#)..($#)" % + [?x.a, ?x.b, ?y.a, ?y.b]) + +proc analyse(c: var AnalysisCtx; n: PNode) + +proc analyseSons(c: var AnalysisCtx; n: PNode) = + for i in 0 .. <safeLen(n): analyse(c, n[i]) + +proc min(a, b: PNode): PNode = + if a.isNil: result = b + elif a.intVal < b.intVal: result = a + else: result = b + +proc fromSystem(op: PSym): bool = sfSystemModule in getModule(op).flags + +proc analyseCall(c: var AnalysisCtx; n: PNode; op: PSym) = + if op.magic == mSpawn: + inc c.spawns + let oldSpawnId = c.currentSpawnId + c.currentSpawnId = c.spawns + gatherArgs(c, n[1]) + analyseSons(c, n) + c.currentSpawnId = oldSpawnId + elif op.magic == mInc or (op.name.s == "+=" and op.fromSystem): + if n[1].isLocal: + let incr = n[2].skipConv + if incr.kind in {nkCharLit..nkUInt32Lit} and incr.intVal > 0: + let slot = c.getSlot(n[1].sym) + slot.stride = min(slot.stride, incr) + analyseSons(c, n) + elif op.name.s == "[]" and op.fromSystem: + c.addSlice(n, n[1], n[2][1], n[2][2]) + analyseSons(c, n) + elif op.name.s == "[]=" and op.fromSystem: + c.addSlice(n, n[1], n[2][1], n[2][2]) + analyseSons(c, n) + else: + analyseSons(c, n) + +proc analyseCase(c: var AnalysisCtx; n: PNode) = + analyse(c, n.sons[0]) + let oldFacts = c.guards.len + for i in 1.. <n.len: + let branch = n.sons[i] + setLen(c.guards, oldFacts) + addCaseBranchFacts(c.guards, n, i) + for i in 0 .. <branch.len: + analyse(c, branch.sons[i]) + setLen(c.guards, oldFacts) + +proc analyseIf(c: var AnalysisCtx; n: PNode) = + analyse(c, n.sons[0].sons[0]) + let oldFacts = c.guards.len + addFact(c.guards, canon(n.sons[0].sons[0])) + + analyse(c, n.sons[0].sons[1]) + for i in 1.. <n.len: + let branch = n.sons[i] + setLen(c.guards, oldFacts) + for j in 0..i-1: + addFactNeg(c.guards, canon(n.sons[j].sons[0])) + if branch.len > 1: + addFact(c.guards, canon(branch.sons[0])) + for i in 0 .. <branch.len: + analyse(c, branch.sons[i]) + setLen(c.guards, oldFacts) + +proc analyse(c: var AnalysisCtx; n: PNode) = + case n.kind + of nkAsgn, nkFastAsgn: + if n[0].isSingleAssignable and n[1].isLocal: + let slot = c.getSlot(n[1].sym) + slot.alias = n[0].sym + elif n[0].isLocal: + # since we already ensure sfAddrTaken is not in s.flags, we only need to + # prevent direct assignments to the monotonic variable: + let slot = c.getSlot(n[0].sym) + slot.blackListed = true + invalidateFacts(c.guards, n[0]) + analyseSons(c, n) + addAsgnFact(c.guards, n[0], n[1]) + of nkCallKinds: + # direct call: + if n[0].kind == nkSym: analyseCall(c, n, n[0].sym) + else: analyseSons(c, n) + of nkBracketExpr: + c.addSlice(n, n[0], n[1], n[1]) + analyseSons(c, n) + of nkReturnStmt, nkRaiseStmt, nkTryStmt: + localError(n.info, "invalid control flow for 'parallel'") + # 'break' that leaves the 'parallel' section is not valid either + # or maybe we should generate a 'try' XXX + of nkVarSection: + for it in n: + let value = it.lastSon + if value.kind != nkEmpty: + for j in 0 .. it.len-3: + if it[j].isLocal: + let slot = c.getSlot(it[j].sym) + if slot.lower.isNil: slot.lower = value + else: internalError(it.info, "slot already has a lower bound") + analyse(c, value) + of nkCaseStmt: analyseCase(c, n) + of nkIfStmt, nkIfExpr: analyseIf(c, n) + of nkWhileStmt: + analyse(c, n.sons[0]) + # 'while true' loop? + inc c.inLoop + if isTrue(n.sons[0]): + analyseSons(c, n.sons[1]) + else: + # loop may never execute: + let oldState = c.locals.len + let oldFacts = c.guards.len + addFact(c.guards, canon(n.sons[0])) + analyse(c, n.sons[1]) + setLen(c.locals, oldState) + setLen(c.guards, oldFacts) + # we know after the loop the negation holds: + if not hasSubnodeWith(n.sons[1], nkBreakStmt): + addFactNeg(c.guards, canon(n.sons[0])) + dec c.inLoop + of nkTypeSection, nkProcDef, nkConverterDef, nkMethodDef, nkIteratorDef, + nkMacroDef, nkTemplateDef, nkConstSection, nkPragma: + discard + else: + analyseSons(c, n) + +proc transformSlices(n: PNode): PNode = + if n.kind in nkCallKinds and n[0].kind == nkSym: + let op = n[0].sym + if op.name.s == "[]" and op.fromSystem: + result = copyNode(n) + result.add opSlice.newSymNode + result.add n[1] + result.add n[2][1] + result.add n[2][2] + return result + if n.safeLen > 0: + result = shallowCopy(n) + for i in 0 .. < n.len: + result.sons[i] = transformSlices(n.sons[i]) + else: + result = n + +proc transformSpawn(owner: PSym; n, barrier: PNode): PNode +proc transformSpawnSons(owner: PSym; n, barrier: PNode): PNode = + result = shallowCopy(n) + for i in 0 .. < n.len: + result.sons[i] = transformSpawn(owner, n.sons[i], barrier) + +proc transformSpawn(owner: PSym; n, barrier: PNode): PNode = + case n.kind + of nkVarSection: + result = nil + for it in n: + let b = it.lastSon + if getMagic(b) == mSpawn: + if it.len != 3: localError(it.info, "invalid context for 'spawn'") + let m = transformSlices(b) + if result.isNil: + result = newNodeI(nkStmtList, n.info) + result.add n + result.add wrapProcForSpawn(owner, m, b.typ, barrier, it[0]) + it.sons[it.len-1] = emptyNode + if result.isNil: result = n + of nkAsgn, nkFastAsgn: + let b = n[1] + if getMagic(b) == mSpawn: + let m = transformSlices(b) + return wrapProcForSpawn(owner, m, b.typ, barrier, n[0]) + result = transformSpawnSons(owner, n, barrier) + of nkCallKinds: + if getMagic(n) == mSpawn: + result = transformSlices(n) + return wrapProcForSpawn(owner, result, n.typ, barrier, nil) + result = transformSpawnSons(owner, n, barrier) + elif n.safeLen > 0: + result = transformSpawnSons(owner, n, barrier) + else: + result = n + +proc checkArgs(a: var AnalysisCtx; n: PNode) = + discard "too implement" + +proc generateAliasChecks(a: AnalysisCtx; result: PNode) = + discard "too implement" + +proc liftParallel*(owner: PSym; n: PNode): PNode = + # this needs to be called after the 'for' loop elimination + + # first pass: + # - detect monotonic local integer variables + # - detect used slices + # - detect used arguments + #echo "PAR ", renderTree(n) + + var a = initAnalysisCtx() + let body = n.lastSon + analyse(a, body) + if a.spawns == 0: + localError(n.info, "'parallel' section without 'spawn'") + checkSlicesAreDisjoint(a) + checkArgs(a, body) + + var varSection = newNodeI(nkVarSection, n.info) + var temp = newSym(skTemp, getIdent"barrier", owner, n.info) + temp.typ = magicsys.getCompilerProc("Barrier").typ + incl(temp.flags, sfFromGeneric) + let tempNode = newSymNode(temp) + varSection.addVar tempNode + + let barrier = genAddrOf(tempNode) + result = newNodeI(nkStmtList, n.info) + generateAliasChecks(a, result) + result.add varSection + result.add callCodeGenProc("openBarrier", barrier) + result.add transformSpawn(owner, body, barrier) + result.add callCodeGenProc("closeBarrier", barrier) + |